FORCED AIR PRECOOLING
Pre-cooling refers to the rapid removal of field heat shortly after the harvest of a crop. Field heat can be defined as the difference in temperature between the temperature of the crop harvested and the optimal storage temperature of that product. In general the temperature should be cooled down till it reaches 88% of the existing difference in temperature and its optimal storage temperature. Field heat should be removed as fast as possible since, for most produce, an hour delay at field conditions of about 35°C will lead to a loss in shelf-life of about 1 day – even at optimal storage conditions.
According to the Indian Board of Horticulture, especially grapes, mandarins, berries, cherries, leeches, melons, stone fruits, sapotas, okra, tomatoes, capsicum, chilli peppers, eggplant, cucumbers, green beans, peas, and spinach should be rapidly pre-cooled, whereas other, less perishable produce is made up of mangoes, papaya, guava, green bananas, pomegranates, radish, cabbage, cauliflower and carrots.
Pre-cooling benefits include:
- Lowering the required workload of a cold storage since optimum storage temperature is reached more quickly.
- Restricting and minimizing respiratory activity, thereby conserving the weight of the produce, and enzymatic degradation of the produce harvested; thus preventing softening, water loss and wilting.
- Preventing microbial growth, such as bacteria and fungi thereby decreasing the rate of decay.
- Decreasing rate of ethylene production and the impact on ethylene sensitive produce.
- Delaying chilling injuries for certain fruits.
- Increasing the daily intake into storage facilities which should not exceed 10% of its cooling capacity if produce is not pre-cooled.