Michigan State University Extension
Preserving Food Safely - 01600656
Late maturing varieties of apples will store for use throughout the winter if the fruit is hard, mature and in perfect condition. Apples picked too green are subject to a number of storage disorders, such as scald and bitter pit; if picked beyond maturity, they quickly become overripe in storage.
Cool as quickly as possible after harvest for best results. For most varieties of apples, the optimum storage temperature is 30 to 32 degrees Fahrenheit with a 90% relative humidity. Higher storage temperatures reduce the storage life considerably, and apples ripen twice as fast at 40 degrees Fahrenheit as at 32 degrees Fahrenheit.
Apples can be stored outdoors in insulated boxes or straw-lined pits or buried containers as long as the outside temperatures are above 10 degrees Fahrenheit. They will last longer and retain more flavor if kept in a fruit cellar in plastic bags or in cardboard boxes lined with plastic sheets. However, the cardboard box and plastic bags or liners must be perforated to allow air circulation. If the fruits are individually wrapped in tissue paper or newspaper before being placed in boxes or baskets, better results will be achieved. Plastic liners help maintain high humidity and prevent the apples from being affected by the surrounding air. The balance of humidity is subtle; excess humidity will encourage decay, and insufficient humidity will encourage shriveling.
Avoid storing apples too long and regularly check for signs of spoilage. Mustiness will spread to healthy specimens. Storage duration depends on the variety.