A Technical Information Bulletin
of the
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, humidity, oxygen, and carbon dioxide concentrations.
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 ripening process, laying the groundwork for modern storage techniques.
Like humans, apples “breathe”, taking in oxygen and releasing carbon dioxide as the fruit matures. This process is called respiration. 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 as low as one percent, depending on apple variety. Temperatures are maintained between 32 and 34 degrees Fahrenheit. Humidity and carbon dioxide levels are also controlled according to specifications for each variety. Researchers continue to study and develop specific storage regimes for different varieties and growing regions to achieve the best quality fruit.
CA storage has come a long way since the first commercial CA rooms were installed 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. The most advanced CA systems are able to dynamically sense fruit responses to low oxygen, and are called Dynamic CA or DCA.
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.
Common Questions:
What is CA storage?
CA 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. Over the past 50 years, CA storage has become a staple of the worldwide 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?
CA 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, contact the NHC at 509-453-3193.
Updated 2/6/2023
