UHT milk is a dairy product with a long shelf life that can be directly consumed. This dairy product not only improves the color and taste, but also improves the original nutritional value. Sterilized milk, also known as long-lasting fresh milk, refers to products that are using fresh milk as raw material, then after purified, standardized, homogenized, UHT sterilized and aseptically packed into containers.

UHT milk does not need to be refrigerated and can be stored at room temperature. Depending on the packaging container, the shelf life generally ranges from 3 months to 12 months.

The UHT milk processing equipment includes raw milk receiving and cooling system, raw milk standardization and prepasteurization system, milk UHT sterilizing system, UHT milk aseptic storage and filling system. The auxiliary equipment like CIP system, chill water generating system, boiler, and RO soft water treatment system are needed for the whole production line. All the machines are made of SUS304/316L material.

The capacity of the production line can be designed from 1 ton/hour to 50 tons/hour according to the different requirements of customers. 200g—2500g aseptic cartons, aseptic pouches or PE bottles can be packed according to the client’s different requirements.

Due to the strict hygiene requirements of UHT milk processing, the whole system are fully automatic and controlled by PLC and automatic pneumatic valves to avoid the risk of the second pollution. The whole system keeps milk processed in a closed environment to ensure the commercial aseptic state of the final product.

The UHT (Ultra High Temperature) milk production process typically involves raw milk reception, milk separation and standardizing, homogenization, heating to 135-150°C for 2-4 seconds, cooling, aseptic filling, and packaging.

UHT milk in bottles: The secondary sterilized milk usually will be filled into PE material bottles, and the shelf life is 6 months with normal temperature.

UHT milk in aseptic cartons: The most popular package for UHT milk is aseptic cartons, the aseptic cartons include diamond pack cartons, SIG Combibloc pack cartons, Tetra Pak aseptic brick cartons. These cartons are composed of 3-7 layers of paper, PE, and aluminum foil composite material, which has very good light resistance and airtightness and extend milk shelf life to 6-9 months stored with 20-25℃.

UHT milk in aseptic pouches: It mainly refers to Tetra pak aseptic pillow pouches and PrePack pouches. The shelf life of UHT milk in these aseptic pouches can also reach 45-60 days.

The raw milk undergoes acceptance, preliminary purification(if you want to make skimmed UHT milk, you can add one centrifuge separator to remove the fat in milk after purification),pre-pasteurization, and then cools to about 4℃, and stores it in a milk insulation tank. After standardization, homogenization, UHT sterilization and degassing, the end UHT milk will be filled into an aseptic carton or pouch packaging.

Secondary sterilization milk: the milk is pasteurized in advance, then filled into the container, and then sterilized by pressure in a retort sterilizer at 110-120°C for 10-20 minutes. This kind of sterilized milk is generally filled into plastic bottles or glass bottles. The product shelf life generally reaches 6 months.

Ultra-high temperature sterilized milk (UHT milk): raw cow (goat) milk is used as raw material, with or without reconstituted milk. In the state of continuous flow, it is generally sterilized at 120-150℃ holding for 0.5-4S. Through rising sterilizing temperature and shorten holding time can also achieve the same sterilization effect. This sterilization method is called ultra-high temperature sterilization. The UHT milk usually filled into aseptic cartons and pouches.

Sterilized pure milk (P≥2.9%): raw cow and goat milk or reconstituted milk as raw materials, skimmed or non-skimmed, ultra-high temperature instantaneous sterilization, and aseptic filled into cartons or pouches.

Sterilized flavored milk: (P≥2.3%): The protein content needs to be greater than or equal to 2.3%, and ingredients like fruit juice can be added to such dairy products.

The purpose of raw milk purification is to remove mechanical impurities in the milk and reduce the number of microorganisms. Filter purification or centrifugal purification can be used. Simple primary filtration is performed by installing a filter screen on the milk receiving tank and spreading multiple layers of gauze. The filter cloth should be cleaned and sterilized frequently. The use of a centrifugal milk purifier can significantly improve the purification effect and help improve the quality of the product. The centrifugal milk purifier can also remove breast somatic cells and certain microorganisms in the milk. The milk purifier is placed after filtering and before cooling.

