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Friday, Apr. 29, 2016

Extention Line

Wednesday, September 21, 2011

This week, we bring you some good information about apple harvest and storage from Paul Domoto, ISU Extension Fruit Specialist:

The cool temperatures we have been experiencing are optimum for promoting red color in apples. The red color comes from anthocyanin pigments in the skin that are enhanced by good exposure to sunlight and cool night temperatures that drop into the lower 50's and 40's. However, with the early red color development, don't be fooled into thinking the apples have reached proper maturity. Although the red color develops as the fruit mature, it is a poor indicator of maturity, particularly with the high-color stains available in some varieties. For this reason, the background color, as it changes from green to a shade of yellow is a better indicator of fruit maturity. Another method for testing maturity is by taste. At harvest maturity, the apples will still be "starchy", but there will be some sweetness and the characteristic varietal flavor will be detectable.

Because apples accumulate starch during the growing season, and the