TFS-158 - 18 - JANUARY I966 



CONTROLLED ATMOSPHERE STORAGE OF APPLES 



By Ben H. Pubols 

 Economic and Statistical Analysis Division 

 Economic Research Service 



Nature of Controlled Atmosphere Storag e 



Modification and control of the atmosphere in fruit storage plants is a 

 method used increasingly in recent years to hold the condition and extend the 

 storage life of fruit, especially apples. This is in addition to the main- 

 tenance of artificially cooled temperatures and high relative humidity, basis 

 requirements for regular cold storage. 



All fresh fruits continue to respire after harvest- -that is, they take 

 in oxygen and give off carbon dioxide. Many fruits, including apples, ripen 

 after harvest. This ripening process may be greatly retarded by the usual cold 

 storage methods, which reduce fruit metabolism including the rate of respiration. 

 Under controlled atmosphere (CA) methods, respiration and ripening may be reduced 

 further by lowering the oxygen content of the air, which normally consists of 

 21 percent oxygen, 78 percent nitrogen, and 1 percent other elements. 



Two principal techniques are employed to reduce the percentage of oxygen 

 in the apple storage rooms. The first involves the use of oxygen, and its 

 displacment by carbon dioxide, in natural respiration of the fruit. In this 

 process, however, provision must be made to prevent excess accumulation of carbon 

 dioxide, which could be harmful. The second method involves the circulation of 

 atmosphere of the desired composition (produced by commercial generators) through 

 the storage rooms to replace normal air. By this method the oxygen content may 

 be lowered sufficiently in a matter of hours, or at most a few days, much faster 

 than by the first method. 



Many fruits have been tested in CA storage to determine the most suitable 

 atmospheric conditions and temperatures for prolonging their life. They include 

 apples, pears, peaches, grapes, strawberries, bananas, and oranges. Results 

 have been most successful with apples. For apples in CA storage, levels of 2 to 

 3 percent oxygen and 1 to 7 percent carbon dioxide together with the appropriate 

 minimum temperature, usually 30 to 38 degrees (depending on the variety), and 

 95 percent relative humidity, are the most satisfactory for minimizing respira- 

 tion and the ripening process. Each apple variety differs slightly in 

 requirements for oxygen and carbon dioxide, temperature, and relative humidity 

 for optimum results. 



CA storage has been unusually successful with Mcintosh apples, allow- 

 ing storage for 7 to 8 months at 38 degrees F. When held under 38 degrees 

 in regular storage, Mcintosh are susceptible to internal breakdown, particu- 

 larly "brown core'. But at 38 degrees in CA storage, internal breakdown is 

 avoided and storage life is prolonged. Other varieties in regular storage 



