Raw pasta is a convenient environment for various biochemical and microbiological processes. To prevent the development of these processes, the products are subjected to conservation by drying to a moisture content of not more than 13%.
Drying pasta is the longest stage in the process of their production. From the modes of its implementation, such indicators of the quality of the finished product as strength, vitreousness in fracture, and acidity largely depend. Intensive drying can lead to cracking of products; excessively prolonged drying at the first stage of moisture removal - to souring, swelling of products; when drying in a layer - to the formation of ingots, deformation of products.
Drying is completed when the products reach a moisture content of 13.5-14%, so that after cooling, before packaging, their moisture content is no more than 13%.
convective drying method
The convective drying method is based on heat and moisture exchange between the dried material and heated drying air, which blows over the products. The drying process consists in the supply of moisture inside the product to its surface, the transformation of moisture into steam and the removal of steam from the surface of the product. In this case, the drying air performs the following main functions:
a) gives the material the energy (heat) necessary to turn water into steam;
b) absorbs steam evaporating from the surface of products;
c) removes evaporated steam from the product.
The main parameters of drying air that determine the rate of drying of products are temperature, relative humidity and speed. The higher the temperature of the drying air, the more intense the evaporation of moisture from the surface of the products; the lower the relative humidity of the air, i.e. the “drier” it is, the more intensively it will absorb evaporating moisture, and the higher the speed of air movement over the products, the faster the evaporated moisture will be removed from them.
The movement of moisture from the inner layers of the material to the outer ones occurs under the influence of a moisture gradient, i.e. differences in the moisture content of the layers resulting from the evaporation of moisture from the surface of the material and the drying of the outer layers. The moisture gradient is directed towards the center of the products to be dried, i.e. in the direction opposite to the movement of moisture. Its value is the greater, the more intensively the drying of the outer layers occurs. The phenomenon of moisture movement under the influence of a moisture gradient is called moisture conductivity, or concentration diffusion.
When drying pasta with air with certain parameters, the moisture content of the dried products will gradually decrease to a certain value, called the equilibrium moisture content. Drying air with certain parameters (temperature, humidity) corresponds to a certain equilibrium humidity of products, which will not decrease, no matter how much the products are blown with this air.
For the correct choice of drying mode, it is very important to know the values of the equilibrium moisture content of pasta, which are determined from the equilibrium moisture curves.
Changing the properties of pasta during drying
A feature of drying pasta is the change in their structural and mechanical properties and dimensions. During drying, the moisture content of the product decreases from 29-30% to 13-14%, while there is a gradual reduction in linear and volumetric dimensions, shrinkage of products is 6-8%.
Raw products supplied for drying are a plastic material and retain their plastic properties up to about 20% humidity. With a decrease in humidity from about 20 to 16%, they gradually lose the properties of a plastic material and acquire the properties characteristic of an elastic material. With such humidity, pasta is an elastic-plastic body.
Starting from about 16% moisture, pasta becomes a solid elastic body and retains its properties until the end of drying.
With soft drying modes, i.e. slow drying with air with low drying capacity, the difference in humidity between the outer and inner layers is small, since moisture from the wetter inner layers has time to move to the dried outer layers. All layers of products are reduced approximately evenly. The drying capacity of air is characterized by the amount of moisture that can absorb 1 kg of air until it is completely saturated, i.e. up to 100% humidity.
With hard drying conditions, i.e. intensive drying with air with high drying capacity, the difference in humidity between the outer and central layers reaches a significant value due to the fact that moisture from the inner layers does not have time to move to the outer ones. The drier outer layers tend to shorten their length, which is hindered by the wetter inner layers. At the boundary of the layers, stresses arise, called internal shear stresses, the magnitude of which is the greater, the more intensively moisture is removed from the surface of the products and the greater the difference in humidity (humidity gradient).
As long as the dried pasta retains plastic properties, the resulting internal shear stresses are absorbed, i.e. products change their shape under the influence of stresses without collapsing. When the product acquires the properties of an elastic body, the resulting internal shear stresses, if they exceed the maximum allowable, critical values, lead to the destruction of products - the appearance of microcracks, which, ultimately, can turn products into crumbs.
Thus, pasta can be dried under strict conditions, without fear of cracking, up to a moisture content of 20%. When the product reaches this moisture content, in order to avoid cracking, it is necessary to carry out drying under mild conditions, slowly removing moisture. Particular care should be taken to remove moisture in the last stages of drying when the products reach a moisture content of 16% or less. This conclusion finds practical application when drying products in dryers of modern production lines, in which the drying process is divided into two stages - preliminary and final drying.
Drying modes for products
The term drying mode is understood as a set of parameters of the drying air (temperature, relative humidity, air velocity) and the duration of drying. The optimal drying mode for a certain type of pasta is considered to be such a mode in which products of normal quality are obtained with the shortest drying time and energy consumption.
Currently, the modes of convective drying of pasta are used:
traditional low-temperature ones with drying air temperature up to 60 С;
high-temperature with the temperature of the drying air from 70 to 90 С;
ultra-high temperature with a temperature of more than 90 С.
For drying pasta, the most common low-temperature modes are: with constant drying capacity, with varying drying capacity, three-stage.
Drying with constant air drying capacity. Drying of products is carried out in cupboard non-calorific dryers such as GDP, "Diffuser" and 2TsAGI-700.
Cassettes filled with raw pasta are placed either on trolleys, which are taken to the drying department, where the cassettes are placed on the shelves of the dryers, or in trolley cabinets, which are placed close to the drying cabinets.
Cassettes on the shelves of dryers or in trolleys are stacked in several rows in width and height.
Cabinet dryers are equipped with ventilation units. Drying of pasta is carried out by blowing air through pasta tubes lying in cassettes. The air from the workshop is used to dry the pasta. For uniform drying, periodically (after 1 hour) change the direction of air movement to the opposite, switching the electric motor to work in the opposite direction.
In the drying shop, air parameters are maintained at a constant level with the help of supply and exhaust ventilation, i.e. air has a constant drying capacity, namely: a temperature of about 30 ° C and a relative humidity of 65-70%. The air in the workshop is heated either by a battery of heating radiators or a heater, through which fresh air is injected into the workshop instead of the humidified exhaust air sucked from the workshop. Drying time is about 24 hours.
When drying in tray cassettes, pasta is blown with air from the inner and outer surfaces of the tubes. Due to uneven contact of pasta with each other, uneven removal of moisture from their surface occurs, and, consequently, uneven shrinkage of products. This leads to the curvature of products during drying, which significantly reduces their quality, increases the consumption of containers for packaging. The contact of the tubes in the cassette and the inability to quickly remove moisture in the initial stage of drying lead to sticking of products, the formation of ingots.
The disadvantage of this method of drying are also the high costs of manual labor and the discomfort of the room (high temperature and humidity) in which the drying is carried out.
Three-stage drying mode. The mode consists of three stages (preliminary drying, softening, final drying). Drying of long products in the hanging way. Drying of long pasta (vermicelli and noodles of various types, pasta straws and special ones) is carried out in tunnel dryers (preliminary and final) of automated production lines B6-LMG, B6-LMV, LMB and in the lines of the Braibanti company. Products hung on bastuns slowly move in the tunnels of the dryers, blowing air from top to bottom.
The purpose of pre-drying is to quickly remove moisture from raw pasta at that stage, while they have plastic properties. The main purpose of this stage is to reduce the overall drying time of the pasta. A rapid decrease in the humidity of products prevents the development of various microbiological and biochemical processes, primarily souring, swelling and darkening of pasta.
The parameters of the drying air in the preliminary dryer, depending on the products, are: temperature 35-45 °C, relative humidity 65-75%. The moisture content of the semi-finished product at the stage of pre-drying is reduced to 20%. The duration of pre-drying on these lines is about 3 hours.
The final dryers are divided along the length into drying and curing zones.
In the tempering zones (second stage), the relative humidity of the air is close to saturation (to 100%), so there is no evaporation of moisture from the surface of the products. In these zones, the temperature and humidity of the product are equalized in all internal layers: the slow migration of moisture inside the products to the surface, from where the moisture was removed while the products were in the previous drying zone. In this case, the internal shear stresses resulting from this removal are absorbed.
In the drying zones (third stage), fans and heaters are installed, with the help of which the drying air heats up and blows over the products hanging on the bastuns. The air temperature in the final drying zones, as in the pre-dryer, is 35-45 °C, and the relative air humidity is slightly higher - 70-85%.
Bastuns with products alternately cross the drying zone and the softening zone. Thus, the removal of moisture from the product is carried out in steps, i.e. periods of drying alternate with periods of softening. As a result of the so-called pulsating drying regime, durable products with a vitreous fracture are obtained.
The duration of the final drying of products depends on the assortment and averages from 11 to 15 hours. Products leaving the final dryer chamber with a moisture content of 13.5-14% are sent to the stabilization chamber for cooling.
Drying of short products in dryers of automatic production lines. Drying of short (short-cut and stamped) products in dryers (preliminary and final) of automatic production lines is carried out in three stages. The pre-drying and final drying stages are preceded by a primary drying stage. It is carried out in installations (trabatto), where raw products make "jumping" movements, blown for 2-3 minutes. hot air. A dried layer is formed on the surface of the products, which prevents them from sticking together during the subsequent drying "in a layer" on the belts of conveyor dryers.
Drying with changing air capacity. Drying of short products in steam conveyor dryers. Raw products are distributed by the spreader onto the belt of the upper conveyor of the dryer, slowly move in the opposite direction, poured onto the belt of the next conveyor, and so on - up to the lower conveyor, which is fed for unloading.
