Description of the design and operation of the homogenizer. Homogenizers Homogenizer in line

Dairy products play an important role in the nutrition of people, especially children, the elderly and the sick. The dietary properties of fermented milk products are, first of all, that they improve metabolism, stimulate the secretion of gastric juice and stimulate appetite. The presence in their composition of microorganisms that can take root in the intestines and suppress the putrefactive microflora leads to inhibition of putrefactive processes and the cessation of the formation of toxic protein breakdown products that enter the human blood.

An important stage in the production of fermented milk products is the mechanical impact on the feedstock, i.e. homogenization. It not only prevents the settling of fat, but also contributes to the production of high-quality fermented milk products with improved texture and taste, increase its digestibility by the body and more complete use of the fat and vitamins contained in it.

Raw milk goes through several stages of preparation before entering the conditional conveyor of the food industry. At the moment, there are several groups of chemical, thermal and biological processing operations. Milk homogenization occupies a special place in the overall complex of raw product preparation. This is a mechanical processing technology, but depending on the specific technique, it may also include separate procedures for thermal and chemical exposure.

General information about homogenization

In principle, this technology is used as a method of mechanical processing of dairy and other liquid products in order to increase the dispersion of their fat phase. In the course of the technological process, the heterogeneity of the distribution of chemical elements throughout the entire volume of the heterophase system also decreases. At the same time, this technique should not be confused with dispersion as such. According to the definition of milk homogenization, the crushing of the dispersed phase is not a prerequisite for the technological process. For example, the procedure for mixing solid powders may well exclude this operation. Conversely, dispersion of a heterophasic system may involve and also exclude a homogenization procedure.

Purpose of technology

The goals of homogenization may vary depending on the current state of the raw milk and the requirements for the final product. Among the most common tasks, one can note a kind of separation effect of fat globules in diameter, which allows cream to be formed. This process also ensures the stability of the fat in the raw product. To understand the significance of homogenization, it is worth noting that the volume and number of fat globules in raw milk are not constant - these characteristics are determined by the diet, lactation stage and breed of the animal. For example, 1 mm of a fresh dairy product contains up to 4 billion fat globules with an average diameter of about 2-3 microns with fluctuations from 0.5 to 15 microns. The main purpose of milk homogenization as one of the initial processes of processing raw materials in the manufacture of cheese, cottage cheese, fermented baked milk, etc. lies in ensuring the uniformity of the sizes of these balls. 1 µm.

Requirements for the homogenization process

The considered method of dairy processing cannot be considered in isolation from the associated technological processes of preparing the product for final production. In particular, milk homogenization is a procedure that can be associated with storage, transportation and subsequent pasteurization operations. Accordingly, there are universal general requirements for milk processing, which are more related to sanitary and hygienic standards, but there are also special rules for performing homogenization. Among them are the following:

• Before processing, raw milk undergoes primary filtration and cooling.
• The temperature of the milk should vary between 4 and 6 °C. The specific mode will determine the allowable storage time before and after processing - as a rule, no more than 6 hours.
• The average pressure during milk homogenization is 10 MPa. At the same time, in order to normalize the heterophase structure, it may be necessary to increase the phase separation by 500 thousand m 2 for each ton of raw materials.
• Homogenization is performed before pasteurization. Exceptions may be if the operation is carried out at 60 ° C. This mode is usually used when obtaining skimmed milk and cream, but in this technological scheme, after homogenization, additional pasteurization will follow.

Applied equipment

Technically, the operation is performed by the action of an external force, the source of which is a homogenizer. This is a special machine that acts on the target product with mechanical pressure, electricity or ultrasound. More often used units with a mechanical principle of operation. The main working element of such equipment for milk homogenization is a head with an annular valve slot, through which fat globules are passed. Power support is provided by a pump, the power of which allows you to create pressure up to 20 MPa. It is enough to reduce the balls to 0.7 microns, but, as already mentioned, a pressure mode of 10 MPa is more often used, at which fatty particles with a fraction of 1-2 microns are released. Different models of homogenizers have a one- or two-stage design. Accordingly, one or two products (with different degrees of fat content) can be produced at the same time.

