RU2803546C1 - Method of production of dry dairy products - Google Patents

Abstract

FIELD: food industry.

SUBSTANCE: invention relates to the food industry, namely to the production of dry dairy products of increased solubility. A method for the production of dry dairy products is proposed. Thermization of dairy raw materials is carried out at a temperature 63-68°C with aged from 15 to 30 seconds, cooled to a temperature of 4±2°C; then carry out the concentration of raw milk on film vacuum evaporation plant, where the raw milk is heated in a first series heaters to 46±2°C, 52±2°C, 57±2°C, 61±2°C; 65±2°C, respectively, and then sent to the plate heat exchanger, where it is heated to a temperature of 82±2°C and then to the pasteurizer where carry out heat treatment of raw materials at a temperature 76-97°C with an exposure of 5-7 seconds; then the flow from the pasteurizer is recirculated into a plate heat exchanger, in which the dairy raw materials are cooled to a temperature of 68±2°C, respectively, the raw materials coming from the last heater are heated; then the dairy raw materials are subjected to thickening in sequentially arranged four buildings of the evaporation plant. The dairy raw materials are first fed into the first body of the evaporation plant, where they are condensed at a pressure of 0.0685 MPa and a temperature of 68±2°C, then sent to the second body, where they are condensed at a pressure of 0.026 MPa and a temperature of 64±2°C, after which the dairy raw materials are sent to the fourth body, in which condensation is carried out at a pressure of 0.015 MPa and a temperature of 56±2°C, is then returned to the third body of the evaporation plant, in which condensation is carried out at a pressure of 0.020 MPa and a temperature of 60±2°C; from the third body, the condensed product is sent to a tubular heater, where it is heated to a temperature of 75±2°C, after which it is fed into the drying tower to the first stage of drying, which is carried out by spraying the condensed product in a hot air stream with a temperature of 170-190°C, and fed to the second stage, at which the particles are dried in a fluidized bed with hot air at a temperature of 80-110°C, after that, they are sent to dry and cool the dry product, which is carried out in a fluidized bed with air at first at a temperature of 45-60°C, then at a temperature of 8-10°C to a final humidity of 3-5% and to a dry product temperature no higher than 30°C. A fine fraction of dry product particles separated at the outlet of the drying tower is fed to the first stage of drying.

EFFECT: proposed method makes it possible to increase the solubility of milk powder with the preservation in the native state of the amount of whey proteins of milk more than 4 mg/g with a simultaneous increase in microbiological parameters.

9 cl, 1 dwg, 2 tbl, 3 ex

Description

The invention relates to the food industry, namely to a method for the production of dry dairy products of increased solubility.

Currently, many technologies for the production of dry dairy products are known. The most proven technology is based on preliminary condensation under vacuum and drying of milk raw materials in a stream of hot air (Lipatov N.N., Kharitonov V.D. Powdered milk: theory and practice of production. M.: Light and food industry st, 1981. 264 p.).

For thickening, circulation and film vacuum evaporation units are usually used. Circulating units are currently used mainly for the production of canned condensed milk with sugar, but before the widespread use of film vacuum evaporators in the dairy industry, circulating units were used in lines for the production of dry milk products. The thickening time in circulation units is slightly longer than the thickening time in film evaporators due to the nature of boiling, which occurs in circulating units in the volume of the product under the influence of hydrostatic depression and is therefore less efficient than in film evaporators, in which boiling occurs in a thin distribution over the surface heating tubes film.

The general structure and operating principle of vacuum evaporation units are approximately the same: a set of tubular heaters, a pasteurizer and housings, which are also tubular heat exchangers, for boiling and thickening the product due to evaporation. Usually, after heating in heaters, the raw materials are sent for heat treatment (pasteurization), which is carried out at fairly high temperatures from 95 to 107 ° C, to minimize the number of microorganisms and destroy lipolytic enzymes that could accumulate as a result of long-term storage of raw materials before drying during the development of psychrophilic microorganisms (developing at low temperatures). Also, at such high pasteurization temperatures, a large amount of whey proteins and other micronutrients in milk are destroyed.

After heat treatment, the raw material enters the thickening chamber, where, entering the vacuum zone, it instantly and intensively boils due to self-evaporation. In this case, there is an additional effect on the components of the milk, as well as the formation of foam. The foam can be partially carried away due to rarefaction, which leads to losses, as well as disruption of the boiling process due to incomplete coverage of the heating tubes and overheating of the thin film of foam, as a result of which even more proteins and trace elements are destroyed.

In the dairy industry, they mainly use two-, three-, four- and five-body plants, in which the vacuum and boiling point decrease from the first to the last body. The condensed raw material passes sequentially through all the housings and at the outlet has a temperature of 45-55°C. A decrease in temperature with a simultaneous increase in the concentration of dry substances leads to a significant increase in the viscosity of the thickened mixture, so the usually recommended concentration of dry substances in the mixture is 43-48%. The concentration of the mixture affects the particle size of the dry product - the higher the concentration of the mixture, the larger the size of the dried particles (Lipatov N.N., Kharitonov V.D. Powdered milk: theory and practice of production. M.: Light and food industry , 1981. 264 pp.; Vagn Vestergaard/ Technology for the production of milk powder. Evaporation and spray drying/ Vagn Vestergaard// Niro A/S, Copenhagen, Denmark, October 2003).