The layers of products lying on the conveyor belts are permeated with drying air, which is sucked in at the bottom and thrown out at the top of the dryer. Fresh air is heated by the lower air heater to a temperature of 50-60 °C and a relative humidity of 15-20%. Then the heated drying air passes through the layer of products lying on the lower conveyor, gives them part of the heat and is moistened. After passing through the second heater, the air heats up again to approximately the same temperature, passes a layer of products lying on the belt of the second conveyor, and so on - up to the upper conveyor. The parameters of the used drying air at the outlet of the dryer are approximately the following: temperature 40-50 °C, relative humidity 50-60%. Such a drying mode is called a mode with an increasing drying capacity of air: as the product dries, it is blown with drier air.
The duration of drying products (up to a moisture content of 13.5-14%) is, depending on the assortment, from 30 (for vermicelli and soup fillings) to 90 minutes (for large figured products).
The use of such harsh drying conditions often leads to the formation of cracks on the surface of dried products, especially tubular (feathers, horns) and curly (shells, etc.). The advantages of this mode are the high productivity of these dryers with small overall dimensions, as well as the relative simplicity of their maintenance and reliability.
High temperature drying. This mode, in comparison with the traditional mode, allows to reduce energy costs and reduce production areas per unit of output, reduce the drying time by an average of 40-50% and, with properly selected drying modes, improve the quality of pasta (color and cooking properties) and their microbiological state.
High-temperature drying can be carried out in conventional dryers of production lines, while either increasing the productivity of the line by including more powerful presses and increasing the speed of the conveyors of the dryers, or reducing the length of the dryers of the line while maintaining its productivity.
When developing modes of high-temperature drying of pasta, it is necessary to proceed from the following basic prerequisites:
the drying process should be carried out in two main stages: preliminary and final drying;
the temperature of the drying air should be (at one of the stages) in the range of 60-90 °C. The use of such an interval is due to the fact that 60 ° C is the minimum limit for the complete pasteurization of pasta, and 90 ° C is the temperature at which the Maillard melanoidin reaction is likely to occur (non-enzymatic darkening of the product);
drying of products should be carried out at high relative humidity in order to avoid excessive removal of moisture from the surface layers of products and the occurrence of dangerous shear stresses between the inner layers of products, which can lead to cracking of the product, turning it into scrap.
Ultra-high temperature drying. At present, all the leading companies in the industry - Pavan, Buhler, Bassano - produce lines for the production of short pasta with ultra-high-temperature drying mode. These modes are characterized by the use of drying air with a temperature of more than 90 С and a relative humidity of about 90%, drying in 3 stages. The advantages of ultrahigh-temperature drying modes are: reduction of the drying process due to the acceleration of mass transfer; improvement of the microbiological state of products and sanitary and hygienic conditions of production; improving the quality, cooking properties of products, which is especially important when processing soft wheat flour; reduction of energy consumption by 10-15% and reduction of production space per unit of output.
Drying with preliminary heat treatment of raw products. Heat treatment of products before drying can significantly reduce the process of their dehydration, since it will allow you to apply harsh drying conditions without fear of cracking. This is due to thermal denaturation of proteins and partial gelatinization of starch, which leads to a decrease in the binding energy of these components with moisture.
Nazarov proposed a method for processing raw long pasta with a steam-air mixture at a temperature of 95-98 ° C and a relative humidity of 95% for 2 minutes, and short-cut products - with dry steam at a temperature of 120-180 ° C for 30 s, followed by drying the product under severe conditions.
Product cooling
Pasta products leaving the dryer usually have an elevated temperature equal to the temperature of the drying air. Before packaging, it must be cooled to the temperature of the packaging compartment. With slow cooling, the products stabilize: the moisture is finally leveled over the entire thickness of the products, the internal shear stresses remaining after drying are absorbed, as well as a slight decrease in the mass of the cooling products due to the evaporation of 0.5-1% of moisture from them.
The minimum duration of stabilization is 4 hours, while the products are washed with air at a temperature of 25-30 ° C and a relative humidity of 60-65%.
Rapid cooling of dried products by intensive blowing in coolers of various designs or their cooling on belt conveyors when fed to packaging is undesirable. Dried products in a short time (about 5 minutes) have time to cool down to the temperature of the shop and their subsequent shrinkage after packaging does not occur, however, in a short period of time, internal shear stresses not only do not have time to disappear, but also increase, and if the products were subjected to excessively intensive drying , cracking them and turning into crumbs can occur after packaging. In modern automated production lines, the stabilization chambers simultaneously act as accumulators: they accumulate products produced during the night shift, which makes it possible to organize the packaging of products only during the day and evening shifts.
Basic Methods for Drying Pasta
Ways to intensify the drying of pasta
Biochemical changes in starch and protein of pasta and their technological characteristics during heat treatment and drying
Changes in the structural and mechanical properties of pasta subjected to hygrothermal treatment
Mass transfer characteristics and equilibrium critical moisture content of pasta
Installation for drying pasta using a new technology and justification for the feasibility of introducing a new drying method
INTRODUCTION
Due to the low humidity, pasta can be stored for a long time. Drying them is an energy-intensive and time-consuming process of all technological stages of pasta production. Recently, much attention has been paid to the preliminary preparation of the drying object for dehydration. The purpose of such preparation is to reduce the binding energy of moisture with the material and change its thermophysical characteristics, which make it possible to use "hard" drying modes without compromising the quality of the dried product.
BASIC METHODS FOR DRYING PASTA
In the pasta industry, convective drying is mainly used. Varieties of drying plants have been developed - from closed chambers to modern drying, tunnel, continuously operating units equipped with automatic control systems for drying mode parameters. However, even with a high degree of mechanization and automation of these installations, the drying process of products remains lengthy. There are many studies devoted to the problem of intensifying this process by increasing the drying capacity of air; application of new drying methods; thermoradiation, radiation-convective, sublimation, etc.
The drying modes used in the pasta industry are varied. When choosing the optimal drying mode, it is necessary to take into account the technological properties of pasta dough.
It is known that two types of modes are mainly used for convective drying: continuous and pulsating.
Continuous drying at a constant drying capacity of the air is simple in terms of air and process control. The air parameters in this drying mode remain constant throughout the entire dehydration process.
The main disadvantage of the continuous mode is that the drying is carried out with a high drying capacity of the air. This mode can only be used for products resistant to deformation: soup fillings and powdered products. Their drying takes place in a shorter time than long-tube ones, their dimensions are smaller, they are better amenable to comprehensive air blowing due to pouring.
Long-tubular products are dried in a three-stage or pulsating mode. The latter is conditionally divided into the following stages. The first stage is pre-drying. Its purpose is to stabilize the shape of products to prevent hanging, molding and stretching. "Drying"" lasts from 30 minutes to 2 hours and proceeds under relatively "hard" modes, during which from 1/3 to half of the moisture is removed from the amount that should be removed during drying from pasta.
Such intensive dehydration is possible only at the first stage of drying, when the pasta dough is plastic and there is no danger of cracking. Further conduct of the process in the "hard" mode is impossible, since this will lead to cracking of the products, the resulting large moisture gradient and increased stresses cannot be reduced, since the pasta dough has acquired the properties of an elastic body.
To avoid cracking, the second stage is carried out - softening. By increasing the relative humidity of the air, a "softening of the crust" is achieved by moistening the surface layer; as a result, the humidity gradient decreases and the resulting stresses are absorbed. This process is best carried out at relatively high temperatures and relative air humidity, at which the rate of moisture diffusion increases, and the evaporation of moisture from the surface decreases. Under these conditions, the tempering time is reduced.
The third stage - the final drying - is carried out in a "soft" mode so that the tangential stresses do not exceed the limit value, since the products are in a state of elastic deformation. In this case, the rate of moisture evaporation from the surface should be commensurate with the rate of its supply from the inner layers to the upper layer. At this stage, drying can be alternated with softening.
It is important that the products are cooled slowly after drying, so that the moisture gradient is minimal at the time of packaging. With sudden cooling, cracks may form due to insufficient leveling of moisture content over the layers of the product.
THEM. Savina investigated the three-stage mode of drying short-cut products. It has been established that the total duration of drying is greatly influenced by the amount of moisture removed during the pre-drying period. A three-stage drying mode was compared with continuous drying at constant air parameters (t = 60 °C; φ = 70%; V = 0.9 m/s). In both cases, a good quality of the product was obtained, however, the duration of drying in a three-stage mode was 20-25% shorter.
IT Taranym proposed a 5-stage mode for drying long-tube pasta: pre-drying; short-term (deep) softening; re-drying; long-term (surface) softening and drying.
The use of a multi-stage mode significantly reduced the duration of the drying process to 10-12 hours.
In the pasta laboratory of VNIIKhP, work was carried out to study the drying of pasta in rotating cylindrical cassettes according to the method of the French company Bassane .
The possibility of obtaining straight tubular pasta has been proved and it has been established that a cylindrical cassette should have a ratio D/L = 0.47, end walls - solid, smooth, without perforations. Items with a moisture content of no more than 29% should be placed in the cassette. ; fill the volume of the cassette with raw products by 62-65%. The dependence of the speed of blowing pasta with air flow on the free section of the cassette at different frequencies of its swing has been found.
On the basis of experimental data, the most optimal value of the area of the open section of the shell for the cassette was revealed - 45%.
It is recommended that pre-drying be carried out with a drying agent (air temperature 50 °C and relative humidity 65%) at a speed of 5 m/s s with a cassette swing amplitude of 140 °C and a swing frequency of 15-12 swings per minute. The drying time is 1.5 hours, the final moisture content of the semi-finished product is 22%.
After pre-drying, before the start of final drying, the product must be hardened for 60 minutes at an air temperature of 47 ° C, a humidity of 88-94% and a cassette rotation frequency of 2 rpm.