General Homogenization Technique

After preliminary preparation of raw milk for mechanical separation, the following list of actions is performed:

• Mixing of a dispersion medium with a liquid dispersion system at the dispersant capacity.
• The dairy medium is pumped under pressure through the homogenizer heads. The fatty dispersed phase is crushed to the desired fraction.
• A more subtle process of milk homogenization, involving the mixing of small fat fractions in special mixers.
• Heat pasteurization.
• Product cooling.

Auxiliary or intermediate operations can be used between technological stages in different sequences. This applies to heating, cleaning and sterilization.

Complete homogenization

This method of homogenization is considered the most common in industries where drinking dairy products are produced. The main feature of the method is the exclusion of phase separation. In other words, the whole milk raw mass is subjected to the crushing process without preliminary separation. Complete homogenization of milk is also the best way to obtain a normalized dry fat-free residue, which can later be used in the manufacture of yoghurts.

Separate homogenization

This method is also widely used, but is considered more specialized. The fact is that the process of separate homogenization is focused on working with a certain part of the loaded raw mass. For example, a certain proportion of a fatty product is allocated according to specific characteristics. In the classical scheme, the main part of skimmed milk is cut off, but there are also intermediate methods of separation and further homogenization, in which the separation takes place according to specific fat parameters. Among the advantages of this technique, it is noted not only the possibility of obtaining a better product, but also the cost-effectiveness of the process. The highest coefficient of efficiency of milk homogenization with separation of fractions is achieved if there is at least 0.2 g of casein per 1 g of fat.

Milk temperature during homogenization

One of the most important parameters that also determines the degree of quality of the final product and the efficiency of the entire process. Suffice it to say that a critical decrease in the temperature regime can lead to an increase in the viscosity of raw milk and the formation of dense fat accumulations. As a minimum, to ensure cream settling, the milk homogenization temperature should be 30-40 °C.

But also too high temperatures can adversely affect the physicochemical state of the heterophase medium. In this case, protein deposits may form on the working surfaces of the equipment, which will complicate the process of mechanical operations. To regulate the thermal degree of milk homogenization, intermediate pasteurization means are used with a gradual increase in temperature by 5-8 °C. At the same technological stage, sterilization operations and thermal vacuum treatment can be used if there is a need to adjust other milk parameters.

Effects of homogenization

From the point of view of food production and consumer qualities, this processing technology helps to ensure the following product properties:

• For cream and milk - increasing uniformity (in color, taste and fat content).
• For sterilized cream and dairy products - an increase in the storage period.
• For whole milk powder - regulation of acidity and fat.
• For fermented milk products - exclusion of fatty plugs on the surface, increased durability, improved protein consistency.
• For condensed products - during long-term storage, the natural regulation of the release of fatty phases.
• For dairy products with fillers - increasing viscosity, improving taste and minimizing the risk of sedimentation.

In general, it can be said that properly organized processes of sterilization, homogenization and pasteurization of milk comprehensively affect the biological and physico-chemical properties of raw materials, which affect the content and gastronomic qualities of the processed product.

Quality control of homogenized raw milk

After mechanical processing, the characteristics of the dairy product are monitored. In particular, indicators such as mass fraction of fat, degree of purity, etc. are taken into account. As for the fat fraction, it is determined by metric, express and acid methods. For example, the last method is the most popular. It involves mixing a certain dose of milk with concentrated sulfuric acid, followed by centrifugation. Further, by means of the graduated part of the butyrometer in the control equipment, the volume of released fat is determined.

The purity of milk is determined by special filters, complemented by a needle-punched thermal cloth. The degree of purity of the product is fixed by the volume of impurities. Complex analysis tools are also involved. Using a milk homogenization pipette with a division value of about 0.1 cm 3, samples are taken, which are then tested by heating, chemical and biological reactions. Finally, a laboratory report is made on the characteristics of the homogenized dairy product.

