Humanity has always tried to be able to correctly extend the period of use of products without reducing its beneficial properties. In the mid-19th century, the great scientist, founder of immunology, Louis Pasteur, discovered the technology of pasteurization, which made it possible to disinfect food products and significantly increase their shelf life.
In the modern world, most liquid products undergo this process. We most often see the word “pasteurized” on milk packaging in stores. And it becomes interesting, is it possible to pasteurize milk at home? Absolutely yes. So let's try to understand this process in detail.
What is milk pasteurization?
Milk pasteurization 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 mid-19th century by a microbiologist from France named Louis Pasteur. Actually, the name of the technology came from his last name.
There are various modes of pasteurization of milk - 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.
Meaning
The advantages of pasteurization are obvious:
- accessible method;
- not expensive;
- the shelf life of the product increases;
- the environment is disinfected;
- the beneficial properties of the substance are preserved.
People who consume this milk are completely protected from intestinal disorders.
Sterilization
Sterilization is the process of processing milk at temperatures above 100 °C, at which all microorganisms, their spores and enzymes are destroyed.
There are 2 types of it used in production:
- 115-120 °C for 20 minutes;
- 140-150 °C for 2 seconds.
Simply put, sterilizing milk is boiling it.
Unlike pasteurization, it takes place at very high temperatures. The process affects the chemical and organoleptic properties of milk, its taste.
What is pasteurized milk?
This is a heat-treated product. It increases shelf life. In the process of industrial pasteurization, milk is heated to 60 degrees for 1 hour or to 80 degrees for half an hour. Under the influence of this temperature, all pathogenic bacteria and microbes that are always present in whole milk are destroyed. During pasteurization, up to 90 or even 99% of microorganisms die (data on this issue vary). Using pumps, milk is cleaned of foreign impurities, then pumped into a separator, where the cream is separated. Then the product is cooled and placed in a special container, packaged and sent to the refrigerator.
The shelf life of the product ultimately increases to a week if stored in a sealed container in the refrigerator. Then the milk sours and curdled milk is formed. At room temperature the product can be stored for only a few hours.
Composition and calorie content
Not a single GOST precisely regulates BZHU and other features of the composition of pasteurized milk - the main thing is that it corresponds to what is indicated on the packaging. Even for fresh milk, these indicators can vary significantly, so it is not surprising that indicators vary markedly between different manufacturers. For this reason, our indicators will only be approximate, and the consumer is obliged to double-check the information by reading the exact content of the substances he needs on a specific package.
Most types of pasteurized milk have the least protein - its amount is in the range of 2.5-3%. On the contrary, carbohydrates are present in the composition the most - 4.5-5.5%, with the most popular value being 4.7%. As for fat content, this component is the most variable, because, as mentioned above, many manufacturers even regulate it artificially - it can fluctuate between 1-6%. Useful components in the form of microelements and vitamins in all types of milk are approximately the same, there is especially a lot of calcium and iodine, copper and strontium, as well as vitamins B and D.
If we talk about the calorie content of a natural drink, then it largely depends on the balance of BJU, especially on the amount of fat. As a result, the energy value can range from a very modest 44 kcal to a much more serious 71 kcal, so those who strictly monitor the calorie content of the foods they eat should be on their guard.
What is the difference between UHT milk?
Recently, on store shelves you can find not only pasteurized milk, but also ultra-pasteurized milk. It is produced using a similar technology, but heats up to a higher temperature of 135 degrees in just 2-3 seconds. The conducted studies confirm that such a short processing time is sufficient for high-quality purification of milk from harmful bacteria. Then it is immediately cooled to +4 degrees.
Ultra-pasteurization extends the shelf life of the product to 6 weeks or more, even when stored at room temperature. After opening the package, it remains fresh for 3-4 days, then it sours, like all other milk.
What is healthier - pasteurized or sterilized milk?
Sterilization occurs at a much higher temperature - up to 150 degrees. Thus, the raw materials are processed within half an hour.
There are 3 main differences between the two types of product:
- Pasteurized milk retains beneficial lactic acid bacteria, while sterilized milk does not contain any beneficial microflora.
