In order to extend the shelf life of fruits and vegetables, reduce moisture loss and circulation of various losses, enabling consumers to obtain a high degree of clean fresh fruits and vegetables, it must be a series of post-harvest processing in the factory, such as the selection of , root bark leaf stalks, cleaning pre-cooling, water treatment, packaging, pre-cooling process is therefore essential. In refrigerated or frozen before the temperature of the food from the original (such as fruits and vegetables within 24 hours after harvest or livestock slaughtered temperature after the temperature) is rapidly cooled to a predetermined temperature, in a timely manner to inhibit biochemical reactions and microbial food itself reproduction. Cooling methods are commonly used:

　　① air cooling method, tunnel ventilation blowing cold food is placed, or 1300 ~ 2000Pa pressure difference, so that there is cold air into and through the transom of food packaging, to accelerate cooling. Cold air temperature, relative humidity and flow rate is determined according to the type of food, the food is generally not to freeze, usually a relative humidity of 90 to 95%.

　　② water cooling method, with water as the heat transfer medium, large-capacity pumps to make closer to 0 ℃ cold water sprayed on the product. Because heat capacity of water is much greater than air, high heat transfer efficiency, most of the food can be cooled within 10 to 15 minutes. When the fish with seawater cooling, speed, temperature uniformity, and extended storage period.