Final drying must be carried out with air at the following parameters: temperature - 50 °C, relative humidity - 80%, air flow rate - 5 m/sec. Cassette swing amplitude - 180 °C, swing frequency - 15 swings per minute, swing and blowing duration - 20 min; softening should be carried out for 40 minutes at an air temperature of 47 ° C, a relative humidity of 88-94%, a cassette rotation frequency of 2 rpm. Then the cycle repeats. The total duration of drying pasta is 17-18 hours.
Currently, in various industries, the thermoradiation method of energy supply is used, in which the intensification of the drying process is achieved through the use of short-wave infrared radiation.
The issue of using infrared radiation for drying pasta was first studied by A. S. Ginzburg, I. Kh. Melnikova, N. A. Lukyanova, I. M. Savina and others.
It is noted that due to the peculiarities of moisture movement under the action of infrared rays, a very rapid dehydration of the surface layer is observed due to the appearance of a significant temperature difference inside the material. As a result of a sharp decrease in surface moisture, uneven shrinkage of adjacent layers occurs, which causes cracking of the material. As a result, continuous irradiation cannot be used when drying pasta and pasta. A combined thermoradiation-convective drying method is proposed, in which a combination of periodic irradiation of the dried material with convective drying takes place.
Day pasta ordinary (diameter 7 x 4.5 mm) from flour I grade recommended the following drying mode:
| Medium temperature (t C), °C .......................................... ................................................. 37 |
| Relative humidity of drying air, % ....................................................... ......70 |
| The speed of air movement over a layer of pasta, m / s .............................................. ...2.6 |
| The temperature of the irradiation generator (t g en), °C ....................................... ..................100 |
| The ratio of the duration of irradiation and resting (;), sec ...... 5: 100 |
| Distance from macaroni to emitters (double-sided irradiation), mm......................40 |
| Drying time (), hour ………………………………......................2.6 |
The experiments of F. Staff (USA) showed that when using infrared radiation, the drying time of short-cut pasta made from high-protein wheat and soy flour is significantly reduced. In this case, the products acquire a brown tint.
In the pasta laboratory of VNIIKhP (former TsNILMap), work was carried out to study the process of radiation drying of tubular pasta in suspended states. To do this, parallel to the pasta strands, panel-type radiators were installed, made in the form of cast-iron plates with spirals embedded in them. The temperature of the radiation generators was 150°C; the distance from the surface of the emitter to the product is 170 mm, the duration of exposure is more than 3 minutes.
For pasta of the "Straw" type (diameter 8 mm) from flour of the 1st grade (from durum wheat), the best results for combined thermoradiation-convective drying were obtained under the following modes:
preliminary thermoradiation-convective drying, consisting of three cycles; in each cycle, irradiation at t = 160 °C, carried out for 3 minutes, alternates with convective drying for 2 hours at the following parameters: t = 32 - 35 °C; φ = 85%; V= 0.5 m/s, while 7.5% of moisture is removed;
stepwise convective drying with increasing drying capacity of air:
t \u003d 32-35 ° С; φ = 85%; V = 0.5 m/s to W = 19-19.5%
t \u003d 32-35 ° С; φ = 75-80%; V = 0.5 m/s to W = 15%
t \u003d 32-35 ° С; φ = 67-71%; V = 0.5 m/s to W = 13%
The total drying time is 9.5 hours, which is 8.5 hours less than with convective drying without irradiation. The effectiveness of irradiation is evidenced by the fact that basically the duration of the process is reduced due to the initial “drying” (from 29 to 22%), in this zone the duration of drying is reduced by 5 hours, that is, by more than 50% of the total duration of the entire process . Characteristically, after preliminary irradiation, the drying process proceeds more intensively; it is obvious that the drying mode can be more severe than usual,
G. Hummel (England) notes that the use of infrared radiation is also possible for drying short-cut products. However, the use of lamps as generators increases the size of the installation.
With the combined drying method, the duration of the process can be reduced to 3 hours, however, the quality of the product deteriorates, and reducing the duration of the drying process to 1 hour causes a sharp deterioration in product quality.
Karasoni Laszlo and Harchittau Emmil (Italy) conducted a study on the possibility of using infrared radiation for drying pasta. In this case, panels were used at a distance of the product from the generator 80-100 mm; drying mode intermittent; irradiation 5-30 sec, rest 40 sec. During this period, the dough was cooled with air at room temperature. In this way, drying was carried out to equilibrium moisture content. However, it was not possible to obtain products without cracks. The efficiency of the drying plant was in the range of 4-6%. It has been established that all the work carried out to intensify the drying process can be combined into one direction: the duration of dehydration is regulated by the drying capacity of the air or the use of new methods of energy supply, while the "moisture-holding capacity" of the drying object (pasta) remains unchanged.
Reducing the "moisture-holding capacity" of raw pasta is possible with a change in their specific, physico-chemical properties. The essence of these changes lies in the fact that by pre-treatment of the object, the binding energy of moisture with the constituent components of the test is reduced. Thus, the products are prepared for the dehydration process.
Recently, the literature highlights the issue of finding a method for pre-treatment of the drying object, which allows to reduce the binding energy of moisture with the material. However, an effective method for reducing the binding energy of moisture with dry matter can be considered one that would allow, along with a reduction in the drying time, to obtain a finished product that meets all the requirements of the standard. In this regard, it became necessary to find a method for pre-treatment of pasta, which allows obtaining good quality products.
WAYS OF INTENSIFICATION OF DRYING OF PASTA
In Switzerland, hydrothermal treatment is supplemented by subsequent freezing of products at a temperature of minus 26 ° C for 15 - 25 minutes.
In the United States, it is proposed to use heat treatment with dry steam at a temperature of 101-180 ° C, previously "dried" products with infrared energy supply for 5-30 seconds.
In France, to speed up drying, raw pasta is boiled after pressing and then aged in ethyl alcohol, which gradually displaces moisture from them; after the total, the products are quickly dried, and the alcohol is regenerated.
A.S. Ginzburg, V.I. Syroedov, N.I. Nazarov recommend using surface-active substances (surfactants), for example, ethyl alcohol, hexane or toluene, which are characterized by a low coefficient of surface tension, in order to reduce the binding energy of moisture with the material and intensify the internal transfer of moisture.
MTIPP conducted research to test the following types of heat treatment of pasta: hydrothermal with washing the surface of products with cold (t = 15 ° C) or hot water (t = 100 ° C) and without washing followed by freezing and without freezing, as well as hygrothermal treatment, carried out according to the same options.
The data show that all types of pasta pre-cooking significantly reduce the overall drying time. Thus, drying pasta of standard humidity after hydrothermal treatment with washing in cold water for 5 minutes and subsequent freezing at a temperature of minus 25 ° C for 25 minutes was 177 minutes. The parameters of the drying agent were as follows: temperature 90 °C , relative humidity 30%. The loss of solids during cooking, the increase in volume, color and structure in the fracture met the requirements of GOST. However, the disadvantage of these methods is the sticking of products. To eliminate sticking, the products were washed with cold and hot water, frozen, and processed in a vibration field. However, this proved to be ineffective. At the same time, hygrothermal processing in cassettes, in comparison with hydrothermal processing, significantly reduces the duration of pasta drying. Thus, the duration of drying hygrothermally processed and frozen pasta was 115 minutes, and without freezing 90 minutes. At the same time, such indicators of quality as finished products from a distance, such as the loss of solids in the cooking water, the increase in volume, were within the requirements of GOST. However, partial adhesion of the products was still observed.
Analysis of the above data allowed us to conclude that hydrothermal treatment is superior to hydrothermal treatment.
Drying of pasta subjected to hygrothermal treatment in a suspended state on bastuns, with the parameters of the drying unit φ = 80%; t = 60 °С; V = 1 m / s, allowed to completely avoid sticking of products, the quality of which met all the requirements of GOST. Hygrothermal treatment was carried out at a constant initial moisture content of the products. The steam parameters also did not change. The influence of the duration (1-5 min) of hydrothermal treatment with an interval of 1 min on the drying process and the quality of products was studied. It has been established that the hygrothermal treatment of products has a significant impact on the drying process.
On fig. 1 shows the drying curves of pasta with and without hygrothermal treatment (τ so) of 2 and 5 minutes. The drying process was carried out at "rigid" constant parameters of the drying agent. The use of the "hard" mode reduces the time of dehydration of products not subjected to hygrothermal treatment from 18-24 hours to 13.6 hours. It should be noted that under industrial conditions, drying is carried out under “softer” modes. However, with a “hard” drying mode, the outer layers of the products dry out much faster than the inner ones due to the appearance of large moisture gradients and cracking of the pasta is observed both during the drying process and during their storage.
Fig.1. Pasta drying curves:
1 - without hygrothermal treatment; 2, 3 - with hygrothermal treatment for 5 and 2 minutes, respectively.
Hygrothermal treatment of products before drying significantly reduces the dehydration process, as it allows the use of "hard" drying modes without fear of cracks. In this case, two interrelated processes take place: thermal denaturation of proteins and modification of starch. The latter, under conditions of moisture deficiency, does not cross the border of gelatinization of the first row. Protein denaturation leads to a decrease in the binding energy of moisture with dough proteins and to the strengthening of the structure of the latter. So, the tensile strength of products not treated with heat is 320 g, and processed - 790 g.
Pasta, pre-heat-treated, did not crack during storage for 6 months or more. The drying curves presented in Fig. 1 show that the initial moisture content of products without processing and after it differs sharply. So, pasta with hygrothermal treatment has W = 54.6%, and without it - 47.5%. The first critical humidity (W) also differs significantly: in the first case it is 34%, in the second - 30%.
However, the moisture removal in the first period of drying for pasta after hygrothermal treatment is greater than for products without it. For heat-treated pasta, it is 20.6%, and for unprocessed - 17.5%. It should also be noted that the duration of the first drying period in the first case is less (55 min) than in the second (125 min).
