6 CIRCULAR 74 0, U. S. DEPARTMENT OF AGRICULTURE 



the fruit is reaching an advanced stage of ripeness and is a signal to 

 remove the apples that are approaching the end of their storage life. 

 Ethylene, a gas given off by ripe apples, pears, and some other 

 fruits, hastens the ripening of fruit stored at high temperatures, but 

 has very little effect at low temperatures. Even a very small quan- 

 tity of the gas will cause accelerated ripening at favorable temper- 

 atures. This is an added reason for designing the cold storage for the 

 rapid cooling of fruit in all parts of the rooms rather than attempt- 

 ing to provide for removal of the ethylene by ventilation. 



Controlled- Atmosphere, or Gas, Storage 



Reducing the oxygen content and regulating the concentration of 

 carbon dioxide in the atmosphere of a storage room generally slows 

 up the rate at which fruits ripen. This principle has been applied 

 as an auxiliary to refrigeration in the storage of some varieties of 

 apples and pears. Gas storage has come into considerable use in 

 England and to a limited extent in the northeastern part of the United 

 States, where certain varieties of apples are susceptible to low-tem- 

 perature disorders when stored in air at 32° F. 



The common practice is to seal the storage rooms until they are 

 essentially gasproof and permit the fruit to consume oxygen until it 

 reaches the desired level, thereafter controlling the concentration of 

 the gas by ventilation. The concentration of carbon dioxide is built 

 up to the desired percentage by the respiration of the fruit and there- 

 after is controlled, when necessary, by circulating the air through an 

 atmospheric washer containing a dilute solution of caustic soda to 

 absorb the excess carbon dioxide. Refrigeration equipment also is 

 necessary, since a temperature of about 40° is desired. 



The application of the principle of controlled-atmosphere to the 

 storage of fruits has been limited because of the varying tolerance to 

 carbon dioxide gas of different kinds of fruit. Likewise, different 

 varieties of apples respond differently to a given atmosphere of the 

 gases used. For detailed information on the use of controlled-atmos- 

 phere storage, see references to studies made in different localities in 

 the United States (i, 9, 22) . 



Storage Sanitation 



A storage interior free from decayed fruit, dirt, and mold is a 

 criterion of good management. The growth of surface molds within 

 a storage, however, may indicate favorable conditions of relative 

 humidity and does not particularly menace stored apples and pears 

 packed in closed containers. The use of fungicidal paints or the 

 annual whitewashing of walls, ceilings, posts, and air ducts and the 

 oiling of the floors will largely prevent the growth of surface molds, 

 which make them unsightly. Mold growth and spores may be killed 

 by spraying the empty storage with a sodium hypochlorite solution 

 having 0.8 percent available chlorine. The rooms should be closed 

 for a few days following the application. 



Chlorine vapor from a spray of sodium hypochlorite is an irritant to 

 the mucous membrane. Workmen should therefore be protected from 

 injury while spraying. This may be done by use either of fans to pro- 

 duce an air movement to carry away the fumes or of an all-service gas 

 mask in nonventilated rooms. 



