COLD STORAGE FOR APPLES AND PEARS 3 



necessarily are greatly condensed in a publication of this kind. For 

 this reason, attention is called to other publications on refrigeration 

 engineering and fruit storage (3, h, 5, 7, 8, 10, 11, 12, IS, 1J+, 15, 16, 

 17,18,20,21,23,U,25.y 



RESPONSE OF FRUIT TO STORAGE CONDITIONS 



Before undertaking to design and operate a cold-storage plant, 

 the nature of the product to be stored must be understood. Apples 

 and pears are alive at the time of harvest ; the length of time they may 

 be held for consumption in the fresh state depends upon how long 

 the end of their life can be delayed. Their storage life dates from 

 the day they are picked, even though they may remain temporarily in 

 the orchard or packing house. The length of storage life varies with 

 the variety, orchard, district, and conditions of growth, the stage of 

 maturity at which the fruit is picked, and the temperature at which 

 it is held. 



Respiration and Ripening Processes 



When an apple or pear is harvested at a desirable stage of maturity 

 its tissue consists largely of water and such carbohydrates as sugars, 

 fruit acids, and, in and between the cell walls, celluloselike substances 

 from which pectins are produced. These carbohydrates cement the 

 cells together, and the degree of adhesion or disintegration of the 

 cells determines whether the flesh of a fruit is firm, tough, crisp, and 

 juicy, or soft and mealy. The chemical changes that take place in 

 fruit during ripening are very complex. Starch changes to sugar; 

 sugars change form; acids decrease; and soluble pectins increase in 

 the cell walls. These changes go on until the fruit becomes overripe 

 and unpalatable, with subsequent collapse. As these carbohydrate 

 constituents of the cell undergo ripening changes, oxygen is consumed 

 from the air, water and carbon dioxide are produced, volatile con- 

 stituents are given off, and heat is generated. All these activities are 

 embodied in what is spoken of as respiration. 



The chemical changes taking place in ripening fruit, and conse- 

 quently the rate of respiration, are retarded as the temperature is 

 lowered. The quicker heat is removed from fruit after picking to 

 bring it to an optimum storage temperature, the earlier the ripening 

 processes will be arrested and the longer the fruit can be kept. 



The generation of heat during the respiration and ripening proc- 

 esses, referred to in more detail on page 31, is greater than is com- 

 monly realized and is a factor deserving important consideration in 

 the design and operation of fruit cold-storage houses. The faster 

 a fruit ripens the greater the quantity of heat generated. A Bartlett 

 pear ripens faster than an apple at a given temperature, and, there- 

 fore, its greater heat of respiration results in larger refrigeration de- 

 mands, even when it is taken into storage at the same temperature as 

 the apple. Data on the generation of heat in apples and pears have 

 been discussed in an earlier publication (20). 



1 Italic numbers in parentheses refer to Literature Cited, p. 60. 



