Controlled Atmosphere Storage

The process known as 'controlled atmosphere storage ', or "CA" for short, has been utilized for much of the last century. Shortly before World War II, farmers in England discovered that their produce kept longer when stored in an airtight room. With information gleaned from years of scientific research and with advances in modern technology, CA storage now includes a number of specified steps and specialized conditions. This is a non-chemical process which carefully monitors temperature, oxygen levels, carbon dioxide and humidity.

How does CA help keep apples fresh? Apples take in oxygen and give off carbon dioxide as the starches in their flesh change to sugar. When this so-called respiratory process occurs in sealed storage, the available oxygen is reduced, thus retarding the apple's natural ripening process. An infusion of nitrogen gas reduces the oxygen levels in these sealed rooms, lowering it from roughly twenty percent (found in the air we breathe) to a mere one-to-two percent. Temperatures are kept at slightly above freezing--between 32 and 36 degrees--and the humidity is sustained at 95 percent. Carbon dioxide gradation is also regulated. Precise conditions in these CA rooms are set according to each individual apple variety.

Because researchers in Washington state have been at the forefront of this industry for well over thirty years, a definitive configuration for each variety has now been developed. This ensures that the apples grown in every orchard in the state attain their highest and best quality. Washington currently provides accommodation for the largest volume of CA storage found in any growing region in the world.

These vast, airtight rooms hold anywhere from ten thousand to one hundred thousand boxes, depending upon the individual grower/shipper and his marketing resources. Growers begin testing for optimum conditions in their orchards around mid-August. They need to accurately gage the right time for harvest, which is crucial to successful storage results. Neither those apples which are picked too early nor those just past maturity will keep well, even under CA conditions. The crop yield needs to be mature but not too ripe, so growers test for a variety of components, such as the fruit's skin colour, seed colour, sugar level and flesh chlorophyll. After the fall harvest (and 'fresh-eating' season), much of Washington's apple crop is shipped to market. Since most apple varieties will keep for a full twelve months in CA storage, fruit packers and shippers maintain their businesses year-round, with the bulk of the product being shipped between the months of January and September.