There is a known method of reducing the temperature of milk before entering the housing for condensation using a vacuum cooling chamber in SSP vacuum evaporation units. However, this method does not fundamentally solve the problem, since cooling also occurs due to self-evaporation, as a result of which sudden boiling and foaming occurs, and part of the foam also enters the housing along with the cooled raw material for thickening (Dytnersky Yu.I. Basic processes and apparatus of chemical technology: Design manual / G. S. Borisov, V. P. Brykov, Yu. I. Dytnersky, etc. Edited by Yu. I. Dytnersky, 2nd ed., revised and supplemented - M.: Chemistry, 1991. - 496 pp.).

The particle size of the dry product is usually in the range of 10-120 microns. It has been established that the solubility of dry milk products is significantly worsened by fractions up to 30 microns in size, and with an increase in particle sizes above 100 microns, the solubility improves proportionally (Lipatov N. N., Kharitonov V. D. Powdered milk: theory and practice of production. M. : Light and food industry, 1981. 264 p.). In this regard, there is increasing interest in instant agglomerated milk, the production process of which is not directly related to the drying process and is a separate process for processing the finished dry product in special installations. However, attempts are being made to provide larger particle sizes with increased solubility directly during the drying process.

The first method is to increase the mass fraction of dry substances in the thickened mixture before drying. The second is to ensure the agglomeration of particles during their drying and post-drying.

There is a known method used by the Vzduhotorg company, when small particles of the dry product are returned to a specially designed spray disk, where they are mixed with the condensed mixture (Equipment for drying milk and whey from the company "VZDUKHOTORG". Author: Mertin P., Kuznetsov P.V. Dairy Magazine industry", 2014, No. 3).

According to production experience, this method has a number of disadvantages and difficulties associated with washing spray discs and their operation.

The GEA company’s method is known, when during drying in a fluidized bed the dry product is moistened with prepared cooking steam, due to which its ability to agglomerate improves, and the particles stick together and increase in size (Vagn Vestergaard / Technology for the production of milk powder. Evaporation and spray drying / Vagn Vestergaard/Niro A/S, Copenhagen, Denmark, October 2003).

This method has a number of disadvantages associated with the need to prepare high-quality steam that does not contain impurities, as well as with the instability of the process, which may result in the formation of large and overly moistened lumps of the product, which leads to both product losses and the formation of sticky lumps with worse solubility.

The closest analogue to the patented solution is a method for producing powdered milk, which consists of preliminary standardization of milk, heat treatment, evaporation, spray drying and fluidized bed drying in order to increase the solubility of the dry powder (RF patent No. 2267274, published 01/10/2006).

This production method refers to the production of only fat-containing types of dry milk products (whole milk powder and milk mixtures containing non-dairy fat) and solves the problem of homogenization of highly viscous condensed mixtures. This production method does not solve the problem of preserving the components of milk as a result of long-term temperature exposure and secondary microbiological contamination during the production process.

Also, the disadvantages of the known method are unstable and low microbiological indicators of the finished product, low solubility, increased losses of dry substances, especially biologically active and valuable components of milk, as well as increased energy consumption in production.

For dry dairy products used as raw materials in the food industry, mainly for the production of baby food, the confectionery industry, obtained by dry mixing of components and intended for direct human consumption without preliminary heat treatment, of all others, two groups of indicators are important , the improvement of which by changing the technological modes of processes, their sequence or technical solutions of technological equipment and production lines is in conflict.

The first group of indicators are indicators of the solubility of a dry milk product, the first indirect characteristic of which is the preservation in the native state (natural, not denatured, not changed relative to the original) of as much whey milk proteins as possible. Whey proteins of milk have low thermal stability and when milk is heated, some of its fractions begin to denature and precipitate at 62 °C. The residual content of whey proteins is determined by the polarimetric method and is expressed by the whey protein nitrogen index (WPNI, whey protein nitrogen index) in milligrams of whey protein nitrogen in a clarified solution of a product sample weighing 1 gram. For a dry milk product with high solubility, this figure should exceed 4 mg/g, which can mainly be achieved by reducing the temperature of the mandatory heat treatment of raw materials (pasteurization).

The second characteristic of solubility is the particle size of the dry product, which usually (with known drying technologies) is in the range from 10 to 120 microns. According to theoretical and practical data, excluding the fine fraction of particles up to 30 microns and increasing the particle size of the dry product to the range from 30 to 240 microns significantly improves solubility (Lipatov N. N., Kharitonov V. D. Powdered milk: theory and practice of production M.: Light and food industry, 1981. 264 p.).

The second group of indicators are microbiological indicators, which mainly include the number of colony forming units (CFU) of anaerobic and facultative anaerobic microorganisms (CMAFAnM) in 1 gram of dry product and the absence of coliform bacteria (coliforms) in a certain amount.

Regarding the first group of indicators, microbiological indicators can be improved by a set of measures, including increasing heat treatment temperatures, which is the contradiction between the first and second groups of indicators.

The technical problem solved by the proposed invention is to eliminate the shortcomings of known methods, as well as to obtain dry dairy products with high characteristics of both solubility (WPNI index and linear particle size) and microbiological indicators (QMAFAnM and coliforms).

The technical result when using the proposed production method is expressed in increasing the solubility of the dry milk product (WPNI index and linear particle size) with preservation in the native state of the amount of whey proteins of milk more than 4 mg/g with a simultaneous increase in microbiological indicators (QMAFAnM and coliforms), improvement of the described indicators relative to those standardized in the current regulatory and technical documentation or relative to the empirical data given in sources, and is presented in Table 1.