- Pasteurized milk can be stored in a hermetically sealed box for about a week (ultra-pasteurized milk - 2 months or more). Sterilized products do not lose their quality for a year after production, if the original packaging is not opened during this time.
- Sterilized milk has less nutritional value than pasteurized milk.
In terms of practicality, sterilized milk wins. It lasts much longer. In terms of composition, a pasteurized product is still healthier.
How long is it stored?
Fresh milk has a very short shelf life, so many consumers sincerely hope that the pasteurized version, which they perceive almost as preservation, will last much longer. Such people will have to be disappointed, because regular pasteurized milk, when sealed, is usually stored for no longer than 3-4 days, and when unsealed it is advised to consume it within 24 hours.
Moreover, even such a short period requires storage conditions in the refrigerator, whereas at elevated temperatures, ripening can occur much faster.
You can slightly extend the life of the product by pouring it into sealed consumer containers or boiling it. In the first case, lactic acid bacteria can “start up” in the liquid even at the time of transfusion, and in the second, the product must be boiled in advance before it has deteriorated and such an operation does not negatively affect the usefulness of the milk.
With UHT milk the situation is radically different - it heats up much more, so there is absolutely no “life” left in it. Thanks to this, such a drink is optimal for delivery over any distance, and even more so it can be stored in the refrigerator. In warehouses and other specialized places, such a drink can be stored for several months, although it should be clarified that in an open package, the rapid formation of a colony of lactic acid bacteria is still possible.
At the same time, you need to understand that the expiration date is an abstract value if you do not know the release date. Ordinary pasteurized milk is a perishable product, so this point must be clarified - the date must be indicated on the packaging in a visible place. By the same expiration date, you can also determine how healthy the drink is, because from all of the above it follows that a truly natural and healthy product cannot be stored for a long time
Nutrient Analysis Results
| Instant heating | Low temperature pasteurization (according to Holder) | No heating | |
| Vitamin B 12 (pg/ml) | 862.8 (667.0) | 862.3 (651.1) | 724.5 (488.0) |
| Vitamin C(mg/dl) | 4.2 (2.5) | 3.6 (2.2) | 5.3 (1.6) |
| Vitamin E (mg/l) | 2.7 (2.0) | 2.4 (1.3) | 3.0 (1.2) |
| Pyridoxal phosphate (µg/l) (n=5) | 29.0 (17.2) | 28.0 (17.4) | 28.8 (17.3) |
| Folic acid (ng/ml) (n=5) | 18.7* (3.8) | 19.0* (1.5) | 13.3 (1.2) |
| Riboflavin (µg/l) (n=5) | 728.0 (1142.9) | 704.4 (1094.5) | 667.2 (955) |
| Thiamine (nmol/l) (n=4) | 18.0 (9.1) | 17.8 (6.8) | 12.3 (4.6) |
| Lactoferrin concentration (ELISA, mg/ml) (n=10) | 0.214* (.272) | 0.826* (.246) | 1.341 (0.154) |
| Lactoferrin digestible (% absorption) (n=9) | 84 (10.1) | 80.3 (8.8) | 87.7 (12.5) |
| Lysozyme digestible (% absorption) (n=9) | 70.6 (21.0) | 75.8 (14.9) | 89.0 (14.1) |
(*p <0.05, compared to samples without heating)
Features of the method
Pasteurization of milk involves heat treatment of the drink. The heating process occurs up to 63-100 degrees Celsius (the exact temperature indicator is determined by the chosen method). The heat treatment method is named after the scientist Louis Pasteur from France, who was able to apply the technique to eliminate microorganisms in liquid. The effectiveness of pasteurization is determined by the temperature and duration of exposure of milk under a certain regime. Despite the lack of boiling, only pathogenic bacteria are eliminated. The optimal temperature regime of heat treatment preserves the beneficial milk microflora and the optimal characteristics of the drink (consistency, taste and smell).
To successfully destroy pathogenic bacteria, you will need to carry out the procedure correctly. Sterile containers and equipment must be used. If sterilization is carried out at an unsatisfactory level, there is a risk of up to one billion bacteria entering the drink with further active reproduction. As a result, the number of microbes will reach a million per milliliter.
