What is pasteurization? Pasteurization of milk. How is milk pasteurized? Short-term pasteurization of milk is carried out at a temperature
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.
Pasteurized milk can be stored longer without losing its beneficial properties. Today, there are two different processes aimed at increasing the shelf life of dairy products: pasteurization and ultra-pasteurization. The processes are similar, but also have differences. You can pasteurize milk using a special bath, a regular or infrared pasteurizer.
History of pasteurization
French microbiologist Louis Pasteur is the founder of the pasteurization process. In the mid-eighties of the nineteenth century, winemakers turned to a famous scientist with a request to find a remedy that could cleanse wine of harmful and destructive enzymes. The result of a number of experiments was the discovery that you can get rid of harmful microorganisms by heating the wine to a temperature of 55 - 60 degrees. He applied a similar method to milk to clear it of the tuberculosis bacillus.
Pasteurization has taken root and become popular in many countries around the world. It began to be used not only for disinfection, but also to increase the shelf life of dairy products.
Types of pasteurization
Today pasteurization is divided into three types:
- Long-term (30-60 minutes, at a temperature of 64 degrees),
- Short (30-60 seconds, at a temperature of 86 -91 degrees),
- Instant (a few seconds, at a temperature of 98 degrees).
Pasteurization should be distinguished from sterilization. For sterilization, milk is brought to a temperature of 150 degrees and processed for half an hour.
Such long-term heat treatment leads to the death of all microorganisms, and the shelf life of the sterilized product reaches up to a year. The absence of lactic bacteria in it leads to the fact that the milk does not sour, but begins to taste bitter. The disadvantage of sterilization is that the product loses its nutritional value.
Pasteurization efficiency
Pasteurization of milk involves heating the product once for a certain time and to a certain temperature (depending on the type of pasteurization). The pasteurization process leads to the death of mesophilic bacteria, but lactic acid streptococci and enterococci retain their activity. During subsequent storage of milk at temperatures below +8 degrees, the bacteria reduce biological activity and do not impair the quality of the product.
Pasteurization of milk does not lead to the destruction of lactic acid rods - they stop developing only if storage conditions are properly observed.
Psychrotrophic bacteria are less resistant to the pasteurization process, so only a small number of microorganisms are retained in the finished product.
The efficiency of the process directly depends on the types and number of microorganisms contained in the original product. And storage conditions largely determine the effectiveness of pasteurization. If after milking the milk is immediately cooled to +3 degrees, then only psychrotrophic microorganisms survive and continue to multiply in it. They have fairly low heat resistance, so the pasteurization efficiency of such milk is 99.9%.
The development of psychrotrophs in a raw product leads to the production of heat-resistant proteases and lipases, which can impair the taste of not only pasteurized milk, but also of any dairy product.
Storing milk at temperatures above +9 degrees leads to the active proliferation of heat-resistant bacteria. The amount of their biomass can amount to more than half of all microorganisms found in milk. The pasteurization efficiency of such milk may be less than 97%.
Ultra pasteurization
This process is also a heat treatment of a dairy product to increase its shelf life. UHT milk can be drunk unboiled, and this is a definite advantage over its pasteurized counterpart. The boiling process leads to the destruction of all beneficial qualities, as well as the decomposition of proteins and a change in the absorption of calcium.
For ultra-pasteurization, special closed containers are used. The essence of the process is that the milk is brought to a temperature of 133-153 degrees, this temperature is maintained for two to three seconds, and gradually cooled to 4-5 degrees. This type of treatment leads to the death of all microorganisms.
Ultra-pasteurized milk does not sour, but retains all its beneficial qualities, since the heat treatment process does not negatively affect the state of vitamins, main lactic enzymes and mineral salts.
UHT milk can be stored for up to two months in a closed package, even without a refrigerator, at a maximum room temperature of +25 degrees.
An open box can be stored for no more than five days. After five days, UHT milk begins to taste bitter and acquire an unpleasant odor.