Table 1

No. Index Empirical values or NTD indicators Indicator values as a result of using the proposed production method 1 Whey protein nitrogen index (WPNI, whey protein nitrogen index), mg/g 1.4 – 7 Guaranteed to provide
>4 2 Linear particle size, microns 10 - 120 30 - 240 3 KMAFAnM, CFU/g, no more 1*10 ⁴ 1*10 ³ 4 coliforms, absent in g of product 0.1 1

The specified technical result is achieved by implementing a method for the production of dry dairy products, which consists in the following:

pre-prepared (purified, standardized and homogenized) dairy raw materials are subjected to thermization at a temperature of 63-68 ° C with a holding time of 15 to 30 seconds, cooled to a temperature of (4 ± 2) ° C;

the milk raw materials are thickened in a film vacuum evaporation unit, in which the milk raw materials are first sequentially heated in heaters to 46±2°C, 52±2°C; 57±2°С; 61±2°С; 65±2°C, respectively, after which it is sent to a plate heat recuperator, where it is heated to a temperature of 82±2°C and then to a pasteurizer, where the raw materials are heat treated at a temperature of 76-97°C with a holding time of 5-7 seconds, flow from the pasteurizer they are recirculated into a plate recuperator, in which the milk raw materials are cooled to a temperature of 68±2°C and, accordingly, the raw materials coming from the last heater are heated;

Next, the milk raw materials are subjected to condensation in four sequentially located housings of the evaporation unit, while the milk raw materials are first fed into the first housing of the evaporation unit, in which condensation is carried out at a pressure of 0.0685 MPa and a temperature of 68±2°C, then sent to the second housing, to in which thickening is carried out at a pressure of 0.026 MPa and a temperature of 64±2°C, after which the milk raw materials are sent to the fourth housing, in which thickening is carried out at a pressure of 0.015 MPa and a temperature of 56±2°C, then returned to the third housing of the evaporation unit, in which thickening is carried out at a pressure of 0.020 MPa and a temperature of 60±2°C;

from the third body, the condensed product is sent to a tubular heater, where it is heated to a temperature of 75±2°C, after which it is fed into the drying tower for the first stage of drying, which is carried out by spraying the condensed product in a stream of hot air with a temperature of 170-190°C and fed to the second stage, at which the particles are dried in a fluidized bed with hot air at a temperature of 80-110°C, after which they are sent for drying and cooling of the dry product, which is carried out with air, first at a temperature of 45-60°C, then at a temperature of 8 -10°C to a final humidity of 3-5% and to a temperature of the dry product not higher than 30°C, while the fine fraction of dry product particles separated at the outlet of the drying tower is fed to the first stage of drying.

In the proposed method, raw milk passes through five heaters, where it is sequentially heated and then sent to a pasteurizer for heat treatment, which is preferably carried out at a temperature of (95±2) °C for whole milk, (84±2) °C for skim milk and (78±2) °C for whey with a holding time of 5-7 seconds. This treatment ensures the lowest degree of denaturation of whey proteins and high microbiological parameters.

Before entering the pasteurizer, raw milk passes through a plate heat recuperator, where it is heated by raw materials that have already undergone heat treatment. Thus, heat recovery is carried out - heating of raw milk before heat treatment due to the heat of the raw material after heat treatment. Thanks to recovery, milk raw materials are supplied for condensation at a given temperature, as a result of which there is no sudden boiling due to self-evaporation and the formation of foam, since sudden boiling and the presence of foam worsen boiling conditions and lead to excessive denaturation of whey proteins and the loss of other micronutrients.

Thus, the use of a plate recuperator in the vacuum evaporation installation for the proposed production method allows not only to save energy for heat treatment, but also to provide optimal temperature and conditions for the start of boiling, thereby achieving maximum preservation of the components of raw milk materials, in particular whey proteins milk.

Condensation of milk raw materials in a film vacuum evaporation unit, the time of thermal exposure of whey proteins in which is less than when condensing in a circulation unit, ensures the greatest preservation of whey proteins.

A feature of the proposed method is that the milk raw materials pass through the buildings not in order, but in the sequence 1, 2, 4 and 3 buildings. Thus, entering from the second body into the fourth, the condensed product first cools to a temperature of (56±2) °C, corresponding to the boiling point at a vacuum of 0.015 MPa, and entering after the fourth body into the third, the product is first heated before boiling and condensation begins, and the temperature at the outlet of the vacuum evaporation unit after the end of thickening is (60±2) °C.

This temperature is higher than with known production methods, when the condensed product leaves the fourth housing at temperatures of the order of (56 ± 2) ° C, which makes it possible to condense milk raw materials to a higher concentration of dry substances, since a mixture with a higher temperature has a higher fluidity due to reduced viscosity. Condensation of whole milk in the proposed production method is carried out to a concentration of dry substances (52±2)%, skim milk - (50±2)%, whey (55±2)%, which is higher than for known production methods. A higher content of dry substances in the condensed product makes it possible to obtain larger particles of the dry product during the drying process, since the mass content of dry substances in a “drying” drop of equal volume is greater.

The increased temperature of the condensed mixture also makes it possible to prevent the development of thermophilic microflora during intermediate storage of the mixture before drying, which also ensures high microbiological characteristics of the finished product. At the same time, the temperature of the condensed mixture does not exceed the lower limit for the beginning of whey protein coagulation of 62 ° C, therefore, there is practically no decrease in the content of whey proteins during storage.

