Michigan is one of the leading apple producing states.  For many years MSU has tested apple maturity as harvest approaches to allow growers and shippers to make informed decisions on harvest dates and marketing for the many apple varieties grown in Michigan.   MSUE District Fruit Agents collect samples from area orchards and either test the apples themselves or send the samples to Dr. Randy Beaudry’s post harvest physiology lab in the MSU Department of Horticulture. Apples are sampled for flesh firmness, starch content (the conversion of starch to sugar), soluble solids (sweetness of the juice), and ethylene content of the fruit. 

Predicted 2007 Apple Harvest Dates by Phil Schwallier

The 2007 Apple reports are finished

Regional Apple Maturity Reports.

Southwest Michigan Apple Maturity Reports are posted at the SWMREC site

Southeast Michigan Apple Maturity Reports are also posted at the SWMREC site

Grand Rapids Area Apple Maturity Reports are posted here
Last report 10/4/2007

Oceana and Ludington Area Apple Maturity Reports are posted here
Last report 9/26/2007

Northwest Michigan Apple Maturity Report  are posted at the NW Michigan Station

Predicted Apple Harvest Dates by Phil Schwallier

Predicted 2006 Apple Harvest Dates by Phil Schwallier

Predicted 2005 Apple Harvest Dates by Phil Schwallier

Some of the parameters reported in Apple Maturity Reports

Soluble Solids

Measured with a refractometer, is a measure of the sweetness of the fruit are measured in Brix.
The higher the Brix, the sweeter the fruit.

Flesh Firmness or Pressure

Measured with a pressure tester, is a measure fruit firmness or crispness. It is measured in pounds.
The higher the pressure the harder the fruit.
Varieties can vary widely in pressure. All varieties lose pressure as they ripen.

Starch Removal

Measured with a Starch-Iodine test,
Fruit are cut in half and the exposed surface is placed in a solution containing Iodine, which stains starch black.
As the apple ripens starch in the flesh is converted to sugars increasing the soluble solids.
Low numbers indict lots of starch. Apples for long term storage are harvested when the starch removal score is 3 to 4. Ripe fruit ready to eat, too ripe for long term storage will score between 5 and 7.

Skin color

Is estimated as the percentage of the skin that is colored, i.e. red.

Ground color

Is the background color of the skin. It often changes from green to yellow as apples ripen.

Ethylene content

Measured with a gas chromatograph.
Apples begin to produce ethylene as they ripen, a large surge of ethylene indicates that the final ripening process has begun and the fruit are too ripe for storage and are ready to eat.

Other Fruit Maturity Information

Apple Maturity Guide

Suggested maturity levels for different apple varieties, and storage windows.

Effects of Cold on Apple Maturity

Cold and frosty conditions will increase the pace of apple maturation. Cold conditions near 24°F to 26°F will cause apples to start producing ethylene and will start dropping in 10 days or so. Stop drop usually does not work well on apples that experience a hard freeze. Higher elevations will have warmer conditions then the frost pockets. Lightly frosted apples at 28°F or higher seem to ripen in a normal pattern. Apples that experience multiple light frost, like we have had recently, may have a hastened maturity.

Other Michigan Apple Web Resources

The Michigan Apple Committee maintains an excellent web site for consumers with links to Michigan apple shippers, listings of Cider Mills, farms with road side sales, and all kinds of information on apples. 

Also see the Apple Page at this Fruit Team Website

Apple Scab Resistant varieties are rare in the grocery store but promise fewer sprays for the backyard grower.

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