A Technical Information Bulletin
Northwest Horticultural Council
Controlled Atmosphere Storage
Eating crisp, juicy apples year-round from Pacific Northwest orchards is possible due to controlled atmosphere storage. Known simply as “CA storage” in the produce business, controlled atmosphere storage involves careful control of temperature, oxygen, carbon dioxide and humidity.
Prior to the development of modern refrigerated storage, apples were stored in cellars, pits, caves or barrels. When stored at cool, consistent temperatures, apples could be stored for three to four months, but suffered high levels of dehydration and loss of nutrients. In the early 20th century, farmers in England observed that produce stored better, and longer, when stored in an airtight room. These observations eventually led to the development of controlled atmosphere storage, as scientists conducted detailed studies of the apple and ripening processes, laying the groundwork for modern storage techniques.
Like humans, apples “breathe”, taking in oxygen and releasing carbon dioxide as the fruit matures. A reduction in the amount of oxygen available reduces the rate of respiration, slows down the natural ripening process, and extends the storage life of the fruit.
CA storage is a non-chemical process. Oxygen levels in the sealed rooms are reduced from the ambient concentration of approximately 21 percent to 1 or 2 percent. Temperatures are maintained between 32 and 36 degrees Fahrenheit. Humidity and carbon dioxide levels are also controlled according to specifications for each apple variety. Researchers continue to study and develop specific storage regimes for each variety and crop to achieve the best quality.
Controlled atmosphere storage has come a long way since the first commercial CA rooms in California in the early 1950s. While most popular for storage of apples and pears, CA is used worldwide, and for other commodities as well, including bananas, kiwi fruit, melons and strawberries. Washington state has the largest capacity of CA storage of any growing region in the world.
When proper growing and harvesting techniques are used, many varieties of apple can store for 12 months or longer in CA. Most of these apples are shipped to market between January and September. Regular refrigerated storage is used for much of the fruit marketed in the fall, soon after harvest, and in the early winter months.
What is CA storage?
Controlled atmosphere storage is a system in which fresh, perishable products (such as fruit and vegetables) are stored under environmental conditions that extend the shelf life after harvest. In the past 50 years, controlled atmosphere storage has become a staple of the world-wide fruit industry and makes it possible for fresh, high quality fruit to be available year-round.
Does the use of CA storage affect the safety of the fruit?
Controlled atmosphere storage is a non-chemical process that does not affect the safety of fruit. The reduced oxygen levels reduce respiration rate and slow the ripening process naturally.
The Northwest Horticultural Council represents the deciduous tree fruit industry of Idaho, Oregon and Washington on national and international policy issues affecting growers and shippers. For further information, please contact the Northwest Horticultural Council at 509-453-3193.