Precooling

Respiration and the loss of water and quality all accelerate as produce warms, so produce left at field temperature ages fast. Cold storage slows this decline, but a store is generally not designed to remove large amounts of heat quickly; if warm produce is simply loaded into a cold room, the centre of the load can stay warm for a long time and deteriorate. Precooling uses methods built for rapid heat removal so the whole product reaches a safe temperature promptly.

Removing field heat early also reduces water loss and wilting, slows the development of decay, and limits ripening in climacteric fruit. Because the benefit is greatest right after harvest, precooling capacity is often located close to the field or packhouse.

Forced-air cooling

Cold air is pulled through vented packages, cooling produce faster than still-air room cooling; widely used for many fruits and vegetables.

Hydrocooling

Produce is showered or immersed in cold water; fast and effective for tolerant crops, but water must be kept clean to avoid spreading decay.

Room cooling

Produce is cooled in a cold room by circulated air; simple but slower, and best suited to less perishable items.

Package icing and vacuum cooling

Ice is added to packages, or leafy crops are cooled by evaporating water under vacuum; each suits particular commodities.

The right method depends on how perishable the crop is, how it is packed, and whether it tolerates wetting. Vacuum cooling, for instance, works well for leafy vegetables with a large surface area, while hydrocooling suits sturdy items that can be wetted.

• Cool produce as soon as possible after harvest to capture the greatest benefit.
• Match the method to the commodity, packaging, and whether the crop tolerates water.
• Keep hydrocooling and icing water clean to avoid spreading decay organisms.
• Move precooled produce promptly into cold storage or refrigerated transport to hold the temperature gained.