Temperature Effects on Produce Degradation 615
The nature of the product is a major determinant in the selection of a cooling
method.^25 Different types of produce have different cooling requirements. For exam-
ple, strawberries and broccoli require near-freezing temperatures, while such low
temperatures may damage summer squash and tomatoes. In addition, some products
are damaged by exposure to water that is used as the cooling medium in some
cooling methods.
20.3.2.1 Cold-Air Cooling
Cold-air cooling, in the forms of room cooling or forced-air cooling, is the most
widely adaptable method of precooling and is commonly used for many fruits and
vegetables.^24 In this cooling method the cooling medium, refrigerated air, surrounds
the produce packed in boxes or pallet bins. Cold air cooling is the least energy-
efficient type of cooling but is widely used because it is adaptable to a wide range
of products and packaging systems.
Room cooling is most commonly used for products with a relatively long storage
life that will be cooled and stored in the same room.^1 Examples of such products
include potatoes, sweet potatoes, citrus, and controlled-atmosphere-stored apples.
Room cooling is generally sufficient for keeping produce at a low temperature once
it has been cooled, but it often does not remove field heat rapidly enough to maintain
the quality of highly perishable crops. In the room cooling process, heat is removed
slowly from only that produce near the outside of the container.^25 Near the center
FIGURE 20.5Typical time–temperature pattern for cooling produce to 7/8 of the difference
between its original temperature and the cooling medium in 9 h. (Adapted from Thompson,
J.F., Pre-cooling and storage facilities, in The Commercial Storage of Fruits, Vegetables, and
Florist and Nursery Crops, Gross, K.C., Yang, C.Y., and Saltveit, M., Eds., Agricultural
Research Service, Beltsville, MD, 2002, draft version of revised USDA Agriculture Handbook
66, available at http://www.ba.ars.usda.gov/hb66/index.html. With permission.)
3
Hours of cooling20151050
0 6 9 12 15Initial product temperatureAverage product temperature1/2 cool3/4 cool7/8 cool
15/16 coolTemperature ( Air temperature°C)