Pasteurization is recognized as an effective and inexpensive way to disinfect the resulting drink for further fresh consumption or the preparation of dairy and fermented milk products.
The effect of pasteurization on the properties of milk
During pasteurization, profound changes in the physicochemical and biological properties of milk are not observed. The content of protein and vitamins does not change significantly. Organoleptic parameters such as smell, taste, color, consistency remain the same. Therefore, it is believed that the nutritional value of the product remains almost the same level.
However, as a result of heat treatment, some processes in milk still occur. The degree of changes in physicochemical characteristics depends mainly on the heating temperature and holding time. Heat denatures milk proteins. The most sensitive are serum ones, for which it is enough to exceed the threshold of 65 °C. Casein has higher stability. Vitamins are partially destroyed, especially those soluble in water, and enzymes are deactivated. Phosphorus and calcium salts pass from a soluble to an insoluble state and precipitate.
When planning pasteurization, it is necessary to choose a method so that changes in the components of the product that affect its nutritional value are minimal.
Advantages and disadvantages
Pasteurization is a desirable process in production and at home. After heat treatment, the drink is stored in the refrigerator for a long time, retains all its beneficial properties and is absolutely safe for health. The only disadvantages include the time spent on its processing and the need to control the milk pasteurization temperature.
Benefit
For the last twenty years, there has been hysteria in the world about the fact that drinking milk is harmful. Thanks to doctors, nutritionists, and biologists, this drink is regaining lost ground, because it is considered a product given to us by nature for a balanced diet. The pasteurized drink is inferior in quality to the fresh one, but is also healthy.
Its advantages are unconditional:
- low calorie content;
- suitable for baby food;
- rich in milk protein;
- one glass contains almost ½ the daily requirement of calcium;
- the composition includes minerals such as iodine, copper, strontium;
- Vitamins B and group D are present.
This product can be used by those people for whom the taste of steam is unacceptable. Skim pasteurized milk is an excellent option for those who cannot tolerate animal fats.
Possible harm
Only consuming a low-quality product can lead to negative consequences. Some unscrupulous manufacturers add chemicals to extend its shelf life.
Another possible problem is that if stored improperly, pathogenic microorganisms can begin to multiply.
Pasteurization methods
There are 3 methods of pasteurization:
This method is called long-term pasteurization. Milk must be heated to a temperature of 63-65°C and pasteurized for half an hour;
This method, otherwise called short-term pasteurization, involves heating the product to a temperature of 72-75°C. After holding for 15-20 seconds, the heat treatment should be stopped; During flash pasteurization, milk should be brought to a temperature of 85-90°C without further holding.
Heat treatment (at 80-85°C) changes the taste and aroma of milk. When exposed to temperature, some elements contained in milk change their physical and chemical properties, and accordingly the composition of the product changes slightly.
For example, the gases contained in milk evaporate, the acidity of the product decreases slightly (by 0.5–1 °T), changes also affect the salt composition (phosphate salts become insoluble). Heating devices used in the production of pasteurized milk may become coated with burnt deposits caused by milkstone deposits. Calcium salts slow down the coagulation of milk, which requires the addition of an artificial solution of calcium chloride. When milk is processed using flash pasteurization (when the temperature is above 85°C), casein begins to change. And albumin protein tends to denature already at 60-65°C. Vitamins are the most resistant to heat treatment, especially when the access of oxygen to the pasteurizer is limited.
Experts do not recommend boiling pasteurized milk, as this changes the composition of the milk, reducing the content of nutrients and vitamins A and C. You can pasteurize milk at home in a water bath. When heating the water in a saucepan to 63-65°C, turn off the heat, let the milk stand for 20-30 minutes, and then cool it by placing it in cold water. During the heating process, it is necessary to constantly stir the milk.
Long-term
The most gentle method of processing milk. Pasteurization takes place automatically at enterprises. The equipment is equipped with an artificial intelligence program that does not fail. Maintenance personnel at dairy plants work around the clock, monitoring the entire technological process on monitors: heating temperature, degree of filling of tanks, time.
Treatment takes 30 minutes at 63-65 °C. During this time, all pathogenic microorganisms die, while lactic acid microorganisms remain.
