Vacuum precooling characteristics

Vacuum pre-cooling is to place the fruits and vegetables in a vacuum chamber, and use a vacuum pump to evacuate the chamber. When the indoor vacuum reaches the saturation pressure of the water vapor corresponding to the temperature of the fruits and vegetables, the moisture in the fiber gap of the surface of the fruits and vegetables begins to evaporate. Take away the latent heat of evaporation, reduce the temperature of the fruits and vegetables, and further reduce the pressure until the fruits and vegetables are cooled to the required temperature.

Vacuum pre-cooling features:

(1) The cooling speed is fast. It takes only 20~30 minutes for the fruits and vegetables to cool from room temperature to 0 °C.

(2) Cooling evenly. The temperature difference between the center and the surface of the fruit and vegetable is small when cooling.

(3) Good quality. The fruits and vegetables after cooling have no loss of protein, sugar, lipids and vitamins.

(4) Sanitary cleaning. Because the pre-cooled fruits and vegetables are in a vacuum environment, the vacuum environment can sterilize or artificially breed bacteria.

(5) Low dry consumption. Vacuum pre-cooling can control the evaporation of water in fruits and vegetables by controlling the degree of vacuum, or spray an appropriate amount of water to fruits and vegetables before pre-cooling. The dry consumption of fruits and vegetables can be controlled within 2~3%. The average cooling consumption is more than 10%.

(6) Not subject to packaging restrictions. Fruits and vegetables packed in cartons, plastic bags, etc., have a vacuum cooling rate that is not different from unpackaged fruits and vegetables.

In practical application, it is proved that the vegetables pre-cooled by vacuum have a dry surface. Fresh green is obviously different from the vegetables that directly enter the cold and slowly cool down.

Vegetables with small body/table ratio, such as cabbage, spinach, leeks and other leafy vegetables, are particularly suitable for vacuum precooling.

The vacuum pre-cooling equipment is mainly composed of a vacuum chamber, a vacuum system, a refrigeration system and a control system. The function of the refrigeration system is to provide a cooling capacity for the water vapor trap, so that the water vapor evaporated from the fruits and vegetables in the vacuum chamber is in the cooling coil of the water vapor trap. Condensate and discharge the condensate without being sucked into the vacuum pump, affecting the pumping performance of the pump.