Milk and products obtained from its separation and used as animal feed are subject to mandatory pasteurization in the same way as drinking milk and milk from which dairy products are prepared. Milk intended for the production of fermented milk cheeses is pasteurized in the same way as drinking milk; while milk for making Emmental and mountain cheeses should not be heated to the protein coagulation temperature. When making other cheeses using rennet, milk is heat treated, although this is not provided for by the technology.
Heat treatment of milk primarily serves to destroy pathogens. In addition, it helps to significantly reduce the number of microorganisms that disrupt technological processes, increases the stability of milk and improves its technological properties. Heat treatment should ensure reliable suppression of the vital activity of microorganisms without significant changes in the properties of the milk itself.
According to current legislation, the following methods of heat treatment of milk are used: long-term, short-term, high-temperature, ultra-high-temperature.
During long-term low-temperature pasteurization, milk is heated in large double-walled baths with stirrers at a temperature of 62-65°C for 30 minutes.
Long-term pasteurization is a reliable way to suppress pathogens and only slightly changes the properties of milk. The vital activity of microbes is suppressed by almost 90%. Since long-term pasteurization is labor-intensive, this method is used very rarely.
Short-term high-temperature pasteurization of milk is carried out by heat exchange in plate pasteurizers. During short-term pasteurization, milk is heated to a temperature of 71-74°C and held for 40 s. During pasteurization, milk in a thin layer (no more than 3 mm) is passed through stainless steel plates, on the other side of which the coolant moves in countercurrent. The plates in a group are connected in parallel. The milk travels a certain path through the channels between the plates, while in direct-flow systems the milk is supplied along the shortest route to the embossed surface of the plates, where turbulence (vortices) is formed.
The plate pasteurizer consists of different sections through which the milk is passed. A plate cooler is also installed in the pasteurizer system.
The milk to be pasteurized is passed through the first heat exchanger, in which it is heated to a temperature of approximately 45 ° C. The preheated milk is then supplied to a centrifuge and, after centrifugation, is sent to the second heat exchanger 4, in which the temperature of the milk is raised to almost 62 ° G. B In the first and second heat exchangers, the milk is heated due to the heat generated by already pasteurized milk, which moves in countercurrent.
From the second heat exchanger, the heated milk enters the pasteurizer, in which it is heated to a temperature of 71-74°C through short-term pasteurization.
At this temperature the milk is kept for 30-40 s. The milk then passes through the first and second heat exchangers, where it transfers heat to the next portion of milk. In heat exchangers, the temperature of the milk is reduced to 20°C. In the refrigerator, the milk is further cooled in two stages: first with well water - to a temperature of 12 ° C, and then with water with ice or brine - to 2-4 ° C.
During short-term pasteurization, the plate pasteurizer is heated with hot water. With such pasteurization, saprophytic microflora is destroyed by 98%.
With high-temperature pasteurization, milk is heated instantly to a temperature of at least 85°C without holding it. High-temperature pasteurization is carried out according to the same principle as short-term pasteurization, but without holding. With high-temperature pasteurization, heating can be carried out not only with hot water, but with steam. The saprophytic microflora of milk during high-temperature pasteurization is suppressed by approximately 99.5%.
Currently, high-temperature pasteurization is used very rarely in the processing of milk, but it is recommended for the pasteurization of cream, from which high-quality butter is produced.
The cream used for whipping is heated in special pasteurizers to a temperature of more than 100°C in order to increase its stability and whipping ability.
In ultra-high temperature pasteurization, milk is heated in flow by passing steam or in flow-through sterilizers. During superpasteurization, milk preheated to a temperature of 70-80°C is heated to 135-150°C by passing steam into it. The heat exposure time is several seconds.
Cool the milk by removing steam under vacuum.
By automatically regulating the intake and removal of steam, the water balance of the milk is equalized. In another method, milk is fed into a steam environment. Here, in a special expanded vessel, which is under vacuum, excess steam is removed. For the production of ultra-pasteurized milk, flow sterilizers are used, which can be in the form of a drum, tubular or plate.
Compared to milk pasteurization, which only reduces the number of microorganisms, UHT pasteurization produces milk that is completely free of microorganisms. It is bottled in light-proof packaging. This milk can be stored at room temperature for at least 6 weeks. Sterilization of packaging material is carried out in baths with hydrogen peroxide and by heating. There should be no hydrogen peroxide left on the packaging material; it should be removed by heat treatment.