Conclusion

With all the positive effects of homogenization, many experts are critical of it because of the production of harmful enzymes. However, at the moment there are no reliable studies that would reveal a significant difference for human health between a natural and a dairy product processed in this way. Moreover, today the homogenization of milk is a complex of production processes that have become a necessity in the food industry. This method of mechanical processing is used not only in relation to fresh milk, but also in the recovery of dried milk raw materials by adjusting the degree of fat content. Another thing is that in each case, modifying chemical additives are also used, the presence of which in the product, in principle, reduces its value.

Homogenization has become a standard manufacturing process commonly practiced as a means of keeping the fat emulsion from separating by gravity. Gaulin, who developed this process in 1899, gave it the following definition in French: "Fixer la composition des liquides".

First, homogenization leads to the splitting of fat globules into much smaller ones (see Fig. 1). As a result, creaming is reduced and the tendency of the balls to stick together or form large agglomerates can also be reduced. Basically, homogenized milk is produced mechanically. It is driven at high speed through a narrow channel.

The destruction of fat globules is achieved by a combination of factors such as turbulence and cavitation. As a result, the diameter of the balls decreases to 1 micron, and this is accompanied by a four to six-fold increase in the area of ​​the intermediate surface between fat and plasma. As a result of the redistribution of the shell substance, which completely covered the fat globules before their destruction, the newly formed globules have insufficiently strong and thick shells. These membranes also include adsorbed milk plasma proteins.

Fox, along with his colleagues, investigated the fat-protein complex obtained by homogenizing milk. He proved that casein is the protein component of the complex and that it is possibly associated with the fat fraction through polar attractive forces. He also found that the casein micelles are activated as they pass through the homogenizer valve, predisposing them to interact with the fat phase.

Process Requirements

The physical condition and concentration of the fat fraction during homogenization affect the size of the fat globules. Homogenization of cold milk, in which fat is mainly present in a solidified state, is practically not feasible. Processing milk at a temperature of 30-35°C leads to incomplete dispersion of the fat fraction. Homogenization is truly effective when the entire fat phase is in a liquid state, and at concentrations that are normal for milk. Foods with a high fat content tend to form large fat globules, especially at low whey protein concentrations with a high fat content. Cream with a fat content greater than 12% cannot be successfully homogenized at standard elevated pressure because the lack of membrane material (casein) causes the fat globules to stick together into clusters. For sufficiently effective homogenization, one gram of fat should have 0.2 grams of casein.

High pressure homogenization processes result in the formation of small fat globules. With an increase in the homogenization temperature, the dispersity of the fat phase increases - in proportion to the decrease in the viscosity of milk at elevated temperatures.

Usually homogenization is carried out at a temperature of 55 to 80°C, under a pressure of 10 to 25 MPa (100-250 bar), depending on the type of product being processed.

Flow Characteristics

When the flow passes through a narrow channel, its speed increases (see Fig. 2). The speed will increase until the static pressure decreases to a level at which the liquid boils. The maximum speed mainly depends on the inlet pressure. As the fluid leaves the slot, the velocity decreases and the pressure begins to rise. The boiling of the liquid stops and the vapor bubbles explode.

Homogenization theories

Over the years of application of the homogenization process, many theories have arisen that explain the mechanism of homogenization at high
pressure. Two theories explaining the dispersed oil-water system by analogy with milk, where the diameter of most droplets is less than 1 micron, have not become obsolete to date.
They provide an explanation of the influence of various parameters on the efficiency of homogenization.

The theory of the destruction of balls by turbulent whirlpools (“microvortices”) is based on the fact that a large number of turbulent microflows arise in a liquid moving at high speed.

If a turbulent microflow collides with a drop comparable to it, the latter is destroyed. This theory makes it possible to predict changes in the results of homogenization with changes in the applied pressure. This link has been found in many studies.

On the other hand, the theory of cavitation states that fat droplets are destroyed by shock waves that occur when steam bubbles explode. According to this theory, homogenization occurs when the liquid leaves the gap. Thus, the back pressure required for cavitation is of great importance in this case. This has been confirmed in practice. However, homogenization is possible without cavitation, but in this case it is less effective.

