One of the major problems fruit exporters face in the perishable fruit export industry today is lack of evidence that the pre-cooling of fruits was duly done at origin. This often leads to significant losses for exporters as the fruits arrive at their destination with damages and the buyer rejects it. This situation is further worsened by claim rejection from the shipping line for lack of evidence that fruits were precooled at the right temperatures. Fruit exporters must therefore understand that pre-cooling of fruits and vegetables is a critical step in the post harvest cold chain in order to avoid further absorption of losses.
In this article, we will focus on the benefits of precooling fruits and vegetables before export, factors to consider before precooling, the methods of precooling fresh produce and the consequences of failure to observe precooling of freshly harvested produce before export.
What then is pre-cooling?
Precooling is a method of removing “field heat” from freshly harvest produce inorder to slow down metabolism and reduce deterioration prior to transport, storage or processing. Field heat is the temperature difference between the actual temperature of a freshly harvest produce and the preferred optimal storage temperature of the produce. That is why it is very beneficial to understand the importance of pre-cooling fruits and vegetables before export.
Benefits of pre-cooling
- It removes the field heat
- Reduces the rate of respiration and ripening
- Reduces the loss of moisture
- Reduce bruise damage during transits
- Reduces the production of ethylene
- Reduces /inhibits the growth of spoilage organisms
- Eases the load on the cooling system (refrigeration) of transport or storage chamber
- Above factor helps in extending the product shelf life
Factors to consider before pre-cooling
- Air temperature during harvesting (during summer pre-cooling time is more)
- Time between harvest and precooling
- Nature of the crop (High perishable crop require immediate pre-cooling)
- Difference in temperature between the crop and cooling medium
- Nature/Velocity of the cooling medium
- Rate of transfer of heat from the crop to the cooling medium.
- Type of package material used – Use of water proof ventilated boxes for good air circulation in the room is helpful. Treating plastic boxes/ fiberboard cartons with wax will render them waterproof.
Methods of pre-cooling fresh produce
Precooling is a separate operation from refrigeration and requires the use of specifically designed equipment and method. Several effective methods for rapid removal of heat from produce are in commercial use. The choice of method depends largely on the perishability and refrigeration equipment of the product, its adaptability to a specific method and the availability of facilities. Below are some common precooling methods.
Room cooling simply means placing your product in a room colder than the current temperature of the product for a specific time until the current temperature gets down to the desired temperatures. Even though this process can be very slow in comparison to other precooling methods, it is quite efficient in terms of its required use of energy. Room cooling is more suitable for produce that doesn’t rot quickly such as, apples, pumpkins, cabbage, beets, potatoes, peaches, pears.
Hydro-cooling is another method of precooling that involves submerging the produce into chilled water. It is very quick, especially in comparison to room cooling. However, it limits the temperature to which you can cool down produce to. Without additives for instance, you cannot cool water below 32 degree celsius. This renders it ineffective for cooling down a product that requires a temperature lower than to 32 degree celsius. It equally raises the challenge of pathogens that can easily be carried and spread by the water. If your postharvest team decides to adopt the Hydro-cooling method, please note that the best products that will benefit from its impact include; asparagus, broccoli, cabbage, carrots, green beans, cucumbers, Kohlrabi, parsnips, rhubarb, rutabagas, and sweet corn.
Vacuum cooling is the costliest method of precooling. This method uses a vacuum pump which cools down crops rapidly due to the evacuation of the air, which causes a rapid evaporation of water located at the surface of the crops. A disadvantage of this method is the reduction in crop weight of 1% for every 5 or 6 °C reduction in temperature. Lettuce is one of the main vegetables that are commonly vacuum cooled.
Ice injection cooling, more commonly referred to as ice cooling, is the method of mixing ice water into a slurry-like consistency, and then injecting it into the main packaging of the product so that it cools the product directly. Products that can benefit from the impact of this method include; asparagus, broccoli, kohlrabi, green onions, parsnips, radishes, rutabagas and sweet corn.
Also known as blast cooling, it is a method of cooling which is done by creating a pressure difference across the product itself and drawing cold air into the packaging of the product. The various types of fruits that can be cooled using this method include; apples, apricots, avocados, green beans, bell peppers, blueberries, boysenberries, broccoli, brussel sprouts, cabbage, carrots, cantaloupe, cauliflower, celery, chili peppers, cucumbers, figs, grapes, honeydew, kiwifruit, kohlrabi, leaf lettuce, mushrooms, nectarines, olives, peaches, peas, pears peppers, plums, potatoes, raspberies, rhubarb, romaine lettuce, saskatoons, spinach, squash, strawberries, swiss chard, tomatoes.
Consequences of failure to pre-cool fruits before shipment
There are repercusions of failing to pre-cool fruits and vegetables before export. These include:
- Food waste as a result of damage
- Rejection of the fruits and vegetables by the buyer for quality issues
- Claim rejection by the shipping line for lack of evidence of precooling
- Loss of profits and return on investment
- Breach of buyers trust in the exporter
Written by: Terrence Matiete
Claims handler at StilFresh Recoveries