In ultra-pasteurized milk, all its natural properties - smell, taste, appearance and biological value are preserved, since heating occurs in a very short time. Milk after UHT pasteurization must be homogenized to prevent the cream from settling during long-term storage.
Sterilization of milk is carried out through long-term pasteurization in containers. Sterilization is carried out in closed sterilizers (autoclaves). The duration of sterilization in autoclaves at temperatures above 100°C ranges from 15 to 17 minutes. During continuous sterilization, milk is kept for up to 2 minutes at a temperature of 120°C. Sterilized milk should also be homogenized for long-term storage.
Homogenization of milk prevents the cream from settling. The rate at which cream settles depends on the size of the fat globules. In unprocessed milk, fat globules have a diameter of 2.5-5 (up to 8) microns; during homogenization they decrease in size. For homogenization, milk, preheated to a temperature of 40-50°C, is pumped through nozzles under high pressure. It then hits the deflector ring at a right angle. In this case, the fat globules break down, their size in diameter decreases to 0.8 microns. Fully homogenized milk should not allow cream to settle for 24 hours. When producing ultra-pasteurized milk, homogenization is carried out in two stages if possible.
With partial homogenization, only the cream is processed, to which skim milk is then added.
With complete homogenization, the fat globules in milk are separate from each other, and with partial homogenization, they form clusters (fat lumps).
Therefore, in partially homogenized milk, the cream settles relatively quickly (fat edges are formed). In addition to high pressure homogenization, low pressure homogenization and centrifugal homogenization are also used. Homogenization using ultrasound has not yet been introduced in Germany.
In homogenized milk, the cream either does not settle at all (complete homogenization) or partially settles (partial homogenization). This milk has a good taste and high digestibility.
Heat treatment or pasteurization is the process of heating milk from 63 ºС to a temperature close to the boiling point.
This process got its name from the famous French scientist Louis Pasteur (1822-1892), who first used this method to destroy microorganisms in wine and beer.
The effect of pasteurization on microorganisms contained in milk depends on the temperature to which the milk is heated and the duration of exposure at this temperature.
Pasteurization destroys microbes, and sterilization (heating milk above boiling point) also destroys spores. Boiling destroys all microflora of milk, with the exception of spores that are resistant to boiling temperatures. Pasteurization without noticeable changes in the organoleptic properties of milk (taste, smell and consistency) destroys tuberculosis, brucellosis and other pathogenic bacteria.
In ordinary collected milk, 99% of bacteria die only under the condition of good, reliable sterilization of equipment, equipment, and utensils used in the pasteurization process. Thus, the addition of contaminated milk containing 1 billion bacteria to pasteurized milk (i.e., the amount that could remain inadvertently in dairy equipment) will increase the number of bacteria in milk to 1 million in 1 ml. These bacteria will actively multiply and will inevitably lead to spoilage of all milk.
Pasteurization, therefore, is the simplest and cheapest way to decontaminate milk.
Milk is also pasteurized during the production of all dairy products in order to protect them subsequently from undesirable processes that are caused by the activity of bacteria and especially E. coli, butyric acid bacteria, etc.
When cattle are kept on pasture, the microflora of milk is destroyed by heating more completely than when kept in stalls. This is explained by the fact that when kept in stalls, bacteria enter the milk mainly from manure particles. These bacteria are more resistant to heat due to their properties. When kept on pasture, milk contains mainly bacteria that multiply on plants. Before pasteurization, thorough cleaning of milk is necessary. In practice, three pasteurization modes are used:
during long-term pasteurization, milk is heated to 63-65 º C and maintained at this temperature for 30 minutes;
short-term pasteurization is carried out at 72-75 º C with holding for 15-20 s, which is carried out in a stream;
flash pasteurization - heating milk to a temperature of 85-90 C without holding it.
Thermal effects on milk lead to some changes in its constituent substances. When heated, the gases dissolved in it evaporate from milk. Due to the removal of carbon dioxide, the acidity of milk decreases by 0.5-1 ºT.
At temperatures above 85°, casein partially changes. But milk albumin is most affected: at 60–65 °C it begins to denature.