The second drying period is significantly longer in the case of drying pasta without heat treatment (690 min vs. 480 min). With a given duration of hygrothermal treatment, the equilibrium moisture content of pasta changes slightly (with hygrothermal treatment W = 13%, without it -14%); at the same time, the relative humidity of the air is 80%, the temperature is 60 °С, the speed is 1.0 m/s.
Figure 2 shows the drying rate curves, the duration of which in the first and second periods is much longer for pasta subjected to hygrothermal treatment. Drying speed in the first period (N With) is greater for pasta that has undergone a 2-minute hygrothermal treatment and is 0.31% / min compared to 0.14% / min for products without treatment.
An increase in the duration of hygrothermal treatment from 2 to 5 minutes leads to an increase in the drying time by almost 2 times (see Fig. 1), which is explained by the deepening of the starch gelatinization zone, resulting in the formation of stronger moisture bonds with this dough component. The drying rate with 2-minute hygrothermal treatment both in the first and second periods is higher than with 5-minute hygrothermal treatment (see Fig. 2). A comparison of the drying curves and its speed during hygrothermal treatment in the range of 1-5 minutes shows that a 2-minute treatment is optimal in terms of the total drying time. By mathematical processing of experimental data, carried out on the BESM-6 computer, equations were obtained for the drying curves of pasta in 1 and 2 periods and the drying rate:
For the first period: (from W to W)
W = B - A; - A=N(1)
where W is the current humidity corresponding to 1 drying period, %;
W - the first critical moisture content of pasta, %;
W - initial moisture content of pasta, %;
Drying time in 1 period, min;
B, A - coefficients of the equation (B -%, A -% / min);
Drying rate, %/min;
Rice. 2 Pasta drying speed curves:
1, 2 - with hygrothermal treatment for 2 and 5 minutes, respectively; 3 - without hygrothermal treatment.
For the second period: (from W to W, with W tending to W)
W \u003d W + C exp (-m)
differentiating equation (2), we obtain the drying rate equation
M C exp (-m), (2)
where W is the second critical humidity, %;
W - equilibrium humidity, %;
W - current humidity corresponding to the 2nd drying period, %;
Duration of drying in the 2nd period, min;
С - equation coefficient, %;
m - exponential rate, 1/min;
Drying rate in the 2nd drying period, %/min.
Table 1 shows the numerical values of the coefficients of equation (1) and (2) of the drying curves and the drying rate of pasta depending on the parameters of hydrothermal treatment and drying.
Table 1
| Parameters of hygrothermal treatment |
Coefficients of equations |
|||||||
| 1 drying period |
2 drying period |
|||||||
BIOCHEMICAL CHANGES IN STARCH AND PROTEIN OF PASTA PRODUCTS AND THEIR TECHNOLOGICAL CHARACTERISTICS DURING HEAT TREATMENT AND DRYING
Kinetics of the process of drying hygrothermally processed pasta. In the industry for drying tubular pasta, a "soft" three-stage pulsating mode is used, often changing the drying capacity of the air.
The use of preliminary hygrothermal treatment of raw products made it possible to apply more "hard" modes with a constant drying capacity of air. As a result, cracking of products is eliminated, both during the drying process and during long-term storage. This is also facilitated by the introduction into the drying process of the final technological operation - the stabilization of products, which in its physical and chemical essence is similar to the conditioning of products.
The mode of drying with heated air (without pre-treatment with steam) is characterized by the following parameters: air temperature (); relative humidity (); air speed ().
With the introduction of hygrothermal treatment, a fourth parameter appears - the duration of hygrothermal treatment (). These parameters affect not only the drying rate, but also the critical equilibrium moisture content of the material, as well as the properties and quality of the product. Therefore, it is necessary to find a drying mode that, with the minimum drying time and the lowest energy consumption, will ensure high quality of finished products.
The kinetics of the drying process of pasta subjected to preliminary hygrothermal treatment was studied in the range of parameters: relative air humidity from 50 to 80%; air temperature from 50 to 80 °C; air speed from 0.5 to 2.0 m/s.
Studies have shown that the drying of hygrothermally processed pasta proceeds the more intensively, the lower the relative humidity and the higher the temperature and speed of the drying agent. However, it is possible to finally judge the values of the optimal humidity, temperature and speed of the drying agent only taking into account the quality indicators of the finished products. The quality of products was assessed according to the following indicators: acidity, color of products, strength on the Stroganov device, culinary properties (the amount of solids that pass into the cooking water; volume increase coefficient; increase in the mass of pasta during cooking; cooking duration). Changes were investigated: attackability of starch by amylolytic enzymes and protein substances by proteolytic enzymes; as well as the content of nitrogen in the cooking water and water-soluble nitrogen under the action of hygrothermal treatment.
Biochemical changes in starch and protein of pasta during hygrothermal treatment and drying. The structure of starch is of great importance in determining the properties of the pasta produced. The commodity and culinary properties of products depend on it. One of the ways to determine the degree of change in starch is to determine its attackability by amylases.
It is known that under mechanical or thermal action on starch grains, the rate of their attack by amylases increases. Starch subjected to processing (mechanical, thermal, etc.) is saccharified by β-amylase rather than unprocessed. At the same time, the attackability of starch increases most noticeably under the action of wheat β-amylase. Experiments were carried out to determine the attackability of starch by amylases under the action of hygrothermal treatment and at various drying parameters. The attackability of starch was determined by the increase in the content of reducing sugars formed under the action of the enzymatic extract of β-amylase (glycerol extract from wheat flour) in the dough at a temperature of 40°C for 1 hour; it was expressed in milligrams per 10 g of dry matter of the dough in terms of maltose. Changes in the biochemical characteristics of pasta during hygrothermal treatment and drying are given in Table 2.
From the data of Table 2 it can be seen that the attackability of starch by β-amylase in pasta without hygrothermal treatment was 100 mg per 10 g of dry matter of the dough in terms of maltose, and after processing the pasta with steam for 2 minutes increased to 236.5 mg i.e. .more than 2 times. Moreover, with an increase in the duration of hydrothermal treatment, the attackability of starch by β-amylase increased and with a 5-minute treatment was 253.5 mg. The increase in attackability is associated, therefore, with the partial gelatinization of starch during the heat treatment of products with steam, which is in good agreement with the slowdown in the drying rate with an increase in the duration of hydrothermal treatment. The parameters of the drying agent also influenced the attackability of starch-amylase. With an increase in its temperature from 50 to 60 ° C, the attack ability increased from 156 to 236.5 mg. A further increase in temperature led to the inactivation of β-amylase, which caused a decrease in starch attackability. Thus, this indicator at a temperature of 70 and 80 °C decreased to 190.5 and 166 mg, respectively. At a relative humidity of 60%, the attack rate was 219 mg, and at 80% - 236.5 mg. Starch attack by β-amylase at air speed m/sec: 0.5 - 167; 1.0-236.5; 1.5 - 225; 2.0 - 204 mg.
The index of starch attackability turned out to be sensitive to changes in relative humidity and speed of the drying agent. At a constant air temperature (C60°C), an increase in its relative humidity and speed up to 1.0 and/sec, the attackability of starch increased, which was explained by the deepening of its gelatinization due to more intensive heating of the products.
Hygrothermal treatment of products causes denaturation of gluten proteins, which become less soluble and lose their catalytic activity. The attack ability of protein substances by proteolytic enzymes was assessed by the accumulation of water-soluble nitrogen. From the results given in table. 2, it can be seen that the attackability of pasta protein substances without hygrothermal treatment was 39.0%, and with 2-minute steam treatment - 30.35%. With an increase in the duration of hygrothermal treatment to 5 minutes, attackability decreases to 27%. Thus, it has been established that thermal denaturation occurs as a result of hygrothermal treatment, which contributes to a decrease in the activity of protein substances. The drying process also causes significant denaturation of the protein even with mild heat treatment. In this regard, it is of interest to trace how the activity of protein substances changes depending on the parameters of the drying mode. Drying parameters can be recommended in terms of the attackability of protein substances.
table 2
| Duration of hydrothermal treatment |
Drying agent parameters |
Starch attack by wheat β-amylase, mg maltose per 10 g dry matter |
The attack of protein substances by the accumulation of water-soluble nitrogen, |
||||
| relative humidity |
temperature |
Speed |
|||||
Increasing the air temperature in the drying chamber has a different effect on the attackability of proteins. Thus, with an increase in temperature from 50 to 70 °C, the attackability of protein substances increased from 29.6 to 31.6%, a further increase in temperature reduced the attackability to 25.6%. Changing the speed of the drying agent also has a different effect on the attackability of protein substances. At a speed of m / s: 0.5 - 26.96; 1.0 - 30.3; 1.5 - 34.05, and at 2.0 - 32.7%. Considering the influence of the parameters of the drying agent on the attackability of protein substances, we see that when drying hygrothermally treated tubular pasta, the optimal air temperature is 60-70 ° C, the air speed is 1.0 - 2.0 m / s. At the same time, changes in the protein-proteinase complex in pasta were tested using hygrothermal treatment. At the same time, the amount of total nitrogen in the cooking water and water-soluble nitrogen were determined. As a result of hygrothermal treatment, the amount of nitrogenous substances in the cooking water decreased. So, with an increase in temperature from 50 to 70 °C, the attackability of protein substances increased from 29.6 to 31.6%, a further increase in temperature reduced the attackability to 25.6%. Changing the speed of the drying agent also has a different effect on the attackability of protein substances. At a speed of m / s: 0.5 - 26.96; 1.0 - 30.3; 1.5 - 34.05, and at 2.0 - 32.7%. Considering the influence of the parameters of the drying agent on the attackability of protein substances, we see that when drying hygrothermally treated tubular pasta, the optimal air temperature is 60-70 ° C, the air speed is 1.0 - 2.0 m / s. At the same time, changes in the protein-proteinase complex in pasta were tested using hygrothermal treatment. At the same time, the amount of total nitrogen in the cooking water and water-soluble nitrogen were determined. As a result of hygrothermal treatment, the amount of nitrogenous substances in the cooking water decreased.