Short term
This is high-temperature pasteurization - a kind of shock for the product. For 15-20 seconds the temperature in the tanks reaches 72-75 degrees.
Types of pasteurizers
According to the mode of action on the product, all units are divided into two groups: direct and indirect.
Among indirect ones, thermal ones are more common, in which milk is heated by intermediate coolants: hot liquid or air, steam, flue gases.
Other installations of this type are electrical. According to the method of heat transfer, they are either elemental or inductive.
Direct pasteurizers heat the product using ultraviolet or infrared radiation, as well as ultra-high frequencies. This also includes electrode and hydrodynamic devices.
The latter are divided into fluid friction devices, cavitation devices, and units in which both fluid friction and flow turbulence are used.
In addition, there are capacitive and flow-through pasteurizers. The former operate in a cyclical manner and are therefore ineffective. The second has a much smaller number of technological operations and their duration.
In industry, four types of pasteurizers are most often used: plate, tubular, steam with displacement drums and baths for long-term pasteurization.
The baths are designed to heat milk for 30 minutes. Temperature - 63 - 65 °C. Their main disadvantage, in addition to low productivity, is the possibility of microorganisms (thermophiles) multiplying in the product.
Therefore, all over the world they prefer units for short-term and flash pasteurization that heat the raw materials to a higher temperature - steam, tubular and plate.
For milk, the latter are considered the best, but with the help of tubular ones you can pasteurize viscous products. Steam and electric devices have low efficiency and problems with scale in boilers.
In direct-acting units, the heat source is the hydraulic resistance of the rotating fluid or electric current.
Among them, the most popular are installations in which milk is disinfected using ultraviolet radiation and pasteurized using infrared radiation (2.9 - 3.2 microns).
Microwave devices use waves with a frequency of more than 3000 MHz. The energy utilization factor reaches 0.8. The disadvantage is the complexity of the design. The efficiency of electrode heaters is up to 98%. However, they are not safe or reliable.
Effectiveness of disinfection
Pasteurization of milk is aimed at eliminating pathogenic microbes. To do this, the drink is heated once. It is mandatory to observe a certain temperature regime and focus on the holding time. Mesophilic bacteria die most quickly, but other microbes may remain active. If the liquid is stored at a temperature less than +8 degrees, it is possible to get rid of pathogenic microflora, the product becomes of high quality and useful. The development of remaining bacteria stops if the drink is stored properly.
The effectiveness of pasteurization depends on the microflora and composition of the drink being processed. For this reason, the initial quality of the product is taken into account. Subsequently, storage conditions determine the final effectiveness of disinfection. If timely cooling does not occur, microorganisms continue to develop. To increase the efficiency of heat treatment, it is recommended to cool the milk received after milking to +3 degrees to timely eliminate most bacteria. Violation of storage temperature activates the development of microflora, so pasteurization technology becomes less effective and it will be difficult to improve the microflora in the future.
To ensure a successful procedure, equipment and inventory are disinfected. If the preparation was unsatisfactory, the composition of the product will be worse due to the continued activity of bacteria. An increase in the content of enterococci in milk after pasteurization indicates unsuccessful heat treatment of the product, which remains dangerous.
Milk obtained through ultra-pasteurization can be stored without refrigeration at room temperature for up to 4 months.
Ultra pasteurization
A type of heat treatment, also called “asepsis” or higher pasteurization. This is a process in which milk is brought to high temperatures for 2 seconds and immediately cooled to 4-5 degrees. This shock therapy kills most harmful microorganisms, due to which the drink is stored for 6 months at room temperature.
Today, two methods of ultra-pasteurization are used in production, which will be described below.
Contact
Imagine a pipe within a pipe. The liquid product passes through the inner pipe, and water heated to 125-130 °C passes through the outer pipe. When milk comes into contact with a hot surface, it undergoes heat treatment. Disinfection of juice occurs in a similar way.
Direct mixing with steam
The system involves injecting sterile steam at 135-140 °C directly into the product, and then filling it into TetraPak packaging.
Ultrapasteurization is common in the USA and a number of European countries; it is considered economical because it reduces the energy consumption of refrigeration units. In France, Spain, and Italy, such processing accounts for 95% of milk. In our country, products with a long shelf life are treated more warily; the percentage of aseptic drinks on the market is still small.