The salt composition of milk is also disrupted during pasteurization. Soluble phosphate salts become insoluble. Due to the partial coagulation of proteins and the formation of insoluble salts, a sediment called milkstone (burnt) is deposited on the surface of heating devices (pasteurizers).
Pasteurized milk is curdled more slowly by rennet. This is explained by the precipitation of calcium salts. Adding a calcium chloride solution to such milk restores its ability to coagulate.
Vitamins are resistant to high temperatures, especially if milk is heated without access to oxygen. Heating to high temperatures (80-85°) gives milk a special taste and aroma, which intensifies as the temperature rises. When boiling, the composition of milk also changes. For example, the content of vitamins A and C is reduced by almost 2 times. Nutrients ranging from 15 to 20 are lost due to the formation of sediments of proteins, fat and calcium salts on the walls of the dishes. Therefore, there is no special need to boil pasteurized milk.
At home, we can also recommend long-term pasteurization of milk, which can be done without much difficulty. It is produced through heated water. The milk poured into the pan is stirred with a clean spoon while heating. As soon as the temperature rises to 63-65 °C, heating should be stopped and maintained for 20-30 minutes. After this, place the pan with milk in cold water.
Pasteurization of milk or heat treatment is the process of heating milk from 63 ° C to a temperature close to the boiling point.
This process got its name from the famous French scientist Louis Pasteur (1822-1892), who first used this method to eliminate microorganisms in wine and beer.
The effect of pasteurization on microorganisms present in milk depends on the temperature to which the milk is heated and the duration of exposure at this temperature.
Pasteurization destroys bacteria, and sterilization (heating milk above boiling point) immediately destroys spores. Boiling destroys all microflora of milk, except for spores that are resistant to boiling temperatures. Pasteurization without noticeable changes in the organoleptic parameters of milk (taste, smell and consistency) destroys tuberculosis, brucellosis and other pathogenic bacteria.
In ordinary collected milk, 99% of microbes die only if the equipment, tools, and utensils used in the pasteurization process are well and reliably sterilized. Thus, the addition of contaminated milk containing 1 billion microbes to pasteurized milk (i.e., the amount that could accidentally remain in dairy equipment) will increase the number of bacteria in milk to 1 million in 1 ml. These bacteria will actively multiply and will inevitably lead to spoilage of all milk.
Pasteurization is therefore a more common and cheaper method of disinfecting milk.
Milk is also pasteurized during the production of all milk products in order to protect them subsequently from undesirable processes that are caused by the activity of bacteria and especially E. coli, butyric acid microbes, etc.
In practice they are used three pasteurization modes:
- during long-term pasteurization, milk is heated to 63-65 ° C and maintained at this temperature for 30 minutes; short-term pasteurization is carried out at 72-75 °C with holding for 15-20 s, which is carried out in a stream;
- instant pasteurization - heating milk to a temperature of 85-90 ° C without holding.
The thermal effect on milk leads to some changes in its constituent substances. When heated, the gases dissolved in milk evaporate from the milk. Due to the removal of carbon dioxide, the acidity of milk decreases by 0.5-1 °T.
At temperatures above 85°, casein partly changes. But milk albumin is most affected: at 60-65 °C it begins to denature.
The salt composition of milk is also disrupted during pasteurization. Soluble phosphate salts become insoluble. Due to the partial coagulation of proteins and the formation of insoluble salts, a sediment is deposited on the surface of heating devices (pasteurizers) - milkstone (burnt).
Pasteurized milk is curdled more slowly by rennet. This is explained by the precipitation of calcium salts. Adding a calcium chloride solution to such milk restores its ability to coagulate.
On packages of store-bought milk you can see such inscriptions as: sterilized, pasteurized and ultra-pasteurized milk.
What do they all mean? In what way will milk processed for human consumption be tastier and healthier?
Milk is a unique drink with a healthy set of nutrients - proteins, fats, carbohydrates, vitamins, mineral salts.
Therefore, knowing what kind of processing it goes through before it hits store shelves is very important.
Pasteurization is the process of heating liquid products or substances once at 60 °C for 60 minutes or at a temperature of 70-80 °C for 30 minutes.
This technology was discovered in the mid-19th century by French microbiologist Louis Pasteur—hence the name.
It is used to disinfect food products, as well as to extend their shelf life.
