Cold Storage

Storage and precooling of produce in a cold room are two distinctly different processes. Once fruit have been precooled, they should remain in cold storage to maintain quality and increase storage life. Cold-temperature storage can be attained through the use of a mechanical refrigeration system that works on the principle of a liquid absorbing heat as it changes states to a gas. Most commonly, a ha-lide refrigerant or ammonia is compressed into liquid form and then released to a gas state under the control of an expansion valve. A series of coils within the refrigerated storage area serves as the mechanism in which this expansion and absorption of heat occurs. As the liquid refrigerant evaporates to a gas within the coils, heat from the fruit is absorbed. Within the closed system, the heated vapor refrigerant is compressed, and a process of condensation removes heat. The cooled refrigerant is compressed to liquid form, and the process repeats itself. The process of maintaining cold-temperature storage requires less horsepower and uses less energy than precooling. Research shows that cycling fans within a cold-storage room or using variable frequency drives can reduce the total energy consumed by motors without affecting fruit quality.

Storing temperate fruit requires careful coordination with respect to temperature (Table S3.1). It is important to maintain specific temperatures that do not drift appreciably above or below set limits. Being off by a degree for an extended period of time can have serious ramifications for the potential storage life and the commercial viability of the fruit itself. In most cases, it is better to be slightly high in the target range than slightly low. Peach storage operators are specifically warned to avoid the temperature range of 2 to 8°C, as peaches stored within this range can develop a serious malady termed "woolli-ness." Most apples are stored close to 0°C. Dense apples such as 'Braeburn', 'Fuji', and 'Granny Smith' are sensitive to internal carbon dioxide buildup and are usually stored at elevated temperatures of 2 to 3°C.

TABLE S3.1. Physical properties and storage considerations for temperate fruit

% Water Content

Highest Freezing Point (°C)

Storage Temperature (°C)

% Relative Humidity in Storage

Approximate Storage Life

Apples

84.1

-1.5

-1.0-4.0

90-95

1-12 months

Apricots

85.4

-1.0

-0.5-0.0

90-95

1-3 weeks

Cherries, sour

83.7

-1.7

0.0

90-95

3-7 days

Cherries, sweet

80.4

-1.8

-1.0--0.5

90-95

2-3 weeks

Nectarines

81.8

-0.9

-0.5-0.0

90-95

2-4 weeks

Peaches

89.1

-0.9

-0.5-0.0

90-95

2-4 weeks

Pears

83.2

-1.5

-1.5-0.5

90-95

2-7 months

Plums

86.6

-0.8

-0.5-0.0

90-95

2-5 weeks

Source: Hardenburg, Watada, and Wang, 1986.

Source: Hardenburg, Watada, and Wang, 1986.

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