Heating the condensed product before drying to a temperature of (75±2)°C can be considered an additional heat treatment, which prevents an increase in the content of microorganisms that could arise due to secondary contamination from the surfaces of the equipment after heat treatment in the pasteurizer - the housings of the vacuum evaporation unit, tanks and pipelines, or during short-term storage of the mixture before drying.

Also, heating the condensed product reduces its viscosity, which improves spray conditions using a spray device, especially if nozzles are used as a spray device.

In addition, heating the condensed product before the first stage of drying in a tubular heat exchanger with hot water or evacuated steam provides optimal heating conditions, which saves energy and time for heating the condensed mixture in the tower with hot air, since heat transfer from hot air is up to 10 times worse, than from the wall surface of the heating tubes, and begin the drying process almost immediately after the mixture enters the tower. This contributes to both the most uniform drying of sprayed droplets of the condensed mixture, and better technical and economic indicators of the process - higher efficiency of heat input, and higher productivity of the drying unit.

After heating to the optimal drying temperature, the condensed mixture enters the first stage of drying - spray drying in a drying tower with hot air, which is supplied tangentially to the upper part of the drying tower to create a rotating flow of the drying medium.

The air temperature is selected depending on the required performance of the drying unit, the type of finished product and the moisture content in it. For whole and skim milk, a higher temperature (180-190) °C is most often selected, and for whey, a lower temperature (170-180) °C is selected for drying under milder conditions due to the thermoplastic property of acidic curd whey.

In particular, the condensed product is sprayed in the form of small drops in a stream of hot air using a rotary sprayer with a spray disk rotating at a frequency of 8000-10000 rpm, or using nozzle sprayers equipped with high-pressure pumps.

In the proposed production method, a small fraction of dry product particles, collected at the outlet of the drying tower by means of cyclones, which can operate in conjunction with fine filters, is supplied through air ducts to the first stage of drying into the zone of spraying of the condensed mixture, where adhesion occurs with the sprayed under-dried drops of the condensed mixture. product due to which agglomeration of particles occurs. In this case, no additional equipment or complication of the sprayer design is required. Air ducts are easily cleaned during standard cleaning procedures.

Thus, due to the increased mass fraction of dry substances in the condensed product and the return of the fine fraction of the dry product to agglomeration in the drying zone of the first drying stage, the dry product is freed from the content of the fine fraction of dry particles up to 30 microns and the particle size of the dry product is increased up to 240 microns .

Since the dry particles of the product at the first stage of drying do not reach the final required mass fraction of moisture, which at this stage is (6-8)%, they are sent for further drying in a fluidized (“boiling”) bed to the lower conical part of the drying tower, which has perforated bottom (integrated fluid bottom) onto which product particles settle. Hot air is supplied through the perforations in the bottom of the drying tower and aerates the layer of product particles, due to which they continue to dry. Direct physical contact of particles in the “fluidized” bed and the presence of residual moisture leads to partial agglomeration of particles at this stage of drying. Lighter particles of the dry product that have reached a humidity of (4-6)% are transferred by the air flow to the airlock, through which they leave the drying tower and enter the next stage of drying.

The third stage of drying, the so-called post-drying, and cooling of the dry product are carried out in a vibro-fluid dryer (“trough”), which is a longitudinal hollow apparatus with a perforated bottom, consisting of two sections, mounted on spring supports and equipped with vibration motors. Through the perforations in the bottom of the first section, warm air with a temperature of (45-60) °C is supplied to dry the particles to the final humidity (3-5)%, through the perforations of the second section, cold air with a temperature of (8-10) °C is supplied to cool the finished dry product. to a temperature not exceeding 30 °C.

The exact values of the air temperature at the second and third stages of cooling are determined based on the required final humidity of the finished product, the current performance of the drying unit, the time of year and the moisture content of the atmospheric air.

As dairy raw materials, it is possible to use, in particular, whole milk, skim milk, cheese or curd whey.

Before condensation, preliminary preparation of milk raw materials is carried out, which must be carried out within no more than 36 hours from the moment the milk is received and cooled to (4±2) °C. Whey obtained during the production of cheese and cottage cheese must be subjected to preliminary preparation immediately.

During preliminary preparation, whole milk is subjected to purification, normalization for fat and protein (standardization) and homogenization; skim milk is obtained by separating whole milk from cream; whey is subject to filtration and separation in order to separate protein and fat particles, and can also be subjected to pre-concentration in membrane units. These operations can be performed on any technological equipment and production lines available to the manufacturer.

Next, the prepared milk raw materials are subjected to thermization. Thermization is the heat treatment of milk at a temperature of (63-68) °C with a holding time of 15 to 30 seconds. This treatment can significantly reduce the number of microorganisms with minimal destruction of milk components, mainly whey proteins, vitamins and other micronutrients. Thermization inactivates mainly psychrophilic microorganisms that can develop in milk at low temperatures, so milk raw materials subjected to thermization can be stored without a noticeable change in acidity and heat stability at temperatures below 8 ° C for up to three days, and at a temperature of (0-1) ° C - until seven. For this reason, thermization is especially important in the production of dry dairy products, since due to large volumes of processing and relatively low production lines, the storage time of raw materials can reach several days.

Thermization of dairy raw materials is carried out on plate installations consisting of heating and cooling sections in such a way that after heating to the thermization temperature, the raw materials are cooled to the storage temperature (4±2) °C. Plate installations can be equipped with separators-cleaners, cream separators and normalizers, as well as homogenizers, so the thermization operation can be carried out in one cycle with the processes for preparing milk raw materials, depending on the technological equipment and production lines that are available to the manufacturer.