Fig.3 Destruction of fat globules at the first and second stages of homogenization.
1 After the first stage
2 After the second stage

One-stage and two-stage homogenization

Homogenizers can be equipped with one homogenizing head or two connected in series. Hence the name: single-stage homogenization and two-stage homogenization. Both systems are shown in figures 5 and 6. In single-stage homogenization, the entire pressure drop is used
in a single step. With two-stage homogenization, the total
the pressure is measured before the first stage P 1 and before the second stage P 2 .

For optimum homogenization efficiency, a two-stage variant is usually used. But the desired results can be obtained if the ratio P 2: P 1 is approximately 0.2. One-stage version is used for homogenization

• low fat products
• products requiring high viscosity (formation of certain agglomerates).
• in products requiring low viscosity
• to achieve maximum efficiency of homogenization (micronization).

Figure 3 shows the formation and destruction of accumulations of fat globules in the second stage of homogenization.

Influence of homogenization on the structure and properties of milk

The effect of homogenization has a positive effect on the physical structure
and properties of milk and is manifested in the following:

• Reducing the size of the fat globules, which prevents the cream from settling
• Whiter and appetizing color
• Increased resistance to fat oxidation
• Improved aroma and taste
• Increased safety of fermented milk products made from homogenized milk.

However, homogenization also has certain disadvantages. Among them:

• Impossibility of separation of homogenized milk
• Slightly increased sensitivity to light, both from the sun and from fluorescent lamps, can lead to a so-called sunny taste.
• Reduced heat resistance - especially pronounced when testing the first stage of homogenization, homogenization of skimmed milk and in other cases that contribute to the formation of accumulations of fat globules
• The unsuitability of milk for the production of semi-hard and hard cheeses, since the clot will not separate whey well.

Homogenizer

High pressure homogenizers are usually required to ensure maximum homogenization efficiency.

The product enters the pumping unit, where it is pressurized by a piston pump. The level of pressure generated depends on the back pressure, determined by the distance between the piston and the seat in the homogenizing head. The pressure P 1 always means the pressure of homogenization. P 2 is the back pressure of the first stage of homogenization or the pressure at the inlet to the second stage.

Fig.4 The homogenizer is a large high pressure pump with a back pressure device.
1 Main drive motor
2 V-belt drive
3 Pressure gauge
4 Crank mechanism
5 piston
6 Piston seal
7 Cast stainless steel pump block
8 Valves
9 Homogenizing head
10 Hydraulic system

Fig.5 Single-stage homogenization. Schematic of the homogenizing head:
1 valve
2 Impact ring
3 Saddle
4 Hydraulic drive

High pressure pump

The piston pump is driven by a powerful electric motor (pos. 1 in Fig. 4) through the crankshaft and connecting rods - this transmission converts the rotation of the engine into reciprocating motion of the pump pistons.

The pistons (pos. 5) move in the high pressure cylinder block.
They are made from high strength material. The pistons are equipped with double seals. Water is supplied to the space between the seals to cool the pistons. Hot condensate can also be supplied there to prevent re-contamination of the product with microorganisms during the operation of the homogenizer. It is also possible to use hot condensate to maintain the conditions of aseptic production of the product during the operation of the homogenizer.

Homogenizing head

Figures 5 and 6 show the homogenizing head and its hydraulic system. The piston pump raises the milk pressure from 300 kPa (3 bar) at the inlet to a homogenization pressure of 10-15 MPa (100-240 bar), depending on the type of product. The pressure at the inlet to the first stage before the mechanism (homogenization pressure) is automatically kept constant. The oil pressure on the hydraulic piston and the homogenizing pressure on the valve balance each other. The homogenizer is equipped with one common oil tank, regardless of whether it is a single-stage or two-stage version. However, in a two-stage homogenizer, there are two hydraulic systems, each with its own pump. The new homogenization pressure is set by changing the oil pressure. The homogenizing pressure is indicated on the high pressure gauge.

