Preserving food for a long time with almost original quality is always a challenge. Especially in the tropical climate like our country, the best method of quality assurance is refrigeration.


Theoretical basis

There are three main causes of food spoilage:

- Due to the effect of yeast produced by the food itself

- Due to the entry of microorganisms from outside causing food spoilage

- Due to toxins secreted by microorganisms

Among them, the impact caused by microorganisms is the main reason. Microorganisms survive mostly at -10°C to 80°C, so cooling to below -10°C will limit microbial growth.

Post-slaughter food changes

- Physical change: Change in color, shape, food shortage

- Chemical change: The chemical reactions that take place in food

- Physiological change: only occurs with fruits and vegetables, the subjects continue to breathe after harvesting

- Biochemical changes: after death, the temperature of animal cells increases, the heat of decomposition is greater than living organisms leads to decomposition. This phenomenon occurs strongly in aquatic products and seafood. Therefore, the faster the cooling, the slower the food decomposes and improves the preservation quality.

Animals after slaughtered go through 3 stages: frostbite, ripening and decomposition

+ Frostbite: is the process of physiological-chemical changes after death that causes muscles to contract. It takes a few minutes in fish, and for beef and pork, it can take up to tens of hours.

+ Ripening: then the meat begins to soften. In fish, it turns to decomposition immediately without ripening stage. It is best to use meat at this stage (preserved meat after 2 days has a delicious taste, after 5 days has a good taste...)

+ In decomposition stage, the temperature increases and the cells begin to decompose. The reaction speed is intense at the temperature of 36°C to 37°C.

Freezing methods

Depending on the freezing methods, it is divided into slow freezing, fast freezing, 1-phase freezing and 2-phase freezing.

General characteristics of freezing technology

For aquatic products and seafood, there is no main stage after catching, but from frostbite to decomposition (or the main stage to very short in only a few tens of minutes). So in general, if this product is not refrigerated or processed immediately after catching, it will decompose within 3 to10 hours.

The lower the temperature, the higher the inhibition of the decomposition and invasion of microorganisms. For every 10°C decrease in temperature, the decay decreases by ½ to 1/3.

Aquatic products and seafood need to be frozen quickly (0.1+4h)

For aquatic products and seafood, some types of mold still exist at a temperature of -10°C with 15% water, so these products must be stored at a temperature of -18°C to 25°C (amount of water < 15%)

Meat refrigeration technology

Refrigeration method is used when it is necessary to preserve fresh meat for a short period of time from a few days to a few weeks.

General principles

To maximize meat quality and extend its shelf life, meat should be cooled down to near the freezing point that corresponds to that type of meat.

The quality and shelf life of frozen meat depends on the cooling rate and the packaging type.

Basic requirements of meat refrigeration technology

Refrigerate meat immediately after slaughter and primary processing aims to lower the surface temperature of the meat as quickly as possible.

Refrigeration time is as short as possible to ensure minimal loss of weight and preserve the fresh color of the meat.

To promote the ripening and create the tenderness and characteristic flavor of the meat, keep the meat at 12°C for 15 hours. In this process, it can be combined with the stages of grinding, mixing meat, and packaging.

Classification of refrigerated meat

- Fresh meat: meat directly after slaughter has an average temperature with T = 35°C

- Meat is cooled in the TB normal environment usually by fan with T=25+28°C

- Cooled meat, processed and refrigerated meat with T=0+4°C

- Over cold meat (partially frozen), processed and refrigerated meat with T=-2±0.5°C



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