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Freeze food with liquid nitrogen

Freeze food with liquid nitrogen

Cập nhật: 05-08-2021 03:38:23 | News | Lượt xem: 10

Freezing food with nitrogen gas, Freezing with a mixture of ice and salt... is one of the freezing methods.

Freezing process in food production
Freezing in food production is the process of lowering the temperature of a food product to freezing for the purpose of processing and preservation. This method has been used for many centuries and is licensed. Patent in England as early as 1842 for the preservation of food by immersion in salt water and ice. However, it was not until the advent of air conditioning that this process was widely applied in the world.

In 1880, a shipment of meat was shipped from Australia to England. Stored in the refrigerator was accidentally frozen. The meat quality is so good that this procedure is immediately applicable to long-distance storage and transportation processes. In Vietnam, the freezing process is widely used in processing industries. And preserve frozen food such as seafood, meat, some fruit and vegetable products.

It plays an important role in processing and preserving food products.
With an important role in processing and preserving food products. The process of freezing food products today is widely used all over the world in general and Vietnam in particular. From an economic perspective, frozen food. In recent years, it has really become an important economic sub-sector of Vietnam, mainly for export.

According to some statistics, Vietnam's frozen food market . It is growing at a rate of 20 to 40% per year. Already present all over the world, especially the US, EU, China, and Japan markets. Since then, forming large grazing areas of cattle, pangasius, shrimp..., providing jobs and stable income for the majority of workers. Frozen foods are also available in supermarkets. Specialized stores nationwide, are part of the needs of modern life.

Principles of freezing food
Meat, poultry, seafood, vegetables, tubers and fruits are perishable foods. They are perishable because they are composed of organic substances such as: . Protein, fat, carbohydrates, vitamins, inorganic substances such as water, mineral salts. At room temperature, food is rapidly decomposed by proliferation. And thrive of microorganisms and biochemical processes. When the temperature is low, it will inhibit and inhibit the activity of enzymes in the food itself and microorganisms. Reduces the vital activities of cells, thereby slowing down or stopping the transformation processes that cause spoilage and putrefaction. Frozen food

It is calculated that for every 10 degrees Celsius decrease, the rate of biochemical reactions decreases. And from 1/2 to 1/3 and most microorganisms are inactive in the range of -3 degrees C to -10 degrees C. Molds tolerate cold better than about -15 degrees C and less humidity. at least 15%. However, it is necessary to lower the temperature to -18 degrees Celsius for the water in the food to have a moisture content of 14%. Therefore, the best storage temperature is from -18 degrees Celsius or less. New causes most microorganisms and molds to completely stop working.

Frozen food
Water in food exists as a solution (dissolving mineral salts). It fills the space between the molecules that make up each food. Water facilitates physical and chemical processes and biochemical reactions. And it is a favorable environment for the growth of microorganisms. The composition of water in different foods is very different such as: . In livestock and poultry meat from 52-75%, seafood from 60-85%, vegetables from 65-95%.

The main purpose of food freezing is to reduce the temperature. And at the same time freeze the amount of water in it, so it inhibits the growth of microorganisms. Activate enzymes, reduce the rate of biochemical reactions. To preserve food products for a longer time in a low temperature environment. The freezing point of foods varies from food to food. Usually less than 0 degrees Celsius because they have a concentration of mineral salts and solutes in the cell fluid. For example, sea fish has a freezing point of about -1.5 degrees Celsius. Freshwater fish has a freezing point of -1.0 degrees Celsius, marine shrimp is -2 degrees Celsius. Freezing food

Mechanism of freezing in food when freezing
When the food temperature is lowered, the sprouts crystallize. Will begin to appear in the spaces between cells (intercellular). When the temperature drops to the crystallization point, most of the water in the intercellular space crystallizes. Increases the concentration of solutes inside the cell than outside the cell. Therefore, under osmotic pressure, water in the cell tends to flow out of the intercellular space through the semi-permeable membrane. Frozen food

If freezing quickly:
With fast freezing speed from 1 to 3 cm/h. And the freezing time is from 2 to 6 hours or the freezing speed is greater than or equal to 15cm/h. Freezing time is less than 20 minutes. At that time, the crystal nucleation process takes place very quickly, little or no water diffuses to the outside. Create many crystalline sprouts, fine, even. This method has little effect on product quality. Frozen food

If freezing is slow:
Freezing speed less than 0.5 cm/h and freezing time greater than 10 hours. The water in the cell then flows out of the cell. The accretion makes the intercellular ice crystals grow larger without creating new ice crystals. Therefore, large ice crystals can compress and tear the cell membrane. Deformed muscle tissue structure, greatly affecting product quality. At the temperature range of -1 to -2 degrees C the crystals form large sizes. At a temperature of -10 to -20 degrees C the crystals are numerous and small in size.

Fresh food frozen and frozen will have the highest quality. Because the structure and the connection of water with the components are still solid. But with poor quality food, the ability to hold water decreases. The percentage of free water increases, the structural elasticity decreases. At that time, the water of crystallization will diffuse a lot, the cell topology is torn and broken by the ice crystals. Therefore, when thawing, the food structure is soft and less elastic. Freezing food

The process of losing water when freezing
When the water has not frozen, there is evaporation of water from the surface of the food. Out to cold environment due to temperature and humidity difference. Once the water has frozen, there is movement of water from a place of high temperature to an area of ​​low temperature. Increases the amount of free water, reduces the amount of bound water. When thawing, part of the water cannot return to its original position. Due to the structure and properties of the substances have been changed resulting in mass loss. Also during storage there is ice sublimation. If the difference between the surface temperature of the product and the air in the freezer is larger, the more moisture will evaporate, causing mass loss. Frozen food

Methods of freezing
Fish is rapidly frozen by liquid nitrogen spray conveyor belt, in Germany in 1970

Some of the freezing methods are listed below:

Freezing food in cold air: food is convective heat transfer by cold air flow.
Contact freezing: product is placed on trays and sandwiched between freezer shakers. (inside empty shakers with refrigerant flowing through, -40 to -45 degrees Celsius evaporator)
Cryogenic: the food is moved on conveyor belts and sprayed with liquid nitrogen with a very low evaporation temperature of -196 degrees Celsius, so the cooling time only lasts 5 to 10 minutes.
Freeze with a mixture of ice and salt.

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