Change those X technological characteristics of finished products. The drying process significantly affects the quality of the finished product, and the choice of optimal parameters depends on the quality indicators of the finished product. The taste qualities or defects of pasta are judged by their acidity, which, according to GOST, should not exceed 3-4 degrees. The color of pasta should be yellowish, characteristic of products made from flour obtained from durum wheat. A number of factors influence the color of finished products; raw material color, process conditions, etc.
As studies have shown with the use of hygrothermal treatment, the color of the products changes dramatically, they acquire a pleasant amber-yellow color; at the same time, the surface of the pasta becomes glossy and their strength increases significantly. The strength of products (determined on the Stroganov device) without hygrothermal treatment with a “hard” drying mode is lower than the GOST value and is equal to 606 g. With the use of hygrothermal treatment, the strength of pasta increases sharply and reaches 2070 at 2 minutes. Another important characteristic of the consumer value of pasta are their properties during cooking: the duration of cooking until cooked, the increase in the mass of cooked products, the loss of solids in the cooking water, the increase in the volume of pasta during the cooking process. All these indicators were determined by standard methods. The amount of solids that passed into the cooking water with the use of hygrothermal treatment decreased and amounted to 4.21% compared to 5.19% (without steam treatment), while the volume increase coefficient slightly increased from 3.28 to 3.32 times and was within the allowed limit. The increase in the mass of pasta during cooking decreased in pasta produced using hydrothermal treatment (for 2 minutes), from 173 to 168%. The relative humidity of the air also affected the brewing performance. Thus, an increase in the relative humidity of the air from 50 to 80% contributed to a decrease in the amount of dry matter passing into cooking water, a decrease in the volume increase coefficient (from 3.5 to 3.32 times) and an increase in the mass of pasta during cooking. The temperature and speed of the drying agent had little effect on the brewing performance.
We also note that the use of hygrothermal treatment helps to reduce the duration of cooking products until ready from 20 to 10 minutes. The appearance of cracks in the products was fixed within 3-4 hours after drying.
Considering the main technological indicators of pasta, we can conclude that the use of hygrothermal treatment significantly improves the quality of the finished product. Conditioning pasta. The use of "hard" drying modes will cause the risk of cracking on the surface and in the deep layers of products, even under conditions of significant strengthening of the structure of the pasta tube. The reasons for the formation of cracks are uneven drying, shrinkage processes and the occurrence of shear stresses that exceed the maximum allowable values.
The stronger the structure, the lower the probability of cracking, however, a full guarantee of preventing cracking is possible when switching to "soft" drying modes or applying conditioning (stabilization) of products at the final stage of drying when they reach a moisture content of 18%. The purpose of conditioning (stabilization) is to relieve the stresses that have arisen during the drying of pasta in the "hard" mode.
Conditioning was carried out as follows: pasta in the working chamber of the installation was treated with a steam-air mixture with the required parameters. At the same time, the dried products were moistened to about 14%, and the outer layers reached a higher moisture content than the inner ones. As a result, the wet layers were stretched and shear stresses were removed. After conditioning, the products were exposed to air. During stabilization, the products were cooled to room temperature, and their humidity reached a standard value.
CHANGES IN STRUCTURAL AND MECHANICAL PROPERTIES OF PASTA SUBJECTED TO HYGROTHERM TREATMENT
After hygrothermal treatment, the products are hardened though. But they remain quite flexible. Cracking and warping of pasta is due to uneven distribution of moisture inside the material, resulting in a volumetric stress state. Normal stresses due to tension and shear stresses due to shear deformations can exceed the maximum allowable values and cause destruction of the structure.
It is of interest to find out the main rheological characteristics of pasta dough subjected to hygrothermal treatment at different humidity, since they determine the normal and shear stresses in the material,
NOT. Netushil conducted tensile tests on pasta dough. However, with the use of pre-hygrothermal treatment, this method of determining rheological characteristics cannot be applied, because, starting from a moisture content of 34%, the products become quite strong, and the sample clamps used do not allow tensile testing: the pasta dough slips out of the clamp and the break does not occur in the middle, as required by the technique, but near the clamped end of the specimen. The dried products were tested for compression. For the study, a sample of pasta was taken with dimensions (mm): length - 50, outer and inner diameters, respectively, 7 and 4.5.
Changing the dimensions of the sample somewhat changes the results of the test, which is explained by the influence of the scale factor.
The main criteria for evaluating the structural and mechanical properties are the strength and the characteristic parameters of the relaxation process (elastic-kinetic and rheological). In the works of I.S. Melnikova and N.E. Netushil described the influence of the moisture content of products on the change in the process of drying plastic-elastic deformations. However, there is no data on what adjustments to this relationship can be made by preliminary hygrothermal treatment of the drying object. To study this issue, MTIPP manufactured a special device for measuring the load at a constant strain rate on compression of a pasta tube in the longitudinal direction.
The device (Fig. 3) consists of an electric motor, which, using a belt drive, drives the screw (the gear system from the electric motor to the screw allows you to change the speed in a ratio of 1:2:4)
Rie.Z. Scheme of the device for studying the rheological characteristics of pasta during the drying process:
1 - electric motor; 2 - belt drive; 3 - screw; 4 - elastic element; 5 - oscilloscope; 6 - strain gauge
The load applied to the pasta tube in the axial plane along the entire length of the generatrix perpendicular to the axis is transferred to the elastic element - a steel beam of rectangular cross section, lying on two supports. Under the action of the load, not only the beam is deformed, but also the resistance strain gauges inclined on it and assembled into a bridge circuit. From the measuring diagonal, the current is passed through the amplifier to the oscilloscope and recorded on the pasta tube compression diagram. On the y-axis of this diagram, the load is plotted, and on the abscissa, the absolute compression of the tube, proportional to the loading time. The compression test was carried out at the following stages of the technological process: after pressing after hydrothermal treatment, at certain intervals during the entire drying process. The applied load varies from zero to the amount of compression or destruction of the sample. Between the applied load and the internal forces in the sample at each moment of time, equilibrium is maintained. The relationship between stress σ and strain ε of a pasta sample is plotted on an oscillogram.
According to the diagram of change σ = f (ε) at different values of dough moisture, one can trace the change in the main structural and mechanical parameters both during hydrothermal treatment and during drying.
In table. 3 shows the results of the main structural and mechanical parameters of the pasta tube. As can be seen from the data in Table. 3, preliminary hygrothermal treatment significantly changes the rheological parameters. So, - increases by an order of magnitude from 8 kPa to 23 kPa, the maximum compressive stress m ah, shear stress ks, the modulus of elastic deformation E (conditional) increases by 2 times, and the modulus of elastic-plastic deformation E decreases from 727 kPa to 5 77 kPa, which once again confirms the conclusions about the strengthening of the structure of products produced using preliminary hydrothermal treatment.
Technology of bread, confectionery and pasta Table 3
The rheological characteristics undergo a significant change in the process of further drying, while two periods are distinguished (1 period corresponds to a constant drying speed, 2 - a decreasing speed). In the first period, all rheological characteristics remain unchanged, and when the moisture content W = 33.2 is close to the value of the critical moisture content, the main structural and mechanical parameters begin to increase. With a moisture content of 33.2, the value of the modulus of elastic-plastic deformations E approaches the value of the conditional modulus of elasticity E, and at the same time, the plastic deformation of the product attenuates, mainly acquiring elastic properties.
On pic . 4 shows the curves of changes in the maximum voltage of the pasta tube during the drying process. The curves have two characteristic regions. The inflection point lies on the boundary of the transition from the first to the second drying period, which at the same time corresponds to the transition from the plastic state of the substance to the elastic one. In the experiments, the initial moisture content and the maximum compressive stress of the products are the same W = 45% , m ah \u003d 105 kPa. As a result of hygrothermal treatment, the products are moistened to W = 54.6%, and the maximum compressive stress increases to m ax = 200 kPa. Already from this moment, the difference between the values of the maximum compressive stress of products subjected to hygrothermal treatment and without it is 100 kPa, and by the end of drying at W = 16%, this difference increases to 750 kPa,
The transition points from the straight section to the curvilinear one do not match either in terms of moisture content or in terms of the maximum compressive stress. The transition to the elastic state in pasta subjected to hygrothermal treatment occurs ahead of time (by 4–5%) compared to products without processing. From the above graphs it follows that the hygrothermal treatment of products leads to their significant hardening. During the drying process, many materials, including pasta, reduce their size, i.e. shrinkage occurs. If the drying process is not carried out correctly, the pasta will crack. The reason for the latter is the uneven shrinkage of the layers of the dried material. Intensified modes of pasta drying are limited by their shrinkage.
Hygrothermal treatment leads to strengthening of the structure of pasta, caused by protein denaturation. In turn, the denaturation of proteins contributes to a decrease in the size of the material. But hygrothermal treatment increases the mass of the substance by moistening the products. This explains the invariance of the size of pasta, subjected to steam treatment.
