A crisp, sweet apple is highly desirable. It represents quality. However, given that apples are perishable, maintaining long term fruit quality is a challenge. An apple a day might maintain health, but how will those apples look six months from now? This is where science intervenes.
At harvest time fruit supply exceeds demand, but consumers still want high quality fruit at a later time. To maintain supply scientists developed post-harvest storage techniques. The most effective is controlled atmosphere storage. Controlled atmosphere combines cold temperatures, atmospheric gases and humidity to significantly reduce fruit spoilage and extend storage life. Reducing and maintaining cold temperatures is an older technology commonly found in home refrigeration. Maintaining atmospheric gas levels, primarily oxygen and carbon dioxide using nitrogen and carbon scrubbers, requires more complex equipment that is used in the industry. Humidity is maintained around 95%.
Apples are harvested based on optimum maturity indices, such as firmness or starch levels. The fruit is then sealed in an airtight storage facility room for at least six months and monitored for fruit quality. Temperatures are reduced and atmospheric gases are set and maintained at predetermined levels based on each apple variety. For example, Gala apples are best stored at 1.7% oxygen and 1.6% carbon dioxide. Past research has shown that fruit respiration rates are significantly reduced when oxygen and carbon dioxide gases are maintained at desirable levels over long periods of time. The ripening process is slowed and high fruit quality is maintained. This is desirable for both storage and supermarket operators because they can meet demand for high fruit quality at a later time.
Sources:
Best Apples.com, Washington Apples, Controlled Atmosphere Storage (CA)
Postharvest.UCDavis.edu, A Summary of Controlled and Modified Atmosphere Requirements for Apples
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