Cooling Methods

The main methods of cooling are:

  • Hydrocooling

  • Vacuum cooling

  • Wet air cooling with positive ventilation, including ice bank cooling.

Hydrocooling
Hydrocooling is a continuous process in which the produce is cooled by either immersion in, or drenching with cold water. This may be followed by a clean water rinse.
Only crops such as carrots, watercress and in some cases tomatoes, that can be washed or handled in water, are appropriate for hydrocooling.
Hydrocooling can make heavy demands on electrical power, but an ice bank may be used to reduce the peak          requirement.
The cooler should be designed so that it does not restrict the throughput of the packing line.
Remember that the wet produce will deteriorate rapidly if it is not kept cool.

Cooling times - 20 to 40 minutes. Low volume products cool faster than large ones.

Vacuum cooling
Vacuum cooling is a batch process which relies on the cooling effect of the evaporation of water from the produce. A weight loss of about 1 per cent occurs for every 5°C the produce is cooled.
Leafy crops, like lettuce, which have a large surface area and contain much free water, are most suited to vacuum cooling. The system is unsuitable for bulky crops or those with a thick waxy surface.
Handling produce into and out of the cooling chamber must be well organised to achieve maximum throughput. Coolers with doors at each end can simplify handling.
The cooling of mixed products in the same batch may result in insufficient cooling or freezing of parts of the load.
Some crops may be sprayed with water before cooling to minimise the weight loss.
Cooling times - 20 to 40 minutes, depending on the type of crop and equipment capacity.

Air cooling, conventional cool stores
In these, produce is cooled by exposure to cold air which is circulated inside an insulated room. Heat is extracted from the air by a refrigerated cooler. The cooling performance of cool stores is enhanced by positive or forced  ventilation. This ensures that cooling air comes into close contact with the produce. Extended exposure can lead to desiccation, so produce should be protected, usually with film plastics.
All produce can be cooled in a conventional cool store but the process flow is slow. Forced ventilation will increase desiccation unless produce is well protected. Other methods are preferable for fast uniform cooling.