Pasteurization in industry
Nowadays, for industrial heat treatment of products, TEK hydrodynamic units are used, which are also suitable for mixing, homogenization (breaking fat globules into smaller ones), emulsification (producing emulsions by separating the drop-liquid phase from supersaturated solutions, vapors). Manufacturers offer different models of equipment, so each enterprise can choose the most suitable option. It is assumed that it is possible to shut down the plant’s boiler room and organize the procedures at minimal cost.
Proper heat treatment in the dairy industry of a product eliminates pathogenic bacteria from the composition and improves taste characteristics. Clumps of high-molecular compounds are crushed by cavitation bubbles. At the same time, a reduction in energy costs is guaranteed.
Modern installations are configured taking into account what the pasteurization temperature should be and the further conduct of each stage and the exit of liquid from the installation. Careful process control increases the efficiency of the product heat treatment procedure. Modern pasteurizers (hydrodynamic units) heat liquid in volume. A new class of pasteurizers eliminates product burning.
In industry, pasteurizers with several sections (3, 4 or 5) are used. In this case, the main parameters of the installations are taken into account.
- The temperature of heat treatment and cooling must be set before the start of the procedure. This is required to effectively disinfect the product and eliminate all unwanted bacteria from the composition.
- Raw milk must enter the regeneration (recuperation) section for first processing. The optimal product temperature is 10-35 degrees.
- The separator is used to clean the incoming drink. In this case, heating occurs to 37-45 degrees (the initial indicator is taken into account).
- The hot water temperature is then set for pasteurization. The maximum permissible indicator is taken into account when carrying out pasteurization. In this case, the water should be hotter than milk.
- The next stage is cooling. It is recommended to take into account the time of year and local conditions to properly configure the equipment used. Usually milk should be colder than 9 degrees. For this, water (artesian, tap, ice) or brine can be used.
The pasteurizer, which is a plate heat exchanger, must be functional and reliable. The equipment must be configured taking into account how milk is pasteurized in production. This is required for careful control over the heat treatment of milk.
Final bacterial population (Metchnikoff number)
As a result of pasteurization, it is necessary to ensure that the microbial population is quantitatively reduced to a certain minimum level. This condition is expressed by the formula:
NK < Me
Here NK is a quantitative indicator of microbial biocenosis in milk following pasteurization; Me – Mechnikov number. It represents the minimum microbial population determined by economic and technological conditions. If this inequality is satisfied, then the milk flasks will contain a healthy and safe product.
Pasteurization of milk at home
Even though pasteurization seems like a complicated process, it can be done at home. So, how to pasteurize milk without special industrial installations? The process is carried out in several stages.
Pasteurization of milk at home
- Fresh milk is poured into a basin and the heat is turned on to maximum. The milk must be constantly stirred so that it heats evenly.
- When the milk reaches 72 degrees, turn off the heat and cover the pan with a lid. It should infuse for no more than 30 seconds.
- After this, the container with milk is transferred to a bowl of cold water and cooled to 22-38 degrees.
That's it, pasteurization is complete, and you can consume high-quality milk without bacteria.
The slow cooker can also be used for pasteurization. Modern models have a special “Pasteurization” mode. Milk is simply poured into the multicooker bowl and the “Pasteurization” mode is set. There is no need to control the process, the multicooker will do everything and at the end will notify you with a signal that the work has completed.
Interesting! Modern multicookers have a “Pasteurization” mode, which allows you to process the product at home without any difficulties.
Pasteurization is an effective process of disinfecting milk before its subsequent consumption or processing. It also allows the milk to be stored better. This processing technique is used for milk that is sold or consumed at home. If pasteurization is carried out correctly, the milk will remain healthy, but will not contain pathogenic microorganisms. This product is of high quality and pleasant taste, and most importantly, it is absolutely safe for consumption.
