Controlled atmosphere

A controlled atmosphere is an agricultural storage method. An atmosphere in which oxygen, carbon dioxide and nitrogen concentrations as well as temperature and humidity are regulated.

Two major classes of commodity can be stored in controlled atmosphere:

1. Dry commodities such as grains, legumes and oilseed. In these commodities the primary aim of the atmosphere is usually to control insect pests. Most insects cannot exist indefinitely without oxygen or in conditions of raised (greater than approximately 30%) carbon dioxide. Controlled atmosphere treatments of grains can be a fairly slow process taking up to several weeks at lower temperatures (less than 15°C). A typical schedule for complete disinfestation of dry grain (<13% moisture content) at about 25°C, with carbon dioxide, is a concentration above 35%(v/v) carbon dioxide (in air) for at least 15 days.^[1] These atmospheres can be created either by:
   • adding pure gases carbon dioxide or nitrogen or the low oxygen exhaust of hydrocarbon combustion, or
   • using the natural effects of respiration (grain, moulds or insects) to reduce oxygen and increase carbon dioxide Hermetic storage.^[2]
2. Fresh fruits, most commonly apples and pears, where the combination of altered atmospheric conditions and reduced temperature allow prolonged storage with only a slow loss of quality.

See also

• Modified atmosphere
• Modified atmosphere/modified humidity packaging
• Shelf life
• Cold chain

References

1. ^ Annis, P.C. and Morton, R. 1997.The acute mortality effects of carbon dioxide on various life stages of Sitophilus oryzae. J. Stored Prod.Res. 33. 115-124
2. ^ Annis P.C. and Banks H.J. 1993. Is hermetic storage of grains feasible in modern agricultural systems? In “Pest control and sustainable agriculture” Eds S.A. Corey, D.J. Dall and W.M. Milne. CSIRO, Australia. 479-482.