The homogenization process takes place in the first stage. The second mainly serves two purposes:

Creating a constant and controlled back pressure towards the first stage, thus ensuring optimal homogenization conditions

Destruction of sticky clusters of fat globules that form immediately after homogenization (see Fig. 3).

Note that the homogenization pressure is the pressure before the first stage, not the differential pressure.

The parts of the homogenizing head are machined on a precision grinding machine. The shock ring is seated in its place in such a way that its inner surface is perpendicular to the slot exit. The seat is beveled at a 5 degree angle to give the product a controlled acceleration, thus preventing the accelerated wear that would otherwise be inevitable.

Milk under high pressure penetrates between the seat and the valve. The gap width is approximately 0.1 mm, which is 100 times the diameter of the fatty pressure produced by the piston pump, converted into kinetic energy. Part of this energy after passing through the mechanism is again converted into pressure. The other part is released as heat; every 40 bar pressure drop after passing through the mechanism raises the temperature by 1°C. Homogenization consumes less than 1% of all this energy, and yet high pressure homogenization is still the most efficient method available today.

Fig.6
two-stage homogenization.
1 First step
2 Second step

Homogenizing efficiency

The purpose of homogenization depends on how it is applied. Accordingly, the methods of evaluating effectiveness are also changing.

In accordance with the Stokes law, the growing speed of a particle is determined by the following formula, where: v is the speed

q is the acceleration due to gravity p is the size of the particle η hp is the density of the liquid η ip is the density of the particle t is the viscosity

Or v = constant x p 2

It follows from the formula that reducing the particle size is an effective way to reduce the increase in velocity. Therefore, a decrease in the particle size in milk leads to a slowdown in the rate of cream settling.

Analytical Methods

Analytical methods for determining the efficiency of homogenization can be
divided into two groups:

I. Determination of the cream settling rate

The oldest way to determine cream settling time is to take a sample, let it sit for a certain amount of time, and then analyze the fat content of the different layers. The USPH method is based on this principle. For example, a one liter sample is aged for 48 hours, after which the fat content in the top layer (100 ml) is determined, as well as in the rest of the milk. Homogenization is considered satisfactory if the mass fraction of fat in the lower layer is 0.9 times less than in the upper layer.

The NIZO method is based on the same principle. According to this method, a sample of, say, 25 ml is subjected to centrifugation for 30 minutes at 1000 rpm at 40°C and a radius of 250 mm. The fat content of the 20 ml bottom layer is then divided by the fat content of the entire sample and the result is multiplied by 100. This ratio is called the NIZO value. For pasteurized milk, it is usually 50-80%.

II. Fractional Analysis

The size distribution of particles or droplets in a sample can be determined by a well-established method using a laser diffraction setup (see Fig. 7), which sends a laser beam into the sample in the cuvette. The degree of light scattering will depend on the size and number of particles contained in the milk under study.

The result is shown in the form of particle size distribution graphs. Fat percentage by mass is presented as a function of particle size (fat globule size). Figure 8 shows three typical fat globule size distribution graphs. Note that as the homogenization pressure increases, the graph shifts to the left.

Energy consumption and its effect on temperature

The electrical power input required for homogenization is expressed by the following formula:

Homogenizer in the production line

Usually the homogenizer is installed at the beginning of the line, i.e. before the final heating section in the heat exchanger. In most pasteurization plants for the production of drinking milk for the consumer market, the homogenizer is located after the first regenerative section.

In the production of sterilized milk, the homogenizer is usually placed at the beginning of the high-temperature treatment process in an indirectly heated system, and always at the end of the process in a direct product heating system, i.e. in the aseptic part of the plant after the product sterilization section. In this case, an aseptic version of the homogenizer is used, equipped with special piston seals, gaskets, a sterile condenser and special aseptic dampers.

An aseptic homogenizer is installed after the sterilization section of units with direct product heating in cases of production of dairy products with a fat mass fraction of more than 6-10% and/or with a high protein content. The fact is that at very high processing temperatures in milk with a high content of fat and / or proteins, accumulations of fat globules and casein micelles are formed. An aseptic homogenizer located after the sterilization section breaks down these agglomerated particles.

