1. Prepared by: Hamid Salari
PRE COOLING
Prepared by: Hamid Salari

2. 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

3. 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.

4. 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 percent faster than room cooling Two types are forced air tunnel and serpentine cooling

5. 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.

6. 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

7. 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

8. 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

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