Prepared by: Hamid Salari PRE COOLING Prepared by: Hamid Salari

PRE-COOLING Good temperature management = reduce post harvest losses Field heat = high rate of respiration Rapid removal of field heat Widely used for highly perishable fruits and vegetables Product’s lowest safe temperature

Room cooling is a relatively simple method Needs only a refrigerated room The produce is packed in containers The rate of cooling is rather slow It may take hours or even days to cool depending on: what kind of product it is the size and nature of the container and the temperature velocity of the circulating air.

Forced-air cooling Rapid way of using air to cool produce Cold air is forced to flow through the inside of each container Covered tunnel with and exhaust fan at one end Grapes, strawberries and raspberries are cooled in less than an hour Cooling rate depends on: the air temperature rate of air flow 75-90 percent faster than room cooling Two types are forced air tunnel and serpentine cooling

Hydro-cooling Dumping produce into cold water or running cold water over produce cleaning at the same time reduces water loss and wilting Use of a disinfectant in the water is recommended to reduce the spread of diseases not appropriate for berries, potatoes to be stored, sweet potatoes, bulb onions, garlic Water removes heat about five times faster than air Well water temperatures is in10-15 °C range If hydro-cooling water is recirculated, it should be chlorinated to minimize disease problems.

Top or liquid icing In top icing, crushed ice is added to the container over the top of the produce by hand or machine For liquid icing, slurry of water and ice is injected into produce packages through vents or handholds Icing methods work well with high-respiration commodities such as sweet corn and broccoli One pound of ice will cool about three pounds of produce from 30 °C to 5 °C Water drainage holes are required in the box

Products can be iced Products damaged by direct contact with ice Artichoke Strawberry Asparagus Blueberry Beets Raspberry Broccoli Tomatoes Cantaloupes Squash Carrots Beans Cauliflower Cucumbers Endive Garlic Green onion Okra Leafy greens Bulb onion Radish Lettuce Spinach Herbs Sweet corn Watermelon

Vacuum cooling As the vacuum pressure increases, water within the plant evaporates and removes heat from the tissues This system works best for leafy crops, such as lettuce, which have a high surface-to-volume ratio To reduce water loss, water is sometimes sprayed on the produce prior to placing it in the chamber This process is called hydrovac cooling When the pressure is lowered to 4.6 mm Hg, water “boils” off at 0 °C from all over the leaf surface. The boiling effect draws heat for vaporization The cooling time is usually in the order of 20to30 minutes

Evaporative cooling zero energy cool chamber is working under this principle Disadvantage is cooling limited by water holding capacity of the air.