Next, prepared, thermalized and cooled to a temperature of (4±2) °C, raw milk is sent to storage tanks before and during the technological process. The storage time of raw materials until the end of processing should be no more than two days, the temperature should not exceed 6 °C.

In particular, after thickening, the product is sent to tanks for storage before drying, which is usually short-term. It is believed that at temperatures of 45-55°C the development of thermophilic microorganisms is already possible; in fact, it has been established that after 14-16 hours of continuous process, the total content of microbial cells in dry milk products begins to increase. Thus, the increased temperature of the condensed product in the proposed production method helps prevent the development of microorganisms and prevent an increase in their number in the finished product.

In particular, the film vacuum evaporation unit includes five tubular heaters, a plate heat recuperator, a tubular pasteurizer and four evaporation unit housings.

Dairy raw materials to be dried, before being sent to storage tanks before and during the technological process, are supplied to the equipment of the receiving department, hardware and production shops, where they undergo preliminary preparation, which must be carried out within no more than 36 hours from the date of receipt and cooling the milk to (4±2) °C. Whey obtained during the production of cheese and cottage cheese must be subjected to preliminary preparation immediately.

The technological process of processing raw milk into dry milk products fundamentally consists of two main stages - thickening the milk raw materials and drying the thickened mixture to obtain a dry powder with a specified mass fraction of residual moisture.

Condensation of milk raw materials is carried out in vacuum evaporation units.

Vacuum evaporation units consist of heaters, a pasteurizer (heater for temperature treatment) and housings designed directly for thickening milk raw materials as a result of boiling and evaporation of moisture.

Depending on the design of the housings and the characteristics of the boiling process, circulation and film vacuum evaporation plants are distinguished. The boiling process in film vacuum evaporation units is characterized by a higher intensity at the same temperatures as in circulation ones, and therefore a shorter duration of the process. The condensation time in circulating vacuum evaporation units is about 40 minutes, and in film evaporators it does not exceed 15 minutes.

The proposed production method involves thickening milk raw materials in a film vacuum evaporation unit, the time of thermal exposure of whey proteins in which is less than when thickening in a circulation unit, which ensures the greatest preservation of whey proteins.

Thickening is carried out on a film vacuum evaporation unit, consisting of five tubular heaters, a plate heat recuperator, a tubular pasteurizer and four buildings for thickening milk raw materials.

Raw milk passes through five heaters, where it is sequentially heated to (46±2) °C; (52±2) °С; (57±2) °С; (61±2) °С; (65±2) °C and then sent to the pasteurizer for heat treatment.

The proposed production method involves heat treatment at a temperature of (95±2) °C for whole milk, (84±2) °C for skim milk and (78±2) °C for whey for 5-7 seconds, which in total with thermization, cooling and storage of dairy raw materials before processing under the specified conditions ensures the lowest degree of denaturation of whey proteins and high microbiological indicators .

Before entering the pasteurizer, raw milk passes through a plate heat recuperator, where it is heated to a temperature of (82±2) °C by raw materials that have already undergone heat treatment. Heat exchange occurs through the surface of the heat exchange plates and, due to the design of the recuperator, mixing of the flows of raw materials that have undergone heat treatment and those that have not undergone heat treatment does not occur. Thus, heat recovery is carried out - heating of raw milk before heat treatment due to the heat of the raw material after heat treatment.

Dairy raw materials that have undergone heat treatment in a pasteurizer at a temperature of 76-97 ° C with a holding time of 5-7 seconds are cooled in the recuperator to a temperature of (68 ± 2) ° C and sent to the first housing to begin its thickening. Thickening is carried out to a mass fraction of dry substances (12±2)% due to boiling and evaporation of moisture under reduced pressure (vacuum). The pressure in the first housing is 0.0685 MPa, which corresponds to the boiling point (68±2) °C, so the milk raw material, thanks to recovery, is supplied to condensation at a given temperature, as a result of which there is no sudden boiling due to self-evaporation and the formation of foam. Rapid boiling and the presence of foam worsens boiling conditions and leads to excessive denaturation of whey proteins and loss of other micronutrients.

Thus, the use of a plate recuperator in the vacuum evaporation installation for the proposed production method allows not only to save energy for heat treatment, but also to provide optimal temperature and conditions for the start of boiling, thereby achieving maximum preservation of the components of raw milk materials, in particular whey proteins milk.

Next, the milk raw material is subjected to condensation in the second, fourth and third buildings under the following conditions: 2 case - pressure 0.026 MPa, temperature (64±2) °C; 4 body - 0.015 MPa, (56±2) °C; 3 body - 0.020 MPa, (60±2) °C. Condensation is carried out to a mass fraction of dry substances of (21±2)% in the second body, (29±2)% in the fourth, (52±2)% for whole milk, (50±2)% for skim milk and (55±2 ) % for whey in the third.

After thickening until the required concentration is reached, the thickened mixture is sent to a tank for short-term storage before drying. In fact, there is no storage of the mixture, since the tank acts as a balancing tank to maintain a small supply of the thickened mixture before drying. Thus, after thickening, the mixture enters the tank, from where it is continuously supplied for heating and drying by a positive displacement pump.

Drying is carried out in a drying installation, consisting of a drying tower with an integrated fluid bottom, an external vibration-fluid dryer (“trough”), a set of equipment for heating, cooling and pumping process air, extracting “exhaust” air, as well as a set for cleaning exhaust air from small particles of dry product - cyclones and fine filters.