Rice. 4. Curves of changes in the maximum compressive stress of the pasta tube during the drying process:
1 - without hygrothermal treatment; 2 - with a two-minute hygrothermal treatment
However, during the drying process, the nature of the shrinkage of the pasta tube of hygro-thermo-treated pasta is different from that of conventionally cooked pasta. According to the experimental data, linear shrinkage coefficients for two drying periods and , relative shrinkage δ, volumetric shrinkage coefficients β and volumetric shrinkage δ were established. Comparing the values of the coefficients of linear and volumetric shrinkage of pasta without hygrothermal treatment and with it, it can be seen that steam treatment helps to reduce the coefficient of linear shrinkage. The volume shrinkage coefficient also decreases with the use of hygrothermal treatment. Such a change in linear and volumetric shrinkage due to the use of hygrothermal treatment makes it possible to dry pasta in a "hard" mode, since the possibility of cracks is reduced.
But the risk of cracking still remains, and especially in the second stage of drying. As a criterion for assessing the risk of crack formation, the Kirpichev criterion can be taken:
K 
(3)
where is the mass flow;
defining size;
Average moisture content corresponding to the Fourier criterion
It is important to note that with the conventional drying method, the maximum allowable value of the Kirpichev mass transfer criterion for pasta is about 0.6 . The use of pre-hygrothermal treatment contributes to an increase in strength and leads to the fact that the products are able to withstand higher shear stresses. Therefore, the maximum allowable value of the Kirpichev mass transfer criterion for pasta that has undergone preliminary hygrothermal treatment increases to 1.3 , which indicates a reduction in the possibility of crack formation.
As can be seen from the data obtained, hygrothermal treatment has a significant impact on the structural and mechanical characteristics of pasta.
The change in structural-mechanical parameters in the strengthening of the structure of products is one of the main factors in intensifying the drying of products subjected to preliminary hygrothermal treatment, the products become "susceptible" to maintaining a "hard" drying mode.
MASS TRANSFER CHARACTERISTICS AND EQUILIBRIUM AND CRITICAL HUMIDITY OF PASTA
The mass transfer kinetics of a substance in wet materials is determined by the mass transfer potential difference. The molecular-kinetic theory of heat and mass transfer phenomena assumes that under isothermal conditions the moisture flux density is directly proportional to the gradient of the mass transfer potential:
q kg/mh, (4)
where is the mass transfer potential gradient, ;
The coefficient of mass conductivity, which determines the ability of a wet material to transfer moisture with a magnitude of the potential gradient, kg/m.h.;
Degree of mass transfer.
Since the thermodynamic mass transfer potential under isothermal conditions is an unambiguous function of moisture content, the mass transfer potential gradient can be expressed in terms of the moisture content gradient:
where is the moisture content gradient kg·moisture/kg·SV·m;
Specific moisture capacity of a wet body, kg moisture/kg SV;
Taking into account formula (5), the basic law of isothermal mass conductivity can be represented as follows:
q 
(6)
de - density of an absolutely dry body, kg SV / m;
The coefficient of internal mass transfer (depends on temperature and moisture content), which characterizes the properties of the body in relation to the intensity of the development of fields of the mass transfer potential or the inertial ability of the body to external water disturbances.
Therefore, the intensity of drying mainly depends on the coefficient of internal diffusion of moisture. An analytical determination of the internal mass transfer coefficient from the drying curves and the drying rate was carried out according to the following formula:
(7)
where R is the characteristic body size, m;
Drying rate, %/m;
Coefficient of external mass transfer, m/h.
Equilibrium humidity, kg/kg.
(For pasta tube, if R=3.5mm,=2.25mm, ratio=0.625mm)
The nature of the change in the coefficient of internal diffusion of moisture during drying with and without hygrothermal treatment is similar. In the first period of drying, it remains constant, and during the period of decreasing drying rate, it changes slightly, but decreases by 2 times in absolute value,
During the period of constant velocity, moisture will move as a liquid (selective diffusion of osmotically retained moisture), the temperature of the material will be constant and equal to the temperature of the wet bulb.
When the first critical point corresponding to hygroscopic moisture is reached on the surface of the material, the drying rate will begin to decrease, and the movement of adsorption-bound moisture inside the material will mainly occur in the form of steam. It should be noted that in the second period the speed decreases according to a linear law, this pattern is in accordance with the change in the internal diffusion coefficient during this drying period. The coefficient of external moisture exchange changes similarly. Figure 5 shows a diagram of changes in the coefficients of external moisture exchange and internal mass transfer for pasta subjected to preliminary hydrothermal treatment and dried according to the commonly accepted technology. These coefficients, both in the first and second periods, are higher for products that have undergone preliminary hygro-thermal treatment, which once again indicates the intensification of the drying process.
Rice. 5. Diagram of changes in the coefficients of external moisture exchange and internal mass transfer a m of pasta with the introduction of hygrothermal treatment:
1,2 - drying of pasta, respectively, without heat treatment and with heat treatment
In table. Figure 4 shows the coefficients of external moisture exchange and internal mass transfer for various regime parameters of hydrothermal treatment and drying. The coefficients of internal diffusion and external moisture exchange depend on the duration of hygrothermal treatment and on the parameters of the drying mode.
Table 4
| Parameters of hygrothermal treatment |
Moisture coefficients of pasta |
||||||
From the data of Table 4 it can be seen that the largest values of these coefficients are observed during 2-minute hygrothermal treatment. The coefficients of external moisture exchange of internal diffusion decrease with an increase in the relative humidity of the air, a decrease in temperature and a decrease in the speed of the drying agent.
Equilibrium and critical moisture content of pasta. By the method of analytical processing of drying curves and drying rate, the values of equilibrium and critical moisture content of pasta were obtained (Fig. 6).
It should be emphasized that heat treatment leads to some decrease in the equilibrium moisture content of the finished product. This factor is of practical importance, indicating an increase in the stability of pasta during storage.
Rice. 6. Graph of the effect of heat treatment on the first critical point W
and equilibrium humidity W
In addition to the results obtained, the effect of heat treatment on the first critical moisture content of pasta was studied (see Fig. 6). It can be seen from the graph that the first critical moisture content in products subjected to preliminary hygrothermal treatment increases (especially with a 2-minute treatment). This is important for practical technology, since the transition from the plastic state of matter to the elastic state is associated with this point. The first critical point shifts upward for products prepared using the new technology.
INSTALLATION FOR DRYING PASTA PRODUCTS USING NEW TECHNOLOGY AND JUSTIFICATION OF THE FEASIBILITY OF INTRODUCING A NEW DRYING METHOD
At present, dryers for hanging drying of long pasta are known. These include the dryer in the line "LMB" and foreign - firms Braibanti (Italy) and Buhler (Switzerland). These continuous dryers are equipped with preliminary, final, and stabilization drying chambers. Drying of long tubular products on these installations is carried out in "soft", three-stage pulsating modes, with a long time (18-24 hours) for drying. In addition, the listed dryers are bulky, their length reaches 30-45 m.
In connection with the use of preliminary hygrothermal treatment before drying and conditioning at the end of it, it became necessary to create a dryer design that included new technological operations.
Figure 7 shows a diagram of an installation for drying long-tube pasta in a suspended state. The installation consists of chambers: pre-hygrothermal treatment, storage, dryer, conditioning, transitional won and a chamber for stabilizing dried products. The dryer is equipped with an air supply chamber and devices for supplying steam. Bastuns with a semi-finished product after the press enter the pre-hygrothermal treatment chamber, where they are exposed to a mixture of air and steam for 2 minutes. Then the products enter the storage chamber, after which they are sent to the drying chamber, where they move along the tiers from the bottom up. When the products reach the upper tier, their moisture content reaches 13%. To relieve internal stresses, the dried products are sent to the conditioning chamber, where they are moistened to a moisture content of 16% in a steam-air environment for 1-2 minutes. After the conditioning stage, the products are fed into the stabilization chamber, where they cool down and dry to a standard humidity of 13%.
The duration of the process of hygrothermal treatment and drying of pasta for different types of flour in the proposed drying plant reaches 8 - 10 hours. Thus, the use of a new technology for the preparation of long-tube pasta makes it possible to reduce the duration of the drying process by 3 times; apply "hard", constant parameters of the drying agent; reduce overall installations; improve product quality.
Fig.7. Drying plant layout
1, 2, 3, 4, 5, 6 - chamber, respectively, hydrothermal treatment; resting, drying, transition zone, conditioning, stabilization of dried products; 7 - opening for unloading finished products; 8 - chamber for air supply; 9 - device for supplying steam; 10 - opening for loading products
Justification of the expediency of introducing a new drying method. In table. 5 shows a comparison of the technical characteristics of the existing LMB line and the one being reconstructed using the new method.
From the data in Table. 5 it follows that the introduction of a new drying method can significantly reduce the drying time and reduce the dimensions of the dryer (in length) by 2 times.
Table 5
The developed drying plant makes it possible to place a modern automatic line for the production of pasta in existing pasta factories during their reconstruction.
Other benefits of implementing the new drying method are as follows:
Breaks in the initial stage of drying are eliminated due to a significant strengthening of the structure of raw billets (blockage of drying plants by breaks of strands during hanging drying of products from weak flour is practically excluded);
The taste of products improves (obviously, as a result of a hard drying regime, a reaction of melanoidin formation occurs); culinary properties increase compared to ordinary pasta: they boil faster, with a long stay in boiling water, the products retain their individuality; the amount of all extractive substances passing into the cooking water is reduced.
By reducing the duration of the technological process (by 3 times), it is possible to increase the volume of output per unit of drying area per day also by 3 times. Since the occupied area for the new line will be 2 times less than the area required for the installation of the LMB line, it seems possible to place 2 new lines that implement the drying process according to the proposed method. In this regard, the output increases by 6 times. However, the use of a new drying method based on hydrothermal treatment leads to a slight increase in steam consumption per hour, but in general, this economic indicator in terms of the total drying time will be reduced from 5750 to 2790 kg. The air consumption for the entire drying period will also be reduced by 52,000 m³.
Thus, the cost of pasta will decrease due to the reduction of depreciation deductions for the consumption of air, electricity and steam.