Complete homogenization

Full homogenization is the most common method for homogenizing drinking milk and milk intended for the production of fermented milk products. The fat content of milk, and sometimes the content
dry fat-free residue (in the production of yogurt, for example) are normalized before homogenization.

Separate homogenization

Separate homogenization means that the bulk of the skimmed milk is not homogenized. Cream and a small amount of skimmed milk are homogenized. This homogenization method is usually used for pasteurized drinking milk. The main advantage of separate homogenization is its relative economy. The total energy consumption is reduced by up to 65% due to less milk passing through the homogenizer.

Since the highest homogenization efficiency can be achieved if the milk contains at least 0.2 g of casein per 1 g of fat, the recommended maximum fat content is 12%. The hourly output of a plant in which separate homogenization is carried out can be determined by the following formula.

The production of pasteurized normalized milk (Q sm) per hour will be approximately 9690 liters. If we substitute this figure into formula 2, we get,
that the hourly output of the homogenizer is approximately 2900 liters,
that is, about a third of its total performance.

The scheme of flows in the installation for partially homogenized milk is shown in Fig.10.

The effect of homogenized dairy products on the human body

In the early 1970s, the American scientist K. Oster (K. Oster) came up with a hypothesis that the homogenization of milk allows the xanthine oxidase enzyme to penetrate through the intestines into the circulatory system. (Oxidase is an enzyme that catalyzes the addition of oxygen to or the removal of hydrogen from a substrate.) According to Oster, xanthine oxidase contributes to the process of damage to blood vessels and leads to atherosclerosis.

This hypothesis was rejected by scientists on the grounds that the human body itself produces thousands of times more of this enzyme than homogenized milk could theoretically bring into it.

So, there can be no harm from homogenizing milk. From a nutritional point of view, homogenization does not bring any special changes, except, perhaps, that fat and protein are broken down faster and easier in homogenized products.

However, Oster is right that oxidation processes can be harmful to the human body and that diet is important for health.

Homogenization is the crushing (dispersion) of fat globules by exposing milk or cream to significant external forces. During processing, the size of the fat globules and the speed of ascent are reduced. There is a redistribution of the shell substance of the fat globule, the fat emulsion is stabilized, and the homogenized milk is not settled.

Valve-type homogenizers are used to process milk and cream in order to prevent their separation during storage.

Homogenizers-plasticizers of the rotary type are used to change the consistency of dairy products such as processed cheeses and butter. In the butter processed with their help, the aqueous phase is dispersed, as a result of which the product is better stored.

The principle of operation of valve-type homogenizers, which are most widely used, is as follows. In the cylinder of the homogenizer, milk is subjected to mechanical action at a pressure of 15...20 MPa. When the valve is lifted, slightly opening a narrow gap, the milk comes out of the cylinder. This is possible when the operating pressure in the cylinder is reached. When passing through a narrow circular gap between the seat and the valve, the speed of milk increases from zero to a value exceeding 100 m/s. The pressure in the flow drops sharply, and a drop of fat that has fallen into such a flow is drawn out, and then, as a result of the action of surface tension forces, it is crushed into small droplets-particles.

During the operation of the homogenizer at the outlet of the valve gap, adhesion of crushed particles and the formation of "clusters" are often observed, which reduce the efficiency of homogenization. To avoid this, two-stage homogenization is used. At the first stage, a pressure equal to 75% of the working one is created, at the second stage, the working pressure is set.

Rice. 2.22. Homogenizing head

For homogenization, the temperature of raw milk should be 60...65 °C. Lower temperatures increase fat settling, while higher temperatures can precipitate whey proteins.

A homogenizer with a two-stage homogenizing head consists of a frame, a body, a plunger block, a homogenizing head, a drive and a crank mechanism.

Fig.2.23. Homogenizer A1-OGM-5:

1 - electric motor; 2 - bed with a drive; 3 - crank mechanism with lubrication and cooling systems; 4 - plunger block with homogenizing and manometric heads and safety valve; 5 - manometric head; 6- homogenizing head; 7- V-belt transmission

In the case when during homogenization it is necessary to exclude the access of microorganisms to the processed product, special aseptic homogenizing heads are used. In such heads, the space limited by two sealing elements is supplied with hot steam at a pressure of 30...60 kPa. This high temperature zone acts as a barrier to prevent bacteria from entering the homogenizer barrel.

