Providing year-round produce

There must be truth to the old English adage, “An apple a day keeps the doctor away.” Apples are the second most valuable fruit grown in the United States, with oranges being the first.

According to information from “Apples & More,” produced by the University of Illinois Extension, 2,500 varieties of apples are grown in the United States, with 100 of those grown commercially in 36 states.

Apple production has undergone many historical changes. Archeologists have found evidence that humans have been enjoying apples since at least 6500 B.C. History tells us that the apple tree originated in an area between the Caspian and Black Sea, and charred apples have been found in prehistoric dwellings in Switzerland. This fruit was also a favorite of the ancient Greeks and Romans. It is believed that the first U.S. apple trees were planted by the Pilgrims in the Massachusetts Bay Colony, and in colonial times apples were called winter banana or melt-in-the-mouth.

Although the fruit is grown in all 50 states, the top apple-producing states in 2006 were Washington, 58 percent; New York, 11 percent; Michigan, 8 percent; Pennsylvania, 5 percent; California, 4 percent; and Virginia, 2 percent. In 2005, there were 7,500 apple growers with orchards covering 379,000 acres.

Americans consume an estimated 16.7 pounds of fresh market apples annually, and one out of every four apples harvested in the United States is exported, approximately 24 percent, or 35.7 million bushels.

Methods of apple storage

Today’s methods of storage have come a long way since early growers packed apples in cellars and small fruit producers wrapped newspaper around each apple to prevent them from touching each other. Nesting apples in cartons of dry leaves was another way of making apples last throughout the winter.

Most consumers are unaware of the time lapse between when apples are picked and when they are available in stores. However, consumers demand crisp texture with firmness and a smooth, wrinkle-free peeling. Apples are ready for picking in the late summer through early fall. They must be kept in storage until ready for the market.

Because of the advent of a type of cold storage technology called controlled atmosphere (CA) storage, delicious, crisp apples are available year-round.

The atmosphere is comprised of 21 percent oxygen, 0.25 percent carbon dioxide, plus nitrogen and other minor gases. Apples are similar to people in that they breathe, taking in oxygen and releasing carbon dioxide. When conditions interfere with this process, ripening slows down.

Photo courtesy of USDA NRCS.
Apples, a major crop in Michigan, are available for consumer purchase throughout the year.

There are two methods to store apples used by the U.S. apple industry that ensure the best-quality apples are available any time of the year: regular, cold storage for short-term storage, and special, controlled atmosphere storage for longer storage.

Cold Storage: Each year, growers pick apples at just the right time in the ripening cycle, when they are firm, but aren’t sour or starchy. The apples are rushed to cold storage warehouses, consisting of large refrigerated storerooms, where the temperature is kept at 32 degrees Fahrenheit and high humidity is maintained. The cold temperature slows down, but does not stop, the ripening process. Most apples put in regular cold storage are sold by late January or early February.

Controlled Atmosphere Storage: In 1940, Dr. Robert Smock of Cornell University experimented with reducing oxygen and increasing carbon dioxide in storage facilities, resulting in the development of controlled atmosphere, or CA, storage. CA storage requires airtight, refrigerated warehouse rooms that are sealed after the apples are placed inside. The oxygen content is reduced from 21 percent to 2.5 percent, and the carbon dioxide level is increased from 0.25 to 2 to 5 percent, and high humidity is maintained.

Using the CA process, ripening is reduced. As the CA method is more costly per bushel, only the highest-grade apples are placed in this type of storage. After the first of the year, storage rooms using CA methods are opened and converted to regular cold storage. Supply and demand determine the duration of time this requires.

Tom Papke, a Washington shipper with a background in CA methods, says, “The CA storage method is like apples are hibernating or being put to sleep. A minimum of 60 days is recommended. The best apples for storage are the Red Delicious and Granny Smith, which are available year-round. Galas have a short shelf life and are usually picked in August. Even under the best conditions, refrigeration can’t stop all aging and spoilage.”

Papke explains a new technology in apple storage known as SmartFresh, which helps apples maintain their fresh-picked qualities, including crunch, taste and juice content. Introduced in the United States in 2002, the method was used in a limited amount in Chile and Argentina. Researchers developed the technology, and a company called AgroFresh, Inc. acquired the technology for development in 1999. Universities and institutes around the world have been working with AgroFresh to further the technology.

The method works by storing apples in a large refrigerated room with special controlled atmospheres to counter spoilage. SmartFresh is added to the air to slow the ripening process so that the qualities associated with fresh-picked apples can be maintained. This product is a one-time, 24-hour application at the beginning of storage. When the fruit is removed from storage, it slowly begins ripening again.

SmartFresh works with the natural ripening process by making the fruit less susceptible to the damaging effects of ethylene. Ethylene, a naturally occurring plant substance, is key to ripening, aging and eventual spoilage of fresh produce. Apples produce ethylene and are sensitive to it. Keeping ethylene as low as possible maintains harvest quality for consumers.

Health and safety concerns

Known for their health benefits, apples are an excellent source of antioxidants. Research teams from Oregon State University in conjunction with the Linus Pauling Institute have shown that apples stored with SmartFresh maintained the important levels of antioxidants that are seen in apples coming from today’s storage conditions.

With recent emphasis on safety of food products, SmartFresh delivers a safety profile expected in today’s safety-conscious environment:

  • No detectable residues on apples. (Residues, if any, are so low they are at non-detectable levels.)
  • Hundreds of times safer than the level normally required by regulatory agencies worldwide.
  • Eliminates the need for a residual postharvest treatment used to control a common apple storage disorder.
  • Works in a nontoxic way.
  • Has no effect on the environment. Water used to dissolve the products does not generate any hazardous waste.
  • Safe to beneficial insects and to aquatic species.
  • Safe for apple storage facility operator. Also, packaged in a time-delayed application system.
  • Not part of the traditional class or crop protection treatments.
  • Works with the natural ripening process, it uses no genetic engineering or biotechnology.

The research and commercial use of CA storage for apples continues to be improved. The correct combination of oxygen, carbon dioxide, temperature and humidity for each variety can still be improved as new varieties such as Fuji, Gala, Braeburn and Jonagold take their place in the market.

Carolyn R. Tomlin writes from Jackson, Tenn.