Pasteur criterion
To characterize the process, the average effect of pasteurization is used for a certain theoretical (that is, according to calculation, sufficient to destroy microbes) time z. If q is the actual heat treatment time, then this parameter is equal to q/z. This value is considered an indicator of completion. If q < z, then pasteurization has been partially carried out and the microbiological purity of the raw materials is not guaranteed. There will be too many bacteria in the milk cans When q = z, the process is completely completed. In the case q > z, the necessary results were also achieved, but the work was unnecessarily lengthy.
At the suggestion of G. A. Cook, the average effect of pasteurization was called the “Pasteur criterion”, with the designation Ra.
Since pasteurization is a long process, the value of Pa depends on how the temperature of the liquid changes over time. For example, in plate devices, the destruction of microbes occurs in the pasteurization section at a critical temperature. Then - in the holding tank. After this, partially, in the recovery or regeneration section. To determine the total (integral) effect for each section, the elementary effect of the process (dq/z) for an infinitesimal unit of time (dq) is calculated. Then the integral is taken according to the formula:
Ra = ʃ(dq/z)
Pasteurization is considered complete if the total Pasteur criterion for all sections of the unit is equal to or greater than one:
Σ Ra ≥ 1
How long does milk last after pasteurization?
We figured out what sterilized milk is. Now let's talk about the shelf life of a product that has undergone this heat treatment.
Fresh milk does not last as long as many of us would like. Therefore, when purchasing pasteurized milk, consumers sincerely believe that due to this heat treatment, the product is almost preserved at the factory, which means it is able to retain its beneficial properties and freshness for a long time. But, unfortunately, everything is not as cloudless as we wanted.
The shelf life of regular pasteurized milk in sealed form is no more than 4 days, and after opening the package it begins to sour within 24 hours. Let’s say more, even with such a short shelf life, the product should be kept in the refrigerator, because at room temperature it will lose its beneficial properties even faster and turn sour.
Advice! It is possible to extend the shelf life of pasteurized milk by pouring the product into an airtight glass container or by boiling it. In the first case, lactic acid bacteria can appear in the liquid even at the time of transfusion, and in the second, the product should be boiled in advance, before it becomes unusable, and such a procedure does not negatively affect the usefulness of the milk drink.
Speaking of ultra-pasteurization, the situation here is significantly different - milk is heated to critically high temperatures, which negates the existence of any viable microflora in it. Yes, milk no longer has beneficial properties, but its shelf life is already quite impressive, allowing it to be transported from the manufacturer to different points far removed from it, without fear for the preservation of the taste of the product.
In warehouses and other specialized places, UHT milk can be stored for several months. In open packaging, the shelf life is reduced, but, unlike a pasteurized product, we are not talking about several days, but about several weeks.
It’s worth understanding right away that if you don’t know the production date of a product, then the expiration date is an abstract value. Pasteurized milk is a perishable product, and therefore this aspect of the issue should be clarified - the release date and expiration date are indicated on the container.
Using the same shelf life, it is also possible to determine the benefits of the drink. So, from all of the above it follows that a truly natural and most healthy drink cannot be stored for a long time.
At what temperature is it advisable to store pasteurized milk? The standard temperature for refrigerators is 6-8°C. Under such conditions, the product is able to retain its beneficial properties throughout the storage period specified by the manufacturer.
How to choose healthy milk in the store?
There are many varieties of pasteurized milk . Therefore, in the store you should first look at the production date and expiration date. If it has expired or will expire soon, it is better to refuse the purchase.
Plastic bags are not suitable for long-term storage of the product. They are also not strong enough. Plastic transfers foreign taste and odor to milk. Glass bottles do not have this disadvantage, but it is better to choose products in cardboard bags. They are great for long-term storage.
You should also study the composition. If it says whole milk, it is a natural product that has been heat-treated. Whole milk can be diluted with reconstituted milk - made from dry powder. It is not necessarily of poor quality, there are simply fewer useful substances in such a product.
There is an easy way to check the quality of milk. You need to drop a drop of it into a glass of water. If it sinks to the bottom, the milk is whole; if it spreads, it is diluted.
Good pasteurized milk does not have sediment, but this can only be checked at home after opening the package.
Antibiotics are often found in imported milk. If it does not sour for a long time, it means that these substances are in the product, as well as acidity stabilizers. It is clearly not worth buying it - it will not bring any health benefits.