Homogenizers-plasticizers differ from valve-type homogenizers in terms of the principle of operation and device. The working body in them is the rotor, which can have a different number of blades - 12, 16 or 24.

The homogenizer-plasticizer consists of a frame, a body with screws, a receiving hopper and a drive.

Fig.2.24. Homogenizer Homogenizing Tool Kit:

1-fixed ring; 2- movable ring; 3 - paddle wheel; 4- bunker; 5 - movable knife; 6- body; 7- fixed knife; 8- unloading rotor; 9- homogenizer shaft

The drive allows you to adjust the frequency of rotation of the feed screws (with the help of a variator) within 0.2 ... 0.387 s 1 . The speed of the rotor with the blades is not adjustable and is 11.86 s".

The principle of operation of the machine is as follows. Butter is fed into the bunker, from where, with the help of two counter-rotating screws, it is forced through the rotor and exits from the nozzle with a diaphragm into the bunker of the filling machine. To prevent sticking of oil, the working parts of the homogenizer are lubricated with a special hot solution before starting work. The performance of the homogenizer depends on the frequency of rotation of the feed screws and is 0.76 ... 1.52 m 3 / h. The drive power of the machine is 18.3 kW.

Homogenizer YaZ-OGZ is designed for processing melted cheese mass in the production of processed cheese and consists of the following parts: base, housing, set of homogenizing tools, hopper, unloading device and drive.

The base serves to attach the components of the homogenizer to it. The housing contains working units and sealing devices.

The homogenizing tool for feeding, grinding and mixing the molten cheese mass is made in the form of movable and fixed knives separated by spacer rings, as well as a loading impeller and an unloading rotor. Movable knives have special grooves made at a certain angle to the end surface, which facilitates the movement of the crushed product to the unloading device. The shaft of the homogenizing tool rotates with a frequency of 49s 1 .

The bunker for receiving and accumulating cheese mass has a heat-insulating jacket.

The unloading device in the form of two pipes connected to each other by means of a crane serves to discharge the homogenized mass into the batcher of the filling machine.

The drive consists of an 11 kW motor designed to transmit rotation from the shaft to the moving part of the homogenizing tool.

Processing of the product on the homogenizer YAZ-OGZ is carried out as follows. The melted cheese mass is periodically or continuously fed into the homogenizer hopper. Under the action of vacuum created by the loading paddle wheel, the product enters the homogenizing tool, in which, passing sequentially through the movable and fixed knives, it is homogenized and fed to the unloading device.

The use of a homogenizer makes it possible to abandon the technological operation of filtering the cheese mass in order to remove its unmelted particles.

This method of mechanical processing of milk and liquid dairy products serves to increase the dispersion of the fat phase in them, which makes it possible to exclude the settling of fat during storage of milk, the development of oxidative processes, destabilization and churning during intensive mixing and transportation.

Homogenization of raw materials contributes to:

in the production of pasteurized milk and cream - the acquisition of uniformity (taste, color, fat content);

sterilized milk and cream - increasing storage stability;

fermented milk products (sour cream, kefir, yogurt, etc.) - increasing the strength and improving the consistency of protein clots and eliminating the formation of a fatty plug on the surface of the product;

condensed milk canned food - preventing the release of the fatty phase during long-term storage;

whole milk powder - reducing the amount of free milk fat, not protected by protein shells, which leads to its rapid oxidation under the action of atmospheric oxygen;

reconstituted milk, cream and fermented milk drinks - to create a full taste of the product and prevent the appearance of a watery aftertaste;

milk with fillers (cocoa etc.) - improving taste, increasing viscosity and reducing the likelihood of sediment formation.

Dispersion of fat globules, i.e., reduction in their size and uniform distribution in milk, is achieved by exposing milk to a significant external force (pressure, ultrasound, high-frequency electrical processing, etc.) in special machines - homogenizers.

