The Principle of Vacuum Pre-cooling in Food Preservation Technology

With the advancement of cultivation technology and refrigeration technology in recent years, the popularization of greenhouse cultivation and the development of transportation capacity, people have more requirements for fruit and vegetable freshness, appearance and taste. 

Affected by the trend of returning to nature and being close to nature, the demand for fresh vegetables, green food and pure natural food has risen rapidly, all of which have brought new challenges to the production, storage and transportation of vegetables and fruits.


This article is about the principle of vacuum pre-cooling in food preservation technology and its advantages.


  1. What is Vacuum Pre-cooling  

Vacuum pre-cooling means that under normal atmospheric pressure (101.325kPa), water evaporates at 100°C. If the atmospheric pressure is 610Pa, water evaporates at 0°C, and the water boiling point decreases with the decrease of ambient atmospheric pressure. Boiling is rapid evaporation, which absorbs heat rapidly.

Fresh fruits and vegetables are placed in airtight containers, air and water vapor are quickly drawn out. As the pressure continues to decrease, the fruits and vegetables are cooled by the continuous and rapid evaporation of water.


  1. Why Pre-cooling is Necessary?  

Vegetables and fruits are rich in vitamin C, carotene, minerals and various enzymes that promote digestion. After fruit and vegetables are picked, due to the influence of field heat, their temperature is relatively high, coupled with their own respiration, the composition is constantly changing.

At the same time, the heat released is also increasing, and the temperature continues to rise. The higher temperature promotes its respiration to speed up, continue to release heat, a large amount of water evaporates, fruits and vegetables shrink rapidly, and their freshness decreases until they become corrupt.    

Pre-cooling is an effective measure to quickly remove field heat, inhibit its respiration, maintain the freshness of fruits and vegetables, and prolong the storage period. Replacing normal temperature or conventional cold storage with pre-cooling and fresh-keeping is an important guarantee for increasing the supply of high-quality fresh vegetables and fruits and improving the health level and life quality of the whole nation.  


  1. The Principle of Vacuum Pre-cooling  

The water loss of vacuum pre-cooling is generally about 3%, which will not cause the fruits and vegetables to wilt and lose their freshness. Due to the pressure difference inside and outside the fruit and vegetable tissue, the harmful gas and heat in the tissue are also drawn out, which can delay the arrival of the climacteric respiration peak of the fruit and vegetable. In this way, the cooling is carried out from the inside of the tissue to the outer surface at the same time, that is, uniform cooling, which is unique to vacuum cooling, so food has Long shelf life.  


  1. Vacuum Pre-cooling Features  

  • The preservation time is long, and it can be directly transported without entering the cold storage, and the insulation car can be used for short and medium-distance transportation.

  • The cooling time is very fast, generally only 20 minutes, and any packaging with air vents can be used.

  • Keep the original sensory and quality (color, aroma, taste and nutrients) of fruits and vegetables best.

  • It can inhibit or kill bacteria and microorganisms

  • It has a "thin layer drying effect". Some small injuries on the surface of fruits and vegetables can be "healed" or will not continue to expand.

  • No pollution to the environment

  • Low operating cost

  • It can prolong the shelf life, and the vegetables pre-cooled can go directly to high-end supermarkets without refrigeration.


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