At home, pasteurization is often used as a method for producing homemade products.
During pasteurization, the vegetative forms of microorganisms in the product die, but the spores remain in a viable state and, when favorable conditions arise, begin to develop intensively.
Therefore, pasteurized products (milk, beer, etc.) are stored at low temperatures for only a short time.
It is believed that the nutritional value of products remains virtually unchanged during pasteurization, since the taste and valuable components (vitamins, enzymes) are preserved.
Depending on the type and properties of food raw materials, different pasteurization modes are used.
There are long (at a temperature of 63-65 °C for 30-60 minutes), short (at a temperature of 85-90 °C for 0.5-1 minutes) and flash pasteurization (at a temperature of 98 °C for several seconds) .
Although such milk retains most of the beneficial components, it is not completely free from microbes, so it sours quickly.
Pasteurization does not completely protect against germs and harmful bacteria - while getting rid of some, it only makes others (spores) less active.
Therefore, pasteurized milk does not last long - even if sealed and refrigerated, it can only be stored for a few days. At room temperature, its life is reduced to several hours.
Ultrapasteurization of milk
Ultrapasteurization (from the Latin ultra - over, excessively, and pasteurization) is a heat treatment process to extend the shelf life of a food product.
This type of processing allows us to produce high-quality drinking milk that does not need to be boiled.
And boiled milk loses many of its healing properties. During boiling, proteins decompose and heat-sensitive vitamin C is destroyed. Calcium and phosphorus turn into insoluble compounds that are not absorbed by the human body.
Raw milk and fruit juices are usually ultra-pasteurized.
The liquid is heated for 2-3 seconds to a temperature of 135-150 °C and immediately cooled to 4-5 °C.
In this case, pathogens and microorganisms are completely destroyed.
Milk after this treatment is stored for 6 weeks or longer at room temperature.
In this way, microflora and bacterial spores are removed from the milk, which lead to sour milk, and the natural beneficial properties are preserved with minimal losses.
After processing, milk is packaged under sterile conditions in a sealed multilayer bag - tetrapack.
High-quality raw materials, plus instant processing and reliable packaging - this milk does not require boiling.
The process of ultrapasteurization of milk occurs in a closed system; there are special installations. Its duration is about 2 seconds.
Two methods of ultra-pasteurization are used:
- contact of liquid with a heated surface at a temperature of 125-140 °C
- direct mixing of sterile steam at temperatures from 135-140 °C
In English-language literature, this pasteurization method is called UHT - Ultra-high temperature processing; in Russian-language literature, the term “aseptic pasteurization” is used.
There are also other pasteurization methods, for example, in relation to milk - ULT (Ultra Long Time).
Ultra-pasteurization allows you to obtain milk that is completely free not only from microbes, but also from their spores and vegetative forms.
UHT milk remains fresh only in hermetically sealed, aseptic packaging.
After opening the package, milk should be stored in the refrigerator for no more than 4-5 days, otherwise it will spoil, like any other.
But milk, which initially contains no bacteria, does not sour as obviously as happens with ordinary milk, contaminated with a large number of microorganisms.
Such milk simply goes rancid after a while. Many people noticed this. This is not a sign of low-quality milk or a product loaded with preservatives. That's how it should be.
There is an opinion that you cannot get homemade yogurt or cottage cheese from UHT drinking milk.
In fact, this is not true. UHT milk does not have its own microflora, including lactic acid bacteria, so it needs help in the form of a starter.
For yoghurts, a bacterial starter is used, which contains Bulgarian bacillus and thermophilic streptococcus. For example, .
Unlike the usual and familiar pasteurization, after which some heat-resistant bacteria and their spores still remain in the milk, ultra-pasteurization (UHT) occurs at a higher temperature - 135-137 ° C, which allows you to destroy the bacteria completely, but all the beneficial substances in milk are preserved because the processing lasts only 2-4 seconds.
This is especially important, because under these conditions milk sugar (lactose) is not destroyed, and mineral salts (calcium, for example), vitamins and valuable enzymes retain their properties.
Now ultra-pasteurization (UHT technology) is the most advanced and popular milk processing technique in the world.
The US Institute of Food Technology in 1989 called this system "the greatest achievement of food technology of the 20th century." In France, Germany, Belgium, Spain and some other countries, this milk accounts for up to 90% of the total volume of product consumed.