The most widespread in the dairy industry is the homogenization of milk by forcing it through the annular valve slot of the homogenizing head of the machine. Fat globules, passing through this gap, are dispersed. The required pressure is generated by a pump. In the production of whole milk, the size of fat globules decreases from 3-4 microns to 0.7-0.8 microns.

The main unit of modern valve-type homogenizers is the homogenizing head. It can be one or two stages. The second stage usually operates at a lower pressure than the first.

The use of one- or two-stage homogenization depends on the type of dairy products being produced.

Two-stage homogenization with a large pressure drop on both stages is used in the production of high-fat dairy products (cream, ice cream mixtures, etc.).

It allows you to disperse (break) the resulting accumulations of fat globules. For the production of other types of dairy products, including drinking milk, one-stage homogenization can be used.

Heat treatment of milk

Heat treatment is one of the main and necessary technological operations of milk processing, carried out for the purpose of disinfection. The efficiency of heat treatment is related to the heat resistance of milk, which is determined by its protein, salt composition and acidity, which, in turn, depend on the season, lactation period, physical condition and breed of animals, feeding regimes and diet, etc.

During heat treatment, milk and dairy products undergo complex changes in biochemical and physico-chemical properties, as well as modifications of the components of milk. The purpose of heat treatment is diverse, namely: reducing the total number of microorganisms and destroying pathogenic forms, inactivating (destroying) milk enzymes to increase stability during long-term storage, providing specific taste, smell, color and texture, creating favorable temperature conditions for fermentation, evaporation, storage, as well as mechanical processing processes, etc.

Heat treatment of milk is a combination of temperature exposure modes (heating or cooling) and exposure time at this temperature. Moreover, the duration of exposure at a given temperature should be such that the desired effect is obtained. In the dairy industry, heat treatment is carried out at temperatures up to 100 and over 100 °C.

When heated to 100 °C, only vegetative forms die in milk, and at temperatures above 100 °C, vegetative and spore forms die. The main processes of heat treatment of milk, causing the suppression of the vital activity of microorganisms, are pasteurization and sterilization. Hot water and saturated water steam are used as a heat carrier for pasteurization, and saturated water steam is used for sterilization.

In addition, during heat treatment, milk is subjected to cooling, heating (heating), thermal vacuum treatment.

The mode of heat treatment of milk for the production of each type of product is determined by the technological instruction. In this case, the milk is heated to the pasteurization temperature, and then kept and quickly cooled to the required temperature. The combination of heating and cooling operations is dictated by technological and sanitary requirements, as well as the possibility of using the heat of a hot product.

To do this, the hot product is sent to a special section of the apparatus (plate or tubular) for preheating the cold product entering the pasteurization. This operation is called heat recovery, and the apparatuses or their parts are called regenerators or regeneration sections. The use of this operation allows you to get some savings in thermal energy spent on pasteurization.

The efficiency of the regenerator is characterized by the regeneration coefficient. It represents the ratio of the amount of heat returned by the regenerator to the amount of heat required to heat the product from the initial to the final temperature, i.e., at which the product begins to reverse movement through the regenerator.

Cooling and heating

Dairy raw materials are cooled at the enterprises in order to preserve its quality and limit the growth of the number of microorganisms before processing. In table. 4.1 shows data showing the growth of the number of microorganisms in milk depending on the temperature of cooling and the duration of storage.

Storage of milk at temperatures above 4.5 °C leads to an increase in the number of microorganisms. In practice, milk for short-term storage is cooled to 6--8 °C. For long-term storage (10-14 hours), milk is pasteurized and then cooled. In order to increase the shelf life of dairy products, they are cooled during the manufacturing process.

Heating (heating) does not play the main role, but most often performs an auxiliary (preparatory) function in the process of milk processing. Heating of milk is used before separation, homogenization, as well as in the production of various dairy products. During separation, heating milk reduces its viscosity properties, which has a positive effect on the separation of fat globules from the milk plasma and the formation of cream.