The principle of sterilization is that within a certain temperature range, the lower the temperature, the slower the bacterial reproduction; The higher the temperature, the faster the reproduction. But if the temperature is too high, bacteria will die. Different bacteria have different suitable growth temperatures and heat and cold resistance abilities. Pasteurization is actually the process of using the characteristic of pathogens that are not very heat-resistant, and treating them with appropriate temperature and insulation time to completely kill them. But after pasteurization, a small amount of harmless or beneficial, heat-resistant bacteria or bacterial spores were still retained.
        The emergence of pasteurization originated from Pasteur's efforts to transform beer. At that time, the French brewing industry faced a headache, which was that beer would become sour after brewing and could not be consumed at all. And this kind of acidification phenomenon often occurs. Pasteur was invited to study this issue. After a long period of observation, he found that the culprit that makes beer sour is lactobacillus. Nutritious beer is simply a paradise for the growth of lactobacilli. Using a simple boiling method can kill lactobacilli, but in doing so, the beer will also be spoiled. Pasteur attempted to use different temperatures to kill lactobacilli without damaging the beer itself. Pasteur's research result is that heating beer at a temperature of 50-60 degrees Celsius for half an hour can kill lactobacilli and spores in the beer without boiling. This method saved the French wine industry. This sterilization method is also known as "pasteurization". Pasteurized milk should be stored at a temperature of around 4 ℃ and can only be stored for 3-10 days, at most 16 days.
  Sterilization methods: There are various types of pasteurization procedures used today. Low Temperature Long Term (LTLT) processing is an intermittent process that is now only used by small dairy factories to produce some cheese products. High Temperature Short Term (HTST) treatment is a "flow" process typically carried out in plate heat exchangers and is now widely used in the production of drinking milk. The products obtained through this method are not sterile, meaning they still contain microorganisms and require refrigeration during storage and processing. Rapid pasteurization is mainly used in the production of yogurt and dairy products. There are currently two commonly used pasteurization methods internationally:
One method is to heat the milk to 62-65 ℃ and maintain it for 30 minutes. By using this method, various growth pathogenic bacteria in milk can be killed, and the sterilization efficiency can reach 97.3%~99.9%. After disinfection, only some thermophilic bacteria, heat-resistant bacteria, and spores remain, but most of these bacteria are lactic acid bacteria. Lactic acid bacteria are not only harmless to humans but also beneficial to health.
The second method is to heat milk to 75-90 ℃ and keep it warm for 15-16 seconds, which results in shorter sterilization time and higher work efficiency. But the basic principle of sterilization is to kill the pathogenic bacteria, as too high a temperature can result in significant nutrient loss.
Development history: As early as 1935, Zander Hansen began manufacturing tunnel pasteurizers. Although it has undergone more than half a century of practice, today's Zan De Hansen is still a young, powerful, and innovative company.
This is precisely the result of Zand Hansen's continuous development of new sterilization technologies over the past decade. Meeting the demands of the external market while emphasizing the development of its own models has promoted the development of Zander Hansen sterilization machines. Today's pasteurization machines are like a leap forward, although only a few steps, they have already jumped out of the traditional structure. Here are a few development steps:
In 1989, a real-time pasteurization unit controlled by a personal computer.
1994: Centralized Heat Exchanger Supply System - Single Heat Exchanger Concept.
1997: Bottom trough pasteurizer - the new generation of Zander Hansen tunnel pasteurizer.
In the second half of 1996, a bottom slot sterilizer began assembly (officially put into operation in June 1997). It has pioneered a new structure for pasteurization machines, reducing the amount of water in the area to a low point. The equipped buffer system optimizes the configuration of cold and heat energy, and does not use valves.
The principle of the bottom trough sterilizer embodies the concept of a single heat exchanger and enables the centralized heat exchanger supply system to be fully utilized. This design is based on a modular structure that uses standard manufacturing methods and can also be adjusted to individual areas. This standardized and flexible feature is not only beneficial for Zand Hansen, but also for users, shortening the manufacturing, delivery, and installation time.
The bottom trough pasteurizer is the main model of the centralized heat exchange supply system and can fully demonstrate the excellent performance of pasteurization unit control - all theoretical indicators have been achieved here. Only when there are no other possibilities, should the purified water from the overflow system be used, which can reduce water consumption by 35% to 40% compared to traditional pasteurizers. The bottom trough pasteurizer uses an automatic filter belt instead of the traditional manual double screen, which not only enhances the strength of the machine but also simplifies its structure.
Practical application: It is a sterilization method for milk that can kill harmful pathogens to health and minimize changes in milk quality. That is to say, based on the principle of the difference between the heat death curve of tuberculosis bacteria with strong heat resistance and the heat damage curve of cream separation that is easily affected by heat in milk, a method of heating treatment is carried out for a long time at low temperature or a short time at high temperature. Among them, heating below 60 ℃ for 30 minutes has long been widely adopted as the standard for low-temperature sterilization worldwide. By using high-temperature treatment, although it may have some impact on the quality of milk, it can enhance the sterilization effect. This method is called high-temperature sterilization, which means heating above 95 ℃ for 20 minutes. The pasteurization method can also be applied to fermented products in addition to milk.
Usually, bagged milk sold in the market is produced using the pasteurization method. The factory collects fresh milk, processes it at low temperatures, and then sterilizes it using pasteurization. Bagged milk produced using this method can usually be stored for a longer period of time. Of course, the specific processing and techniques are much more complex, but that's the overall principle.
It should be pointed out that drinking fresh milk (referring to freshly squeezed milk) is actually unsafe because it may contain harmful bacteria to our body. Another point is that pasteurization is not omnipotent, and milk treated with pasteurization still needs to be stored at a lower temperature (generally<4 ℃), otherwise there is still a possibility of spoilage. Therefore, many methods of selling bagged milk in the market are very non-standard.
Pasteurized milk is the most commonly consumed milk variety in the world. In countries such as the UK, Australia, the US, and Canada, the consumption of pasteurized milk accounts for over 80% of liquid milk. The varieties include fully skimmed, semi skimmed, or full fat. In the US market, almost all of it is actually pasteurized milk, and it comes in large packages (1 liter, 2 liters, 1 gallon). Citizens can buy enough fresh milk to drink for a week at supermarkets once. There are few sterilized pure milk products sold in the market, and some small towns simply cannot buy them.
Pasteurized pure fresh milk preserves the nutrition and natural flavor of milk well, making it a good choice among all milk varieties. In fact, as long as pasteurized milk is stored at a temperature of around 4 ℃, the reproduction of bacteria is very slow, and the nutrition and flavor of milk can remain unchanged for a few days.
At present, pasteurization machines are mainly used for commercial purposes in the market, and pasteurization is also an internationally recognized sterilization standard used by many large enterprises. Pure milk and other flavors of yogurt on the market are now pasteurized. With the development of green and healthy food, pasteurization machines are now used in many small dairy farms. Small dairy farms use 100 or 200 liters, mainly to produce fresh pure milk and distribute it to the market. The current pasteurizer is equipped with a cold water circulation system, and there are usually two types of refrigeration methods. One is compressor refrigeration, which is fast and effective. The other is cold water circulation refrigeration, which mainly uses logistics cooling to reduce costs.
Process flow: The pasteurizer is a curve that converts the PU value set by the temperature controller into the actual control temperature of each temperature zone water tank, and accurately controls the temperature changes in each temperature zone through temperature detection. The main drive motor drives the bottle conveying chain network of the upper and lower layers to preheat the material through three temperature zones, sterilize it in two temperature zones, and cool it down in three temperature zones.