Drying the condensed mixture consists of three stages, followed by cooling of the dry product. The proposed production method before the first stage of drying includes the operation of heating the mixture to the optimal temperature in the drying zone of the drying tower (75±2) °C on a tubular heat exchanger with hot water or evacuated steam, which provide optimal heating conditions. This allows you to save energy and time for heating the condensed mixture in the tower with hot air, since heat transfer from hot air is up to 10 times worse than from the wall surface of the heating tubes, and to begin the drying process almost immediately after the mixture enters the tower. This contributes to both the most uniform drying of sprayed droplets of the condensed mixture, and better technical and economic indicators of the process - higher efficiency of heat input, and higher productivity of the drying unit.

Heating the condensed mixture before drying can be considered an additional heat treatment, which prevents an increase in the content of microorganisms that could arise due to secondary contamination from the surfaces of equipment after heat treatment in a pasteurizer - vacuum evaporator housings, tanks and pipelines, or during short-term storage mixtures before drying.

Also, heating the thickened mixture reduces its viscosity, which improves the conditions for its spraying using a spray device, especially if nozzles are used as a spray device.

After heating to the optimal drying temperature, the condensed mixture enters the first stage of drying - spray drying in a drying tower with hot air at a temperature of (170-190) °C. The air temperature is selected depending on the required performance of the drying unit, the type of finished product and the moisture content in it. For whole and skim milk, a higher temperature (180-190) °C is most often selected, and for whey, a lower temperature (170-180) °C is selected for drying under milder conditions due to the thermoplastic property of acidic curd whey.

Hot air is supplied tangentially to the upper cylindrical part of the drying tower to create a rotating flow of the drying medium. The condensed mixture is sprayed in the form of small drops in a stream of hot air using a rotary sprayer with a special spraying device - a spray disk rotating at a frequency of 8000-10000 rpm. Once in the flow of a hot medium, moisture begins to evaporate from the surface of the droplets and the particles dry out. Due to the heat consumption for evaporation, the air temperature in the drying zone drops sharply and at the exit from the drying tower is (80-90) °C, while the temperature of the dry product does not exceed (75±2) °C.

To spray the condensed mixture, you can also use nozzle sprayers equipped with high-pressure pumps; heating the condensed mixture improves the spraying conditions using nozzles, however, in the case of whey powder production, especially if an additional operation of lactose crystallization is carried out, the nozzles can often become clogged during operation.

The higher the content of dry substances in the condensed mixture, the larger the particles of the dry product formed after drying. In addition, in the proposed production method, at the first stage of drying, a fine fraction of dry product particles, separated by cyclones from the “exhaust” air after leaving the dryer, is supplied to the spray zone of the condensed mixture through air ducts. To increase the efficiency of fine fraction separation, fine air filters are often used in combination with cyclones. Here, directly at the level of the spray disk, the air ducts open and small particles stick together with the still undried drops of the sprayed condensed mixture, that is, their enlargement occurs - agglomeration.

Thus, due to the increased mass fraction of dry substances in the condensed mixture and the return of the fine fraction of the dry product to agglomeration in the drying zone of the first drying stage, the dry product is freed from the content of the fine fraction of dry particles up to 30 microns and the particle size of the dry product is increased to 30-240 µm.

Dry particles of the product at the first stage of drying do not reach the final required mass fraction of moisture, which at this stage is (6-8)%. The lower conical part of the drying tower is a so-called fluidized or "fluidized" bed dryer, and has a perforated bottom (integrated fluid bottom) onto which product particles settle. Through the perforations in the bottom of the drying tower, made towards the exit from the dryer, hot air with a temperature of (80-110) °C is supplied and aerates the layer of product particles, due to which they continue to dry, twisting and moving in suspension in the air flow. Direct physical contact of particles in the “fluidized” bed and the presence of residual moisture leads to partial agglomeration of particles at this stage of drying. Lighter particles of the dry product that have reached a humidity of (4-6)% are gradually transferred by the air flow to the airlock at the outlet of the dryer, through which they leave the drying tower and enter the next stage of drying.

The third stage of drying, the so-called post-drying, and cooling of the dry product are carried out in a vibro-fluid dryer (“trough”), which is a longitudinal hollow apparatus with a perforated bottom, consisting of two sections, mounted on spring supports and equipped with vibration motors. Through the perforations in the bottom of the first section, warm air with a temperature of (45-60) °C is supplied to dry the particles to the final humidity (3-5)%, through the perforations of the second section, cold air with a temperature of (8-10) °C is supplied to cool the finished dry product. to a temperature not exceeding 30 °C.

The exact values of the air temperature at the second and third stages of cooling are determined based on the required final humidity of the finished product, the current performance of the drying unit, the time of year and the moisture content of the atmospheric air.

The cooled dry product is sent for intermediate storage or directly for packaging using pneumatic transport with cold air (8-10) °C, where it is finally cooled to a temperature not exceeding 20 °C. If the required temperature of the product is not reached, then until it is shipped to the consumer, the packaged product is cooled in the refrigeration chamber.

Before being fed to the dosing device of the packaging line, the finished product is sieved using a vibrating sieve with a 2x2 mm mesh to separate large lumps of product.

The finished product is stored at a temperature not exceeding 20 °C and a relative air humidity not exceeding 85%. The shelf life of products is set by the manufacturer.

