Precooling

To achieve maximum storage for a crop and reduce losses during its marketable life it is essential to keep it at the most appropriate temperature; this is usually just above that which will cause chilling or freezing injury.
To maximize effect the crop should be brought to that temperature as quickly as possible after harvest. This is known as precooling.

The rate of precooling depend on:
 The difference in temperature between the crops and cooling medium.
 Accessibility of the cooling medium to the crops.
 The nature of the cooling medium.
 The velocity of the cooling medium.
 Rate of transfer of heat from the crops to the cooling medium.
Heat can be transferred from the crop in 3 ways: Conduction, Convection and radiation. In pre-cooling conduction is responsible for heat transfer, which is direct movement of heat from one object or substance to other to another by direct contact. A crop having relative large mass and a small surface area will be cooled more slowly than if it had a smaller mass and large surface area.. This is because in the former the heat from the inside the crop has to move to the surface before it is transferred.
Heat in the crops comes either from convection from air surrounding from sun or from the metabolic heat from the inside the crop.