8 CIRCULAR 2 7 8, U. S. DEPARTMENT OF AGRICULTURE 



a+0.20 in which .S signifies the specific heat of a substance contain- 

 ing a percent of water; 0.2 is the value which has been assumed to 

 represent the specific heat of the solid constituents of the substance 

 in question (#0). 



Column 1 of table 2 shows the kind and variety of fruit and col- 

 umn 2 the temperature of the fruit at the time cooling starts, in a 

 room held at 32° F. The next column shows the amount of heat 

 evolved by respiration if the fruit reaches 35° at the end of 3 days. 

 The next five columns show the amount of heat if cooling to 35° re- 

 quires 4, 5, 6, 8, or 10 days, respectively. The last column is the 

 sensible heat (obtained by multiplying the specific heat of the fruit 

 by the difference between initial and final temperatures and this 

 result by the number of pounds in a ton). For any one kind of 

 fruit at a given initial temperature, the specific heat is assumed to be 

 the same for all the cooling periods included in the table. 



The values given in table 2 are only approximate. The two as- 

 sumptions that have been made — namely, (1) that the heat of respira- 

 tion is produced only by the oxidation of a hexose sugar and can be 

 computed from observed amounts of carbon dioxide produced, and 

 (2) that the rate of temperature drop is always proportional to the 

 difference between fruit temperature and room temperature — prob- 

 ably lead to fairly accurate results ; but since only a few direct measure- 

 ments of the heat produced by fruits and vegetables have been made, 

 it is not known just how close the approximation is. The figures are 

 presented to help cold-storage-plant operators estimate the quantity of 

 refrigeration required for cooling the specified fruits under the various 

 conditions given. As an example of how the figures can be used, the 

 following calculation may be of interest: A ton of Bartlett pears cooling 

 from 70° to 35° F. in 10 days in a 32° room is shown to be capable of 

 producing about 54,000 B. t. u. Its sensible heat at 70° (35° above its 

 final temperature) is 61,000 B. t. u. The sum of the two is 115,000 

 B. t. u. If this be multiplied by the capacity of the room in tons of 

 fruit, say 600 (the capacity of some of the commercial cold-storage 

 rooms in the United States) and divided by 288,000 (the number of 

 British thermal units in a ton of refrigeration), the quotient 239 is 

 obtained; this is approximately the number of tons of refrigeration 

 required to cool 600 tons of Bartlett pears to 35° in 10 days under the 

 conditions specified. The corresponding figure for Winesap apples is 

 177 and that for Grimes Golden apples, 200. 



EFFECT OF COLD STORAGE ON SUBSEQUENT BEHAVIOR OF FRUITS AND 



VEGETABLES 



The belief is rather common among those concerned with the mar- 

 keting of fresh fruits and vegetables that commodities of this kind 

 that have been in cold storage deteriorate more rapidly after removal 

 from the low temperature than if they had been held at ordinary 

 temperatures. It is difficult, however, to find a basis for judging 

 whether or not they actually do so because there is no means known 

 other than the use of low temperature for checking the ripeningand 

 decay so largely responsible for their deterioration — that is, it is 

 impossible in the present state of knowledge to obtain fruits and 

 vegetables that have not been refrigerated but still have not changed 

 in any way s:.ice harvest, for comparison with similar lots that have 

 been in cold storage and are eventually removed. 