UHT milk (ultra-pasteurized) is a high-quality product that, thanks to science and unique heat treatment technology, is not inferior in quality to fresh milk, retaining for a long time all the beneficial substances a person needs.
Sterilization of milk
Sterilization is complete freedom from all types of microorganisms, including bacteria and their spores, fungi, virions, as well as prion protein.
It is carried out by thermal, chemical, radiation, filtration methods. Here we are talking about sterilization in general - devices and tools, etc.
During sterilization, milk is kept at temperatures above 100°C for 20-30 minutes.
Such milk is completely sterile and has a long shelf life, but loses a significant part of its beneficial components.
Ultra-pasteurization is much more advantageous.
Heat treatment or pasteurization is the process of heating milk from 63 ºС to a temperature close to the boiling point.
This process got its name from the famous French scientist Louis Pasteur (1822-1892), who first used this method to destroy microorganisms in wine and beer.
The effect of pasteurization on microorganisms contained in milk depends on the temperature to which the milk is heated and the duration of exposure at this temperature.
Pasteurization destroys microbes, and sterilization (heating milk above boiling point) also destroys spores. Boiling destroys all microflora of milk, with the exception of spores that are resistant to boiling temperatures. Pasteurization without noticeable changes in the organoleptic properties of milk (taste, smell and consistency) destroys tuberculosis, brucellosis and other pathogenic bacteria.
In ordinary collected milk, 99% of bacteria die only under the condition of good, reliable sterilization of equipment, equipment, and utensils used in the pasteurization process. Thus, the addition of contaminated milk containing 1 billion bacteria to pasteurized milk (i.e., the amount that could remain inadvertently in dairy equipment) will increase the number of bacteria in milk to 1 million in 1 ml. These bacteria will actively multiply and will inevitably lead to spoilage of all milk.
Pasteurization, therefore, is the simplest and cheapest way to decontaminate milk.
Milk is also pasteurized during the production of all dairy products in order to protect them subsequently from undesirable processes that are caused by the activity of bacteria and especially E. coli, butyric acid bacteria, etc.
When cattle are kept on pasture, the microflora of milk is destroyed by heating more completely than when kept in stalls. This is explained by the fact that when kept in stalls, bacteria enter the milk mainly from manure particles. These bacteria are more resistant to heat due to their properties. When kept on pasture, milk contains mainly bacteria that multiply on plants. Before pasteurization, thorough cleaning of milk is necessary. In practice, three pasteurization modes are used:
during long-term pasteurization, milk is heated to 63-65 º C and maintained at this temperature for 30 minutes;
short-term pasteurization is carried out at 72-75 º C with holding for 15-20 s, which is carried out in a stream;
flash pasteurization - heating milk to a temperature of 85-90 C without holding.
Thermal effects on milk lead to some changes in its constituent substances. When heated, the gases dissolved in it evaporate from milk. Due to the removal of carbon dioxide, the acidity of milk decreases by 0.5-1 ºT.
At temperatures above 85°, casein partially changes. But milk albumin is most affected: at 60-65 °C it begins to denature.
The salt composition of milk is also disrupted during pasteurization. Soluble phosphate salts become insoluble. Due to the partial coagulation of proteins and the formation of insoluble salts, a milky sediment (burnt) is deposited on the surface of heating devices (pasteurizers).
Pasteurized milk is curdled more slowly by rennet. This is explained by the precipitation of calcium salts. Adding a calcium chloride solution to such milk restores its ability to coagulate.
Vitamins are resistant to high temperatures, especially if milk is heated without access to oxygen. Heating to high temperatures (80-85°) gives milk a special taste and aroma, which intensifies as the temperature rises. When boiling, the composition of milk also changes. For example, the content of vitamins A and C is reduced by almost 2 times. Nutrients ranging from 15 to 20 are lost due to the formation of sediments of proteins, fat and calcium salts on the walls of the dishes. Therefore, there is no special need to boil pasteurized milk.
At home, we can also recommend long-term pasteurization of milk, which can be done without much difficulty. It is produced through heated water. The milk poured into the pan is stirred with a clean spoon while heating. As soon as the temperature rises to 63-65 °C, heating should be stopped and maintained for 20-30 minutes. After this, place the pan with milk in cold water.
