Raw milk goes through several stages of preparation before entering the conventional conveyor of the food industry. At the moment there are several groups of chemical, thermal and biological processing operations. A special place in the overall complex of preparation of a raw material product is occupied by the homogenization of milk. This is a machining technology, but depending on the particular methodology, it may also include separate thermal and chemical treatments.
General homogenization
In principle, this technology is used as a method for the mechanical processing of dairy and other liquid products in order to increase the dispersion of their fat phase. During the process, the heterogeneity of the distribution of chemical elements throughout the entire volume of the heterophase system also decreases. In this case, do not confuse this technique with dispersion as such. According to the definition of milk homogenization, crushing of the dispersed phase is not a prerequisite for the technological process. For example, the procedure for mixing solid powdery substances may well exclude this operation. Conversely, dispersing a heterophasic system may imply and also exclude the homogenization procedure.
Technology purpose
The goals of homogenization may vary depending on the current condition of raw milk and the requirements for the final product. Among the most common tasks, one can note a kind of effect of separation of fat globules by diameter, which allows the formation of cream. This process also ensures the stability of fat in the raw material. To understand the significance of homogenization, it is worth noting that the volume and quantity of fat globules in raw milk are variable - these characteristics are determined by the diet, the stage of lactation and the breed of the animal. For example, 1 mm of 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 the homogenization of milk 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 values of these balls. Moreover, the averaging and alignment of dimensional parameters is usually achieved by reducing fat globules by a factor of 10 — to about 1 micron.
Homogenization process requirements
The considered method of milk processing cannot be considered in isolation from the associated technological processes of preparing the product for final production. In particular, the homogenization of milk is a procedure that may be associated with the operations of storage, transportation and subsequent pasteurization operations. Accordingly, there are universal general requirements for the processing of milk, which relate more to sanitary standards, but there are special rules for performing homogenization. Among them are the following:
- Before processing, milk raw materials undergo primary filtration and cooling.
- The temperature of milk should vary in the range from 4 to 6 ° C. The specific mode will determine the permissible storage time before and after processing - usually no more than 6 hours.
- The average pressure during homogenization of milk is 10 MPa. Moreover, to normalize the heterophase structure, it may be necessary to increase the phase separation by 500 thousand m 2 for each ton of raw material.
- Homogenization is performed before pasteurization. Exceptions may be made if the operation is carried out at 60 ° C. This mode is usually used to obtain skim milk and cream, but even in this process scheme after homogenization, additional pasteurization will follow.
Applied Equipment
Technically, the operation is performed by external force, the source of which is a homogenizer. This is a special machine acting 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 the homogenization of milk is the head with an annular valve slit through which fat globules are passed. Power support is provided by a pump, the power of which allows you to create a pressure of up to 20 MPa. It is enough to reduce the balls to 0.7 μm, but, as already mentioned, a pressure mode of 10 MPa is more often used, in which fat particles of a fraction of 1-2 μm are released. Different models of homogenizers have a one- or two-stage design. Accordingly, one or two products (with varying degrees of fat content) can be produced simultaneously.
General homogenization technique
After preliminary preparation of milk raw materials for mechanical separation, the following list of actions is performed:
- Mixing the dispersed medium with a liquid dispersion system at the power of the dispersant.
- The dairy medium is pumped under pressure through the heads of the homogenizer. The dispersed fat phase is milled to the desired fraction.
- A more subtle process of homogenization of milk, involving the mixing of small fat fractions in special mixers.
- Thermal pasteurization.
- Product cooling.
Between the technological steps, auxiliary or intermediate operations in different sequences can be applied. 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 entire milk raw material mass is subjected to crushing without prior separation. Complete homogenization of milk is also an optimal way to obtain a normalized dry skimmed residue, which can later be used in the manufacture of yoghurts.
Separate homogenization
This method is also widespread, but is considered more specialized. The fact is that the process of separate homogenization focuses on working with a certain part of the loaded raw material mass. For example, a certain proportion of a fat product is released according to specific characteristics. In the classical scheme, the bulk of skim milk is cut off, but there are intermediate methods of separation and further homogenization, in which separation takes place according to specific parameters of fat. Among the advantages of this technique is noted not only the possibility of obtaining a better product, but also the efficiency of the process. The highest coefficient of milk homogenization efficiency with separation of fractions is achieved if at least 0.2 g of casein is per 1 g of fat.
Milk temperature during homogenization
One of the most important parameters, also determining the degree of quality of the final product and the efficiency of the whole 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 thick fat accumulations. At a minimum, to ensure the settling of the cream, the homogenization temperature of the milk 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 mechanically performing operations. To regulate the thermal degree of homogenization of milk, intermediate means of pasteurization 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 applied if there is a need to adjust other parameters of milk.
Homogenization effects
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, an increase in uniformity (in color, taste and fat content).
- For sterilized cream and dairy products - increase the storage period.
- For whole milk powder - regulation of acidity and fat.
- For fermented milk products - the exclusion of fatty plugs on the surface, increased resistance, improved protein consistency.
- For condensed foods - during prolonged storage, the natural regulation of the release of fatty phases.
- For dairy products with fillers - increasing the viscosity, improving the taste and minimizing the risk of sediment formation.
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 machining, 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 latter method is the most popular. It involves mixing a certain dose of milk with concentrated sulfuric acid during subsequent centrifugation. Further, by means of the graduated part of the butyrometer in the control equipment, the volume of released fat is determined.
Milk purity is determined by special filters supplemented with needle-punched thermo-cloth. The volume of impurities is fixed degree of purity of the product. Integrated analysis tools are also involved. Using a pipette for homogenizing milk with a division value of about 0.1 cm 3, samples are taken, which are subsequently tested by heating, chemical and biological reactions. Ultimately, 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 the natural and processed milk product 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 mechanical processing method is used not only in relation to fresh milk, but also in the restoration of dry milk raw materials by regulating 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.