Modern technologies make it possible to produce ultra-pasteurized milk, which is not inferior in its beneficial qualities to whole fresh milk.
Milk pasteurizer
A pasteurizer is equipment designed for heat treatment of a dairy product. There are a number of requirements for pasteurizers:
- They must destroy all pathogenic bacteria,
- Ability to process a variety of products
- Preserve the unique qualities of processed products,
- Avoid product loss during processing,
- Be made from materials approved for use in the food industry.
Pasteurizers are divided into several types according to their main characteristics. So, according to their design, they are divided into open and closed. And depending on the work process, they can be periodic or continuous. In the dairy industry, continuous pasteurizers are more commonly used, but for the production of any canned products, a batch pasteurizer is more often used.
Another difference is the type of heat treatment. Some pasteurizers use sterile steam in the process. This method involves subsequent cooling of the milk in a special vacuum chamber. Others use a heat exchanger. The built-in regeneration department of which provides for a cooling process.
The usual package of a pasteurizer includes:
- Working capacity,
- Milk and water pumps,
- heating system,
- Pipelines,
- Remote Control.
Plate pasteurizers are more popular. They are able not only to quickly heat a dairy product, but also to maintain it for the required amount of time at a certain temperature and then cool it. The plate pasteurizer consists of:
- pasteurization column,
- Plate heat exchanger with cooling device,
- Centrifugal pump,
- Pipeline,
- Control systems.
- Long-term pasteurization bath
This device is capable of heating the product up to 95 degrees. A typical long-term pasteurization bath set consists of:
- double-walled bathtub with built-in electric heaters,
- control unit,
- motor,
- drain tap,
- pipe for pouring milk.
This type of pasteurizer is available in several versions, capable of holding from 60 to 2100 liters at a time. The average weight of a pasteurizer is 75 kg, and the weight of a device for pasteurization of 1000 liters is 340 kg.
Infrared pasteurizers
Infrared pasteurizers are used in a variety of fields. They are used to pasteurize milk from cows with mastitis. This dairy product is not suitable for humans, but is well suited for feeding calves. Another area of application is increasing the shelf life of bottled milk. Infrared pasteurizers are divided into three groups:
- Capacity up to 300 liters per hour,
- Capacity from 500 to 1500 liters,
- Capacity from 2000 to 500 liters.
Mini pasteurizers
Mini pasteurizers are available for home use. They are designed for milk volumes from 15 to 200 liters, the maximum heating temperature inside the device is 92 degrees. Typically, home pasteurizers come in the shape of a cylinder with a handle. Pasteurized homemade milk can be stored for up to ten days.
The weight of the device depends on the internal volume. The minimum weight of a pasteurizer designed for 15 liters is six kilograms.
People constantly strive to learn how to extend the life of products, but at the same time technologies are being developed that do not in any way affect the beneficial properties. Pasteurization technology was discovered in the 19th century by a man named Louis Pasteur. It was he who became the founder of immunology and discovered the possibilities of heat treatment of products, which can significantly increase their shelf life.
What it is?
You can often find milk and other products on store shelves that indicate that they are pasteurized. In fact, such a complex word just means that the milk was processed at high temperature, that is, it was heated, but not boiled, because then it would lose its beneficial properties. It is enough to heat it to 60 degrees and hold it at this temperature for half an hour to destroy pathogenic bacteria. If the temperature reaches 80 degrees, then 20 minutes is enough.
This time is enough for some of the bacteria to die, and the other part to reduce activity.
The pasteurization process has a beneficial effect on the shelf life of the drink, regardless of whether it was produced on an industrial scale or purchased on a farm.
Many young housewives do not know whether it is possible to pasteurize a product at home and what is needed for this. Indeed, pasteurization of milk at home is possible. They use not only a gas stove, but also an oven; you can even pasteurize it in a slow cooker.