An analysis of literary sources shows that at present there are two directions in the intensification of the process of sushi pasta:
Preliminary hydrothermal treatment of the semi-finished product before drying;
Addition of surface-active substances (surfactants) to pasta dough.
It should be noted that the first method of intensifying the drying process was most widely used.
MTIPP has developed a technology for a continuous drying process with a "hard" mode of long-tube pasta, which is distinguished by the use of preliminary hygrothermal treatment and conditioning of products.
It has been established that hygrothermal treatment of raw products in combination with other technological drying factors significantly improves the totality of quality indicators of finished pasta, strength and fracture structure, appearance and their culinary properties.
Based on the developed technological modes of hygrothermal treatment, drying and conditioning of pasta, a scheme of a new drying plant is proposed in which the drying process is reduced to 8-9 hours while improving the technological and structural-mechanical properties of finished products.
By reducing the duration of the technological process by 3 times, it seems possible to increase the volume of products produced per unit of drying area per day also by 3 times, and reduce the cost of pasta by reducing depreciation: air, steam and electricity consumption.
LITERATURE
1. Taranov I.T. Convective multi-stage modes for drying pasta in flat cassettes. "Kharchova Promislovist". K., 1973. 2, pp. 42-46.
2. Chernov M.E., Polyakov E.S., Burov L.A., Savina I.M. Drying pasta in oscillating, rotating, cylindrical cassettes. (Information). CINTIPishcheizdat, M., 1971.
3. Kaloshina E.N., Demchenkova E.A., Divtsivadze G.V. Influence of various methods of heat treatment on the quality of pasta. Sat. scientific works ZIST department. "Commodity of foodstuffs". M., 1973.
4. Ginzburg A.S., Kaloshina E.N. Study of the drying kinetics of long tubular pasta. "Bakery and confectionery industry". "Food industry" 1, 24-25, M., 1973.
5. Ginzburg A.S. Fundamentals of the theory and technology of food drying. Publishing house "Food industry", M., 1973 .
6. Kaloshina E.N. Study of the drying process of long tubular pasta. Diss. for an apprenticeship degree Ph.D., M., 1973.
The closer the summer, the more the desire to lose weight and put yourself in order grows. But for those who ate pasta, sausages and sandwiches in a hurry for a long winter, it is difficult to reorganize in a new way. Most fitness trainers agree that there is no drying pasta. However, nutritionists have a different opinion.
Arguments for and against dried pasta
Opponents of pasta give the following arguments for refusing them:
- high glycemic index (rapidly increase blood sugar);
- the presence of gluten;
- high calorie.
Now only diabetics and nutritionists without deep knowledge pay attention to the glycemic index. According to them, when a lot of glucose enters the blood, our body, striving for a constant composition, can only utilize its excess into fat. Because high GI is bad for them. However, for such a scenario, the glycogen depots of the liver and muscles must be overfilled, which does not happen on a diet.
Gluten-free diets do not contribute to drying in any way (but do not interfere), they are needed only for people with celiac disease.
As for the calorie content, in 100 grams of boiled pasta, buckwheat and rice, it differs by no more than 5-10 calories. It is believed that foods with a higher glycemic index saturate for a shorter period, but the assimilation of food and subjective hunger / satiety from it depend not only on GI. Someone is hungry after a plate of buckwheat, and after the same, but pasta is full. There is no problem if you eat pasta with chicken rather than rice with breast, but at the same time meet your daily carbohydrate requirements.
What kind of pasta can be and how to cook them
Those who follow a diet face another danger of pasta: this product contains very few biologically active substances. On drying, the amount of food is limited, so it must have a high nutritional value, satisfying the needs for vitamins and minerals as much as possible. In order not to dry up to beriberi, you should choose pasta:
- from whole grain flour (whole grains contain more B vitamins), despite their unappetizing grayish or brown color;
- with additives - tomato, spinach, buckwheat, etc.
To preserve the useful components, they must be undercooked - served al dente.
Losing weight and drying is not a reason to completely abandon the usual products. Rather, the reason is to reconsider their quantity in the diet and methods of preparation.
Drying is one of the ways to preserve pasta dough, which consists of hydrophilic polymeric substances. If moisture is not removed from it, then microbiological, biochemical and other processes will develop, which will quickly lead to spoilage of the product.
Pasta dough releases moisture very slowly when dried. To control the dehydration process, it is necessary to take into account the totality of the properties of pasta dough, remembering that the main task of drying technology is to obtain a high quality product with minimal energy and labor costs.
Drying pasta, like drying any other capillary-porous materials, proceeds in two periods. The first is characterized by a constant speed and is due to the intensive removal of moisture, less strongly associated with starch. In the second period, characterized by a decreasing rate of drying, dehydration of the protein part of the products occurs, which holds moisture more firmly than starch.
Properties of pasta as an object of drying. Raw pasta is sent for drying at a moisture content of 30-32.5%. According to the classification of P. A. Rebinder, raw pasta that has passed the pressing stage belongs to coagulation structures, which are characterized by the presence of an elastic frame formed by the forces of intermolecular adhesion of protein molecules. Such structures show plasticity, elasticity and thixotropic properties. With dehydration, coagulation structures gradually lose their plastic properties; at the same time, their elasticity increases, as a result of which the structure is strengthened, and by the end of drying, they become a solid brittle body.
Pasta, when dried to a certain limit, retains the properties of plasticity, and starting from a moisture content of 25-20%, the elastic properties gradually overlap the plastic ones.
The kinetics of dehydration of pasta dough is characterized by extremely slow migration of moisture in the thickness of the product. Due to this, the replacement of plastic deformations by elastic ones proceeds extremely unevenly: on a dried surface, elastic deformations can reach the limit value, while the deep layers remain plastic. The end result of structural changes during drying is a decrease in the volume and linear dimensions of products.
Thus, the following properties are most pronounced in pasta dough during drying:
linear and volumetric shrinkage, which, under unforgiving drying conditions and a large unevenness of the moisture field, can cause cracking and distortion of products. The ability to crack and warp products is retained after drying;
low moisture conductivity, causing the internal transfer of moisture to lag behind moisture transfer to the environment and causing uneven humidity fields;
thermal denaturation of proteins and partial gelatinization of starch at high temperatures (dryer VIS-2), leading to a decrease in strength and a deterioration in the color of products;
two forms of moisture bonding: adsorption and osmotic, and the adsorption-bound moisture moves in the form of a vapor, the rest in the form of a liquid;
stronger moisture retention by dough proteins compared to hygroscopic starch due to the greater hydrophilicity of proteins. In the first period of drying, dehydration is more intense due to the fact that starch loses moisture first.
Modes of convective drying of pasta. The term "drying mode" is understood as a set of "parameters of drying air (temperature, humidity, speed), drying duration, the presence of periods of drying and dampening, their duration and frequency of alternation.
The drying modes used in the pasta industry are varied. When choosing a mode, it is necessary to take into account the above technological properties of pasta dough. In order to avoid distortion and cracking of the product, one should strive for its uniform drying both in cross section and in length. The ideal mode is one in which the internal mass transfer of moisture will not lag behind the moisture transfer from the surface of the products. It is difficult to implement such a regime, since during drying a significant moisture gradient is formed in the mass of dried products, in which the supply of moisture from the deep layers lags behind its evaporation from the surface of the product. Therefore, it is very important to maintain such a gradient value at which the drying intensity would be optimal.
In the initial stage of drying, the moisture gradient is minimal, and then its value increases. It follows from this that hard modes are possible at the first stage of drying, and sparing ones at the subsequent stages.
The following rule applies to pasta dough: as long as it is plastic, it can be dried quickly (stresses and the resulting cracking may not be observed, even if the difference in moisture content in the center and on the surface is significant).
For pasta, the most common two drying modes:
three-stage or pulsating mode;
continuous, at a constant drying capacity of the air.
In each mode, the main goal is to prevent the occurrence of large moisture gradients that are dangerous for cracking products.
Three-stage mode, judging by the name, consists of three stages. First stage - pre-drying. Its purpose is to stabilize the shape of raw products, preventing them from souring, molding and stretching. Drying lasts from 30 minutes to 2 hours and is carried out under relatively strict conditions. During this time, one third to one half of the moisture is removed from the amount that should be removed from the pasta. Such intense dehydration in a relatively short time is possible only at the first stage of drying, when the pasta is still plastic and there is no danger of cracking.
The second stage is called softening.. By increasing the relative humidity of the air, the crust is softened - the surface layer is moistened, as a result of which the humidity gradient decreases and the stresses that have arisen dissolve. This process is best carried out at relatively high temperatures and relative humidity, at which the rate of moisture diffusion increases and the duration of tempering is reduced.
Third stage - final drying- is carried out in a soft mode, since the products are in the area of elastic deformations. During this period, the rate of evaporation of moisture from the surface should be commensurate with the rate of its supply from the inner layers to the outer. At this stage, drying usually alternates with softening.
To some extent, this mode is similar to the method of drying tubular products in cassettes in non-calorific dryers. The fan is driven in a reverse way. With the help of a time relay, the electric motor periodically reverses the rotation of the fan. Drying is carried out according to the cycle: 1) direct direction of air blowing; 2) a short stop of the engine, corresponding to the stage of softening; 3) reverse blowing direction. The entire cycle lasts 30-40 minutes, and the duration of the entire cycle and its individual phases can be adjusted using the same time relay.
Continuous drying at a constant drying capacity of the air (mode of the second type) is extremely simple in terms of adjusting the parameters of the air and the process as a whole. In this mode, the parameters of the air at the inlet to the dryer remain approximately constant from the beginning to the end of drying.
