After harvesting, it’s essential to properly cool produce in order to maximize its shelf life. By staving off the natural growth of microorganisms, the cooling process helps to slow the physiological changes which impact freshness and nutritional value. This can be achieved both through lower-cost and more advanced methods, including harvesting during cooler periods during the day, cool air ventilation, and evaporative cooling. For many types of produce, however, precooling is an essential part of the equation. Precooling is a process performed to rapidly remove field heat immediately following a harvest.

Field heat is described as the difference between the temperatures of actual crops harvested versus the ideal storing temperatures for those same food products. Prompt removal of this type of heat is essential, as even an hour-long delay can correlate with about a day’s loss in terms of shelf life. As the name suggests, precooling is performed in advance of the final, primary cooling method, and it can be performed in several different fashions.

Precooling Methods

There are various approaches to precooling, and while they vary in their effectiveness, any process which quickly lowers the temperature of harvested produce without damaging them is beneficial to some extent. Semco provides a range of industrial cooling products, such as hydrocoolers which deliver efficient, economical performance to maximize yield and minimize loss.

Hydrocooling – Hydrocooling is one of the most common and effective precooling methods. Hydrocooling involves spraying produce or dipping it into chilled water. This method can work up to 15 times faster than air-cooling methods. Hydrocooling also does a better job of retaining moisture and can even utilize refrigerated calcium chloride solutions in order to prevent storage problems with certain fruits. Hydrocooling does require a clean, sanitary water source and is best used for flower, stem, and root-type vegetables as well as some tree fruits.

Some other common precooling methods are described below:

Shade Cooling – By moving produce to a cool, shaded area immediately after harvesting, an acceptable amount of precooling can sometimes be achieved, depending on the produce. If possible, create viable indoor holding areas such as within packing houses. Structures which are outfitted with light-colored or white roofs are also generally better for reflecting sunlight and reducing solar gain, lowering inside temperatures with minimal overhead cost.

Ice Cooling – Ideal for use during storage, distribution, and transport stages, ice cooling is an acceptable method of field heat removal, particularly when produce packaging is too dense for effective air-based approaches. As much of the cooling potential is lost via heat exchange with the general environment as opposed to the produce itself, ice is not generally regarded as a highly-efficient method of precooling.

Ice cooling can be performed in several different fashions, including top icing, applying crushed ice over produce, or liquid icing, injecting a slushy ice and water mixture into packages, or by wrapping ice bottles in paper and placing them amid produce, such as in situations where direct contact is to be avoided.

Specific Produce Types That Require Precooling

Precooling is an important step in the harvesting process for many fruits and vegetables. Among those that should always be precooled are the following:

  • Berries
  • Capsicum
  • Cherries
  • Chili peppers
  • Cucumbers
  • Eggplant
  • Grapes
  • Green beans
  • Leeches
  • Mandarin oranges
  • Melons
  • Okra
  • Peas
  • Sapotas
  • Spinach
  • Stone fruits
  • Tomatoes

Conversely, some types of produce do not typically require precooling. Such produce includes cabbage, carrots, cauliflower, green bananas, guava, mangoes, papaya, pomegranates, and radishes. Keep in mind these lists are not exhaustive but are helpful starting points for reference. For more detailed information about cooling and storage methods for specific types of produce be sure to check out our past articles.

More Information about Precooling

Semco is a trusted manufacturer of custom-spec cooling systems for storage and transportation of all types of produce and perishable food products. We design hydrocooling technology which will help you to deliver more fresh, high-quality produce while reducing potential losses. Taking a careful, active role in cooling and precooling will help to improve produce taste, quality, and even economic value.