Generally, If the capacity of UHT milk processing line is big, then there is necessary to pre-pasteurize. The purpose of pre-pasteurization is as follows:

1. Preliminarily kill most bacteria and pathogenic bacteria, make UHT sterilization more thorough, to ensure the safety of food and improve the storage of finished products.
2. Inhibit the activity of enzymes, so as to avoid fat hydrolysis, enzymatic browning and other undesirable phenomena in the finished product. The sterilization temperature is 80℃ and the time is holding for 15min.

The cooling temperature is 5°C to inhibit the growth of bacteria. The number of microorganisms in milk varies with the length of storage time and temperature. The plate heat exchanger is applied to cool down the milk.

In order to ensure the continuous production of the factory, there must be a certain amount of raw milk storage. Generally, more than two storage tanks are set up. The storage tanks are equipped with stirring to stir the raw milk regularly to prevent fat from rising and causing uneven distribution of raw materials.

Homogenizer is the mechanical treatment of the fat globules in the milk, so that the fat globules are uniformly distributed in the milk. Homogenization generally adopts two-stage homogenization. The material continuously passes through two homogenizing heads to open the sticky fat balls. The homogenization temperature is 55-65 degrees Celsius and the pressure is 20-25Mpa. This kind of homogenized milk quality and effect all reached good.

The ultra-high temperature instant sterilization machine is a core process of producing UHT milk, it means that the milk is heated to 130-150°C through a heat exchanger under the state of continuous flow, and kept at this temperature for 4-6S to achieve commercial sterility. Sterilized by this method, on the premise of effectively killing microorganisms, the nutrients in the milk are retained to a great extent, and the produced milk can be stored at room temperature for about 6 months to about a year.

Ultra-high temperature sterilization methods are divided into indirect and direct methods:

Indirect heating: The raw milk is preheated to 66℃ by the high-temperature sterilized milk in the previous stage in the plate or tube heat exchanger (while the high-temperature sterilized milk is cooled by the new milk), and then passes through a homogenizer at a pressure of 15-25mpa After homogenization, it enters the heating section of the heat exchanger, is heated by the hot water system to 137℃, enters the insulation pipe for 4S, and finally enters aseptic cooling, from 137℃ to 76℃, and finally enters the recovery stage. The fresh milk is cooled to 20°C, and finally enters aseptic filling. The milk temperature changes during the indirect UHT sterilization process are as follows: raw milk (5°C)-preheated to 66°C, steam is directly heated to 137°C for 4S, cooled to 76°C, homogeneous (15-25mpa)-freshly fed milk (5℃) Cool to 20℃-aseptic storage tank-aseptic packaging. When indirect heating is used for sterilization, the preheating, heating, sterilization and cooling of the milk are carried out in different exchange sections of the same heat exchanger. The milk does not come into contact with the heating or cooling medium, which can ensure that the product is not contaminated by foreign substances. Milk heating and milk cooling perform heat exchange, recovering 85% of the heat, which greatly saves steam and cooling water.

 Direct heating: it refers to spraying aseptic steam into the milk under high pressure or spraying the milk into the steam, so that the milk is instantly heated to 140°C, and then enters the vacuum chamber, due to evaporation, cooling immediately, and finally aseptic Homogenize and cool under the same conditions. The specific process flow is: raw milk (5°C)-preheated to 75°C, steam directly heated to 140°C for 4S, cooled to 76°C homogeneous (15-25mpa)-cooled to 20°C-aseptic storage tank -Aseptic packaging.

The sterilized milk after ultra-high temperature sterilization and cooling should be continuously sent from the pipeline to the packaging machine immediately under aseptic conditions. In order to balance the difference between the production capacity of the sterilizer and the packaging machine, a sterile tank can be installed between the UHT sterilizer and the filling machine. Aseptic milk enters the storage tank and cannot be contaminated by bacteria. Therefore, the pipelines and valves entering and exiting the storage tank are The parts in the tank that are in contact with milk must be sterile.

UHT sterilized milk is usually aseptic packaged at room temperature. Aseptic filling is to fill the sterilized milk into an aseptic container under aseptic conditions. This process includes the sterilization of packaging materials or packaging containers. Since the final product needs to have a long shelf life under non-refrigerated conditions, all filling and packaging process must also provide complete protection from light and oxygen. Generally, UHT milk can be packaged in aseptic cartons or aseptic composite bags.