The following are examples of the production of dry milk products according to the proposed method.

Example 1.

After quality assessment and acceptance, whole cow's milk is sent to a pasteurization-cooling unit equipped with a separator-normalizer, where whole milk is standardized by fat content and the standardized whole milk is thermized at a temperature of (66±2) °C with a holding time of 20 seconds, after which the milk cooled and sent for storage before thickening and drying begins.

When fed into a four-body film vacuum evaporation unit, standardized whole milk is sequentially heated in five heaters and a plate recuperator to I - (46±2) °C; II - (52±2) °С; III - (57±2) °С; IV - (61±2) °C; V - (65±2) °C and (82±2) °C in the recuperator, respectively, and enters the pasteurizer, where it undergoes heat treatment at a temperature of (95±2) °C without holding.

Next, whole milk enters sequentially into the first, second, fourth and then third buildings for evaporation, where it boils at a vacuum and temperatures I - 0.0685 MPa, (68 ± 2) ° C; II - 0.026 MPa, (64±2) °C; IV - 0.015 MPa, (56±2) °C and III - 0.020 MPa, (60±2) °C, respectively, after which it reaches the required concentration of milk solids (52±2)%, and with temperature (60±2) °C is sent for short-term storage before drying.

Condensed whole milk is then heated to (75±2) °C and sprayed into the drying tower with a disk centrifugal sprayer in a stream of hot air at a temperature of (182±2) °C for drying. Drying and cooling of whole milk powder is carried out under gentle conditions in the form of a fluidized layer with air at temperatures of (105±2) °C, (55±2) °C and (8-10) °C. The fine fraction of the dry product, separated from the exhaust air in the air purification system, is returned by pneumatic transport to the spray zone for agglomeration.

Whole milk powder with a temperature of (26±2) °C and a humidity of (3.6±0.2)% is sent for intermediate storage, packaging and additional cooling in a chamber to a temperature not higher than (18±2) °C.

Example 2.

Curd whey from the cottage cheese production site is sent to intermediate storage and then supplied to a pasteurization and cooling unit equipped with a separator-cleaner and a cream separator, where it is freed from protein dust and milk fat. The whey is then thermalized at a temperature of (65±2) °C for 20 seconds, after which it is cooled and sent for storage until condensation and drying begin.

When fed into a four-body film vacuum evaporation unit, the whey is sequentially heated in five heaters and a plate recuperator to I - (46±2) °C; II - (52±2) °С; III - (57±2) °С; IV - (61±2) °C; V - (65±2) °C and (82±2) °C in the recuperator, respectively, and enters the pasteurizer, where it undergoes heat treatment at a temperature of (78±2) °C without holding.

Next, the whey enters sequentially into the first, second, fourth and then third buildings for evaporation, where it boils at a vacuum and temperatures I - 0.0685 MPa, (68±2) °C; II - 0.026 MPa, (64±2) °C; IV - 0.015 MPa, (56±2) °C and III - 0.020 MPa, (60±2) °C, respectively, after which it reaches the required concentration of milk solids (55±2)%, and with temperature (60±2) °C is sent for short-term storage before drying.

The condensed whey is then heated to (75±2) °C and sprayed into the drying tower with a disk centrifugal sprayer in a stream of hot air at a temperature of (175±2) °C for drying. Dry whey is dried and cooled under gentle conditions in the form of a fluidized layer with air at temperatures of (85±2) °C, (55±2) °C and (8-10) °C. The fine fraction of the dry product, separated from the exhaust air in the air purification system, is returned by pneumatic transport to the spray zone for agglomeration.

Dry whey with a temperature of (26±2) °C and a humidity of (3.2±0.2)% is sent for intermediate storage, packaging and further cooling in a chamber to a temperature not higher than (18±2) °C.

Example 3.

After quality assessment and acceptance, whole cow's milk is sent to a pasteurization and cooling unit equipped with a cream separator, where whole milk is separated into skim milk and cream, after which the skim milk is thermized at a temperature of (66±2) °C with a holding time of 20 seconds , after which it is cooled and sent for storage until thickening and drying begins.

When fed into a four-body film vacuum evaporation unit, skim milk is sequentially heated in five heaters and a plate recuperator to I - (46±2) °C; II - (52±2) °С; III - (57±2) °С; IV - (61±2) °C; V - (65±2) °C and (82±2) °C in the recuperator, respectively, and enters the pasteurizer, where it undergoes heat treatment at a temperature of (84±2) °C without holding.

Next, the skim milk enters sequentially into the first, second, fourth and then third buildings for evaporation, where it boils at a vacuum and temperatures I - 0.0685 MPa, (68±2) °C; II - 0.026 MPa, (64±2) °C; IV - 0.015 MPa, (56±2) °C and III - 0.020 MPa, (60±2) °C, respectively, after which it reaches the required concentration of milk solids (50±2)%, and with temperature (60±2) °C is sent for short-term storage before drying.

The condensed skim milk is then heated to (75±2) °C and sprayed into the drying tower by a disk centrifugal sprayer in a stream of hot air at a temperature of (188±2) °C for drying. Drying and cooling of skim milk powder is carried out under gentle conditions in the form of a fluidized layer with air at temperatures of (95±2) °C, (50±2) °C and (8-10) °C. The fine fraction of the dry product, separated from the exhaust air in the air purification system, is returned by pneumatic transport to the spray zone for agglomeration.