If you buy milk in a tetra pack, then it is recommended to heat it not in a saucepan, but to place the package in a container with heated water. In fact, the pasteurization process will be the same, only the beneficial properties will be better preserved and the drink will undergo fewer changes. The process is carried out once, which is enough to protect yourself. Milk will not become better if it is constantly boiled, but the beneficial properties will become less and less each time.
As a useful tip, it is recommended to cool the fresh milk immediately, otherwise it will turn sour in a few hours at its own temperature. It is best to keep milk in the refrigerator in glass containers. But storing the drink in metal and plastic containers is not recommended, since the materials can react with the liquid and impart negative qualities to it.
Using a multicooker
There is only one way to properly prepare pasteurized milk in a slow cooker, and this is due to the properties of household appliances. When the equipment appeared in the kitchen of the modern housewife, it made many processes easier. Stews, grains, and more are cooked wonderfully inside. You can also easily pasteurize milk in it without having to stand at the stove and watch for it to escape. Moreover, it is not time that plays a decisive role, but temperature during the heat treatment process, therefore it is not easy to regulate the degree of heating.
With a multicooker, everything is easy: the appliance has a mode, all the housewife needs to do is set it and press a button. If you are processing homemade milk, just set it to 80 degrees and set the timer for 20 minutes. New multicookers have an additional mode, which is called “pasteurization”. You just need to pour the milk into the container, put it inside and press the appropriate button.
Kinds
In order for the drink to be well stored even in its processed form, the container into which it is then poured for storage must also undergo heat treatment. It is best to use glass jars that have a tight lid.
There are several types of pasteurization depending on the temperature at which it is carried out:
- long-term;
- ultra-high temperature;
- short-term high temperature.
The thirty-minute heat treatment process is called long-term pasteurization. At the same time, the temperature remains at 60 degrees. In terms of destroying microorganisms, this is the most time-consuming but also effective method.
It is impossible to carry out high-temperature short-term treatment at home; this type of pasteurization is typical for industrial facilities. The procedure requires special equipment that can heat milk and cool it in a few minutes. One of the significant disadvantages of this type of processing is accuracy: if you do not hold milk for a few seconds, the microorganisms will not die, but if you hold it too long, it will lose all its beneficial properties.
This is one of the reasons why pasteurized milk differs in quality at different enterprises. Even different batches of a drink from the same plant may differ in their properties.
As for instant heating, it was originally invented for mothers who are sick with HIV, and therefore cannot feed their children breast milk. The method is available for use at home, but to implement it you will need to organize a water bath. For pasteurization you will need 2 containers: one large and the other smaller. Water is poured into the first and put on fire, the second with milk is placed on water. As soon as the first pan begins to boil, you can remove the milk from the heat.
Will there be any benefit?
There are many opponents of the process of heat treatment of milk, who believe that the moment it is heated, it loses its beneficial properties and becomes useless for the human body. They argue that pasteurizing a drink is necessary only to increase its shelf life and nothing more. Due to ignorance of many nuances, they, without knowing it, talk about sterilization when the temperature of the milk reaches 100 degrees. Only in this case does the destruction of useful compounds occur, but not during the pasteurization process, when the maximum temperature reaches 80 degrees.
The method allows you not only to increase the shelf life of the product, but also to protect yourself, which is important when milk from a farm is consumed as food.
You will learn more about how milk is pasteurized in the following video.
Pasteurization of milk is a technology for disinfecting milk and extending its shelf life, which consists of heating the liquid once at a certain temperature for a certain time.
This technology is already more than one and a half hundred years old - it was first used in the middle of the 19th century by a microbiologist from France named Louis Pasteur. Actually, the name of the technology came from his last name.
There are various milk pasteurization modes- from long-term pasteurization (lasts 30-40 minutes at a temperature of 60 to 80 degrees) to instant (a few seconds at a temperature of 98 degrees). There is also ultra-pasteurization - it takes place at a temperature of more than 100 degrees.
Of all the pasteurization modes in home cheese making, long-term pasteurization is most often used (more on it below).
Why is pasteurization needed in cheese making? Can I use already pasteurized store-bought milk?