A major disadvantage of this mode is that drying has to be carried out with a high drying capacity of the air. This mode can be used for products that are most resistant to deformation: short-cut and soup fillings. Drying them occurs in a shorter time than long-tubular; sizes are smaller. They are better amenable to comprehensive air blowing due to pouring. Nevertheless, it is desirable to dry short-cut products in a soft mode, since the structural and mechanical properties of the dough remain the same for these products.
A new way to dry pasta. The method was developed at the Moscow Technological Institute of the Food Industry by E. N. Kaloshina and G. V. Tsivtsivadze under the direction of N. I. Nazarov. The essence of the method lies in the special preliminary preparation of these difficult-to-dry products: during the drying process, a new simple technological operation is introduced - scalding of products with a steam-air mixture - hygrothermal treatment.
Until now, the problem of intensifying the drying of capillary-porous colloidal materials, which include pasta, has been solved by increasing the drying capacity of air. For pasta, this path turned out to be inefficient. The authors of the method took a different path - changing the properties of pasta as an object of drying. After hygrothermal treatment, the products are subjected to hard drying and conditioning at the end of dehydration, which ensures the relaxation of internal stresses in the finished products. Hygrothermal treatment of products before drying significantly reduces the drying time, as it significantly changes their rheological and physico-chemical properties, as a result of which the products become able to withstand severe dehydration conditions without cracking. During this treatment, two interrelated processes take place: thermal denaturation of gluten proteins and modification of starch, which, under conditions of moisture deficiency, does not cross the border of gelatinization of the first kind. Both processes lead to a decrease in moisture hydration by dough proteins and to a strengthening of its structure.
Studies have shown that hydrothermal treatment causes a 2-fold decrease in the coefficients of linear and volumetric shrinkage and an increase in the same number of times in the coefficient of crack formation (the so-called Kirpichev criterion), the strength indicators of finished products increase by 2-3 times. This heat treatment, in combination with other technological methods, makes it possible to reduce the drying time of tubular products from 20-24 hours to 8-10 hours and at the same time improve the combination of biochemical and technological qualities of finished products: strength, fracture structure, color, appearance, culinary properties. The duration of cooking products was reduced by half.
hygrothermal treatment - temperature and relative humidity of the steam-air mixture, respectively, 100 ° C and 98%; duration - 2 min;
drying - temperature and relative humidity of the drying agent, respectively, 60-70°C and 70-80%; air speed 1.0-1.5 m/s;
conditioning (stabilization) - temperature and relative humidity of the steam-air mixture, respectively, 90-100 ° C and 98%; duration - 1 min.
Industrial drying of pasta. In domestic and foreign industry, only convective atmospheric drying of pasta is used. Apparatuses and installations in which drying is carried out are divided into two groups: continuous conveyor and periodic.
The group of non-mechanized installations consists of two types of dryers: chamber and cabinet. The latter are widespread in the USSR.
Cabinet dryers replaced chamber dryers and were the result of their development. All cabinet dryers are characterized by a small capacity, which allows drying products of the same type at a certain moment. Products intended for drying are loaded into mobile trolleys, which are then fed into the drying plant. In cabinet dryers, it is possible to dry tubular products in cassettes and in a suspended state, short-cut products - in bulk; noodles and vermicelli - on frames and in a suspended state - on bastuns.
There are mainly two types of cabinet dryers: without air heating and with air heating (heater). The former are used for drying tubular products and hanging drying, the latter for drying short-cut products. Due to the widespread introduction of continuously operating conveyor dryers, cabinet-type calorific units are not currently produced in our country, but they are still in operation at the factories.
As an example, in fig. 1 shows a diagram of the VVP cabinet dryer, which is still widely used in our pasta factories.
Rice. 1. Scheme of the GDP dryer:
1 - drying chamber; 2-cassettes; 3 - fan casing; 4 - bypass distribution channel; 5 - TsAGI-700 fan on the motor shaft.
The VVP dryer is made of wood: a block frame, plywood sheathing. The front side of the cabinet is open for loading cassettes or frames. The correct installation of cassettes or frames is ensured by restrictive bars. An electric motor (power 1 kW, rotation speed 1400 rpm) with an vane fan 5 mounted on its shaft is placed on the ceiling of the cabinet. The electric motor is reversible; the fan wheel is placed in a branch pipe through which air is directed to a bypass distribution channel 4 formed by the rear wall of the cabinet and cassettes or frames with drying products. Reversing is carried out automatically every 30-60 minutes, depending on the assortment of the dried product.
The cabinet is designed for 190 double cassettes 500 mm long, 365 mm wide and 45 mm high. Three rows of cassettes are placed along the width of the apparatus, two rows along the length, and 40 rows along the height. When these apparatuses were used for drying short-cut products, 80 frames of 1100X700X45 mm were placed in them. The capacity of the device is 600 kg (for ready-made pasta).
The VVP dryer has the VVP-1 model differing in the sizes. Drying cabinet capacity 300 kg (120 cassettes). VVP dryers are usually installed in blocks of two along the front and in two rows close to the rear walls; Thus, there are 4 cabinets in the block. The cabinets along the front form the corridors of the drying shop, along which the free oncoming movement of loaded and empty trolleys is ensured.
Continuously operating automated dryers in the domestic and foreign pasta industry are used for drying long-tubular products in a suspended state on bastuns and short-cut and stamped products on belt conveyors. The French company Bossano produces tunnel dryers in which tubular products such as pasta are dried in rotating cassettes. Two such lines will be installed at pasta factories in the USSR.
Tunnel dryers for hanging drying, manufactured by the Rostov-on-Don Machine-Building Plant, are part of the LMB, LMV and LMG production lines, which differ in the daily output of presses and dryers. LMB lines have a capacity of 500 kg/h, LMG -1000 kg/h. The LMG production line includes a drying plant, shown in the figure in the section on the technological scheme for the production of pasta:
preliminary (2) and final (5) drying chambers.
The pre-drying chamber is a steel frame tunnel sheathed with duralumin shields. A chain conveyor runs along the tunnel, carrying bastuns with raw products. In this chamber, the moisture content of products is reduced by 5-6%, due to which they become more elastic, do not break off and do not stretch.
After pre-drying, the products enter the final drying chamber, which consists of a steel frame sheathed with duralumin shields, enclosed with heat-insulating gaskets. From the final drying chamber, the products are transferred by the same conveyor to the storage stabilizer for cooling.
Mesh-belt dryers are used for drying short-cut pasta. On fig. 2 shows a diagram of a dryer of this type, which refers to atmospheric dryers with air circulation heated directly in the drying chamber. There are four tapes with a total area of 80 m2 in the chamber. By means of a distribution-receiving device, raw products are loaded onto the upper belt, with the help of which they move along the upper zone of the dryer, then they are poured onto the second belt, from the second to the third, etc. From the last, fourth, belts in finished form, the products are transferred to the cooler - storage device.
The movement of the product is shown in the figure by arrows.
Each mesh tape is made of wire made of stainless steel, dimensions 20X200XX2000 mm and a free section of about 56%.
The tapes are stretched on two drums, one of which is a drive drum, the other is a tension one, and are supported by rollers. The drive for the belts is individual, equipped with a disk variator that allows you to change their speed from 0.14 to 1 m / min, i.e. more than 7 times.
There are four zones in the drying chamber - according to the number of tapes. Ribbed steam heaters are located in the space between the branches of the tapes.
The drying chamber operates under a vacuum created by an exhaust pipe, the base of which ends with an exhaust hood with a section of 10x2 m below, 3x2 m above and 3.4 m high. The height of the pipe is 10 m. exhaust air recirculation. From the workshop premises, air is sucked in through the ventilation windows of the lower zone, sequentially passes, starting from the bottom, all four zones, and before blowing the next layer of products, it is heated in heaters. From the upper zone, the air is thrown out through the exhaust hood and the pipe or partially returned through the outlet channel for recirculation to the first zone.
After reconstruction, the KSA-80 dryer serves three LPL-2M presses.
The loading of the upper belt is significant, but there is no danger of sticking and warping of the products, since the speed of the upper belt has been increased to 1600 mm/min and the air temperature in this zone is up to 58-60°C (instead of 45-55°C).
The second belt from the top is given a speed of 830 mm/min. The decrease in speed caused an almost twofold increase in the layer thickness, but such an increase is not dangerous for the second zone, since the products here are already dried up. The third tape moves even more slowly - at a speed of 770 mm / min; the product layer reaches its maximum thickness (60-70 mm). At the same time, the air temperature rises to 68°C. In this zone, drying mainly ends, the humidity of products is close to standard. In the fourth zone (belt speed 770 mm/min) the air temperature is maintained at 38-42°C.
The disadvantage of the KSA-80 dryer is the combination at its front front of loading raw and unloading finished products, which violates the linearity of the flow, making it a dead end.
The innovators of the Ufa pasta factory have changed the way the dryer is loaded. They began to load the first and second belts with raw products at the same time (from above). The direction of movement of the tapes, except for the first one from above, is reversed, due to which the production flow is leveled, the dead end is eliminated.
The speed of the first and second belts is 430 mm/min; the air temperature in both zones is 58-60°C. The loading of the tapes is carried out using a simple distribution comb installed across the entire width of the upper tape with an inclination of 45°. Getting on the teeth of the comb, the products partially fall into the gaps between them onto the first tape, and the rest slide off along the inclined plane onto the second tape.
Dried products from both belts are poured onto the third branch, which moves with some lead (450 mm/min). The air temperature in the third zone is 66-68°C.
The fourth tape has a speed of 380 mm/min, the air temperature in the zone is 56-68°C. On the reconstructed line, a hard drying regime has been introduced, applicable for noodles and vermicelli. Preliminary drying of products at the stage of cutting and their distribution in a thin layer on the first two belts makes it possible in the first period to achieve more or less uniform drying without warping of the product. At the Ufa pasta factory, horns are produced on this line.
