Pre-cooling refers to the rapid removal of field heat from freshly harvested commodities before packing and distribution and storage and is essential for horticulture crops to preserve their freshness, quality and post-harvest life.

For many fresh horticulture commodities, one hour time loss at the field temperature of 30°C between harvest and pre-cooling can reduce produce life by as much as 8-24 hours.

Delay in pre-cooling results in loss of moisture from the produce causes weight loss and combined with active micro-biological organisms result in deterioration of quality and value loss.

Conventional cold stores and refrigerated transport systems neither have the refrigeration capacity nor the air circulation needed for pre-cooling/ rapid cooling of fresh horticulture produce.

There are three main methods used for rapid cooling of fresh produce;

Forced air cooling

Hydro cooling

Vacuum cooling

Great care needs to be taken to ensure the correct cooling methodology. Forced air cooling is the most commonly used method but poor system design can result in dehydration during the cooling process or uneven cooling times. High relative humidity of the cooling air is a vital factor in the design of forced air cooling systems and high humidity coolers are an essential part of the design.

Hydro cooling is most commonly used for root vegetables and should be viewed as a continuous and in line process. Water flow and filtration are very important in achieving the required cooling times which can be as low as five minutes for asparagus and fifteen minutes for carrots.

Vacuum cooling is the least common method used. It is an extremely rapid method of cooling and used in large scale operations for cooling lettuce or other leafy products. One problem in the conventional set up for every 5 °C temperature reduction the product will lose around 0.9% of its moisture. This can be a problem with high incoming temperatures and can be overcome to an extent by adopting a variation of conventional vacuum cooling, often known as hydro vac.