Choosing milk for cheese making is a double-edged sword. If you bought store-bought milk, it is already pasteurized, but the chance of getting cheese is 50/50. That is, it will either work out or not. And it is likely that with pasteurized store-bought milk you will have to use all sorts of tricks, such as adding calcium chloride, so that you still get cheese.
Fresh farm unpasteurized milk, in turn, almost always gives a guaranteed result - with good ingredients and adherence to the recipe, the cheese is almost excellent.
But unpasteurized milk may harbor certain threats in the form of unfriendly bacteria. Therefore, such milk almost always requires pasteurization. And even the presence of veterinary documents for milk and the presence of a “verified” farmer does not guarantee you the absence of unwanted microbes.
Therefore, our advice is this: it is still better to pasteurize farm milk in order to prevent the development of pathogenic microflora in your cheese.
Technology for pasteurizing milk at home
To pasteurize milk at home, you will need the following equipment:
- Pan with lid
- slotted spoon or large wooden spoon/spatula
And you need to be patient.
- So, pour fresh milk into a saucepan, place it on medium heat and, stirring continuously, heat to 72-74 degrees (use a thermometer). Some sources say it should be heated to 82, but that's playing it safe (see chart further down the page).
- Once the milk has reached the desired temperature, close it with a lid and let it sit for 30 seconds.
- After 30 seconds, place the pan in a container of cold water (you can use a large sink or bathtub). Here you quickly cool it to the temperature required according to the recipe (from 22 to 38 degrees, depending on the type of cheese).
All! The milk is pasteurized. After this, you can proceed directly to cheese making.
According to this source, the use of a temperature at which tuberculosis bacteria are destroyed makes it possible to eliminate other bacteria that are found in milk and are often pathogenic. If the specified milk pasteurization regime is observed, up to 99% of the milk microflora perishes, not excluding mammacoca and E. coli, which are harmful to cheese making.
By the way! Milk is not suitable for cheese making within two hours after milking! (it contains natural inhibitors that prevent the development of lactic acid bacteria). So if the milk is literally fresh, then you need to wait a couple of hours. Read more about the suitability of milk for cheese making.
Also a very important point : after pasteurization, milk becomes less suitable for cheese, because Calcium ions are released from the milk. And for coagulation (rennet coagulation) of milk, calcium ions are necessary. To compensate for their deficiency, after pasteurization of milk when preparing cheese, add to milk
Pasteurized milk is what stores offer us. It sells and is very popular. What is the difference between pasteurized milk and regular milk? And does she exist?
What is "pasteurization"?
Pasteurization is the process of heat treatment of liquids at a temperature of 60°C for an hour or 70-80°C for about 30 minutes. Why is milk pasteurized? The fact is that fresh milk contains not only beneficial but also harmful bacteria. During pasteurization, they are neutralized, as a result of which pasteurized milk is stored much longer than usual.The heat treatment used to perform the pasteurization procedure was popular back in the nineteenth century. Now this process has undergone significant changes. First, the milk is heated to the required temperature (depending on time), after which the product itself is cooled in special packaging, which, of course, is sterilized.
Pasteurization of milk allows you to keep the product fresh for almost three days (60 hours). You can also make yoghurts and so on from it. Sometimes milk goes through an ultra-pasteurization process. With this procedure, the liquid is heated to 135-150°C within a couple of seconds and instantly cooled to 4-5°C. After this, the milk has a shelf life of two months.
How to make pasteurized milk at home?
First you need to sterilize the container (glass jar) in which the milk will be stored. Sterilization takes no longer than twenty minutes. Then you can proceed directly to the pasteurization procedure.To do this, pour milk into the steamer (its top) and water down the bottom. It is necessary to heat the liquid to 63°C (you can’t do without a thermometer) and hold for half an hour, stirring. Next, lower the pan with milk into a container of cold water and wait until the temperature of the milk drops to 4°C. After this, pour the milk into a sterilized jar. Can be stored in the refrigerator for two weeks (no longer).
