Snapshot of History of CA storage: 
- BC - Egyptians store in limestone crypts
- 1918 - Kidd & West in Cambridge UK
- 1929 - 1st commercial use in UK
- 1938 - Smock in Cornell NY USA
- 1965 - Low Oxygen apple storage (2%)
- 1978 - Ultra low Oxygen apple storage (1.2%)
CA storage as we know it got its start in England before World War II when farmers discovered their produce kept longer if stored in an airtight room. It was up to scientists to unravel the reasons for longer storage.
Buying crisp, sweet fruit year-round is possible due to controlled atmosphere storage. Controlled atmosphere "CA" storage involves careful control of temperature, gases (oxygen, carbon dioxide and nitrogen) and humidity; all kept at specified levels.
Apples take in oxygen and give off carbon dioxide as starches in the flesh change to sugar. In sealed CA rooms, this respiratory process reduces the oxygen level to slow the ripening process.
CA storage has come a long way over the years. Researchers in Washington state have been among the leaders in this technology. CA was first used commercially in the United States in the 1960s and Washington now has the largest capacity of CA storage of any growing region in the world.
Stemilt's airtight CA rooms vary in size from 16,000 carton capacity (800 bins) to 60,000 carton capacity (3000 bins). Stemilt uses smaller CA rooms to maintain "Rapid CA". Smaller CA rooms allow fruit to be loaded more rapidly and get fruit under CA soon after harvest. Smaller CA rooms also offer more flexibility and improved market timing.
CA storage is a non-chemical process. Oxygen levels in the sealed rooms are reduced, usually by the infusion of nitrogen gas. Oxygen levels drop from approximately 21 percent in the air we breathe to 1 percent or 2 percent. Temperatures are kept at a constant 32 to 36 degrees Fahrenheit. Humidity is maintained at 95 percent and carbon dioxide levels are also controlled. Exact conditions in the rooms are set according to the fruit variety. Researchers develop specific regimens for each variety to achieve the best quality. Computers help keep conditions constant.
Timing of harvest is critical to good storage results. Fruit picked too early will not store well in CA nor will those that are past the proper maturity.
In mid-August, apple growers start testing the maturity of their apples to accurately predict when to harvest their crop to put in CA rooms so the apples are mature, but not too ripe. Pear growers soon follow with similar tests. Firmness, skin color, seed color, sugar level and flesh chlorophyll are tested.
When the proper growing and harvesting techniques are used, many varieties of apples 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 and early winter months.
Stemilt and all our CA rooms are licensed and certified by the Washington State Department of Agriculture.
Washington law places requirements on the length of time fruit must remain in CA conditions to qualify as CA-certified. Then state inspectors check every lot of fruit as the lot comes off the packing line to make sure the apples meet maturity requirements, the same requirements the U.S. Department of Agriculture uses for apples being exported. Only then will the carton be stamped with the warehouse number and the "CA" symbol.
Fruit meeting these standards must be shipped within two weeks or be re-inspected to meet the same requirements. If they don’t pass, the CA designation cannot be stamped on the carton. These standards apply to all apples shipped under Washington Extra Fancy and Washington Fancy grades and all US No. 1 grade pears.
Washington has the highest concentration of CA storage of any growing region in the world.