Crunchy, munchy U.S. apples are available year−round because of the advent of a type of cold storage technology called controlled atmosphere storage.
Our atmosphere is 21% oxygen, 0.25% carbon dioxide, plus nitrogen and other minor gases. Like humans, apples breathe (aka ripening!), and thus depend on oxygen and release carbon dioxide. Any interference with and/or slowing of the intake of oxygen will slow down the apples´ natural ripening process. This is where the high−tech science of storing apples comes in!
The U.S. apple industry uses two types of storage technology to ensure that you receive the best−quality apples at any time of year: regular, cold storage for short−term storage, and special, controlled atmosphere storage for longer storage.
Cold Storage: Each year, growers pick their apples at just the right time in their ripening cycle, when they are firm and will hold over a period of time, but aren´t sour or starchy. The apples are then rushed to cold storage warehouses, consisting of large refrigerated storerooms, where the temperature is kept at 32 degrees and high humidity is maintained. This cold temperature slows down but does not stop the ripening process. Hence, most apples put in regular cold storage are sold by late January or early February. Regular cold storage is less expensive than controlled atmosphere storage.
Controlled Atmosphere Storage: Remembering that apples take in oxygen and give off carbon dioxide, in 1940 Dr. Robert Smock of Cornell University experimented with reducing oxygen and increasing carbon dioxide in storage facilities, resulting in the development of a new storage technology called controlled atmosphere (CA) storage. CA storage requires air−tight, refrigerated warehouse rooms that are sealed after the apples are placed inside. The oxygen content in the storeroom air is reduced from 21% to 2.5%, and the carbon dioxide level is increased from 0.25% to 2−5%, and high humidity is maintained.
The CA process radically reduces the ripening process, thus allowing us to provide great−tasting U.S. apples year−round. Since CA storage is more costly per bushel, only the very best apples are put into this type of storage. CA storages are opened and converted to regular cold storage rooms usually after the first of the year, depending on demand and supply conditions.
(December 27, 2001)