Powdered skim milk with a temperature of (26±2) °C and a humidity of (4.8±0.2)% is sent for intermediate storage, packaging and additional cooling in a chamber to a temperature not higher than (18±2) °C.

Example 4 and 5.

The production of skimmed milk powder was carried out using technology corresponding to Example 3 on other days and using raw materials obtained from other farms of different quality.

The characteristics of the obtained products, confirming the achievement of the technical result, are given in Table 2.

table 2

No. Product Whey protein nitrogen index (WPNI, whey protein nitrogen index), mg/g Linear particle size, microns KMAFAnM, CFU/g, no more coliforms, absent in g of product Value confirming the technical result >4 30 - 240 1*10 ³ 1 1 Whole milk powder -* 42 - 210 5*10 ² 1 2 Whey powder -* 30 - 184 7*10 ² 1 3 Skimmed milk powder 5.5 44 - 194 2*10 ² 1 4 Skimmed milk powder 4.7 40 - 205 8*10 ² 1 5 Skimmed milk powder 5.2 36 - 214 3*10 ² 1

*Whey Protein Nitrogen Index (WPNI) is not determined in whole milk powder and whey powder.

Next, the physicochemical and microbiological parameters of the resulting products were assessed.

The content of undenatured whey proteins in COM, characterized by the WPNI index, was carried out by spectrophotometry using a Uvi Light XS5 photometer. According to the analysis procedure, two parallel measurements of the light transmission of the clarified solution after casein precipitation were performed, the convergence of which should be at least 2%. The average transmittance between parallel measurements was used to obtain the WPNI value from the calibration curve (Fig. 1).

The particle size of dry products was determined by microscopying the preparation on a Celestron Advanced 500x monocular optical microscope equipped with an eyepiece micrometer.

The number of mesophilic aerobic and facultative anaerobic microorganisms (KMAFAnM) was determined according to GOST 10444.15; determination of the content of coliform bacteria (coliform bacteria) - according to GOST 31747.

Claims (13)

1. A method for producing dry dairy products, which consists in the fact that pre-prepared dairy raw materials are subjected to thermization at a temperature of (63-68) ° C with a holding time of 15 to 30 seconds, cooled to a temperature of (4 ± 2) ° C; the milk raw materials are thickened in a film vacuum evaporation unit, in which the milk raw materials are first sequentially heated in heaters to 46±2°C, 52±2°C, 57±2°C, 61±2°C; 65±2°C, respectively, after which it is sent to a plate heat recuperator, where it is heated to a temperature of 82±2°C, and then to a pasteurizer, where the raw materials are heat treated in a plate recuperator, in which the milk raw materials are cooled to a temperature of 68±2 °C and, accordingly, heating of the raw materials coming from the last heater; Next, the milk raw materials are subjected to condensation in four sequentially located housings of the evaporation unit, while the milk raw materials are first fed into the first housing of the evaporation unit, in which condensation is carried out at a pressure of 0.0685 MPa and a temperature of 68±2°C, then sent to the second housing, to in which thickening is carried out at a pressure of 0.026 MPa and a temperature of 64±2°C, after which the milk raw materials are sent to the fourth housing, in which thickening is carried out at a pressure of 0.015 MPa and a temperature of 56±2°C, then returned to the third housing of the evaporation unit, in which thickening is carried out at a pressure of 0.020 MPa and a temperature of 60±2°C; from the third body, the condensed product is sent to a tubular heater, where it is heated to a temperature of 75±2°C, after which it is fed into the drying tower for the first stage of drying, which is carried out by spraying the condensed product in a stream of hot air with a temperature of 170-190°C and fed to the second stage, at which the particles are dried in a fluidized bed with hot air at a temperature of 80-110°C, after which they are sent for drying and cooling of the dry product, which is carried out in a fluidized bed with air, first at a temperature of 45-60°C, then - with a temperature of 8-10°C to a final humidity of 3-5% and to a temperature of the dry product not higher than 30°C, while the small fraction of dry product particles separated at the outlet of the drying tower is fed to the first stage of drying. 2. The method for producing dry dairy products according to claim 1, which consists in using whole milk, skim milk, cheese or curd whey as dairy raw materials. 3. The method for producing dry dairy products according to claim 1, which consists in the fact that after thickening the product is sent to storage tanks before drying. 4. The method for producing dry dairy products according to claim 1, which consists in the fact that heat treatment in tubular heaters is carried out at a temperature of (95±2)°C for whole milk, (84±2)°C for skim milk and (78± 2)°C for whey without aging . 5. The method for producing dry dairy products according to claim 1, which consists in the fact that after condensation, the condensed mixture is sent to a tank for short-term storage before drying. 6. The method for producing dry dairy products according to claim 1, which consists in heating the condensed product before the first stage of drying in a tubular heat exchanger with hot water or evacuated steam. 7. The method for producing dry dairy products according to claim 1, which consists in the fact that hot air at the first stage of drying is supplied to the upper part of the drying tower tangentially to create a rotating flow of the drying medium. 8. A method for producing dry dairy products according to claim 1, which consists in the fact that the condensed mixture is sprayed in the form of small drops in a stream of hot air using a rotary sprayer with a spray disk rotating at a frequency of 8000-10000 rpm, or using nozzles sprayers equipped with high pressure pumps. 9. The method for producing dry dairy products according to claim 1, which consists in the fact that the cooled dry product is sent for intermediate storage or packaging using pneumatic transport with cold air at a temperature of 8-10 ° C, where it is finally cooled to a temperature not exceeding 20 °C.