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



Evolution of Heat by Commodity 



In any consideration of the storage of fresh fruits and vegetables, 

 cut flowers, etc., it should be remembered that these commodities are 

 alive and that by virtue of that fact they carry on within themselves 

 many of the processes characteristic of all living things. Unless the 

 relative humidity is high, they give off moisture to the surrounding 

 air and most of them, in time, become shriveled or wilted, even at 

 32° F. The enzymes or ferments they contain act on various sub- 

 stances in their tissues and gradually bring about changes in color, 

 texture, and chemical composition which ripen the commodity and 

 may result in serious deterioration or even complete break-down. 

 The most important of these changes are produced by respiration, 

 the process in which the oxygen of the air is combined with the carbon 

 of the plant tissues, occurring chiefly in sugars, to form various de- 

 composition products and eventually carbon dioxide and water. Dur- 

 ing this process energy is released in the form of heat, the amount 

 of which varies with the commodity and increases as the temperature 

 increases, up to about 100°. This heat is always a part of the re- 

 frigeration load which must be considered in handling fruits, vege- 

 tables, and cut flowers in cold-storage rooms or refrigerator cars. 

 The approximate rate of evolution of heat by various commodities is 

 given in table 1. 



Table 1. — Approximate rate of evolution of heat ~by certain fresh fruits and 

 vegetables lohen stored at the temperatures indicated 



Commodity 



Apples 



Bananas: 



Green 



Turning 



Ripe 



Beets 



Cantaloups 



Carrots 



Celery 



Cherries (sour) 



Grapefruit... 



Grapes: 



Cornichon and Flame Tokay.. 



Sultanina 



Emperor 



Ohanez 



See footnotes at end of table. 



Tempera' 

 ture 



F. 

 32 

 40 

 60 

 85 



f54 



IfiS 



Heat evolved per 



ton of fruits or 



vegetables per 24 



hours* 



British thermal 

 units 

 660 to 880 

 1,110 to 1.760 

 4, 400 to 6, 600 

 6, 600 to 15, 400 



Litera- 

 ture ref- 

 erences 



3.: 



1, 



1, 

 3, 

 2, 

 4, 

 24, 



1, 

 3, 



2, 

 5, 



1, 320 to 1, 

 L, 000 to 13, 



1, 

 2, 



4, 

 660 to 1, 



2, 200 to 2, 

 5, 500 to 6, 



• 1, 

 16, 



15, 



(46) 

 (52) 



(0) 



(35) 

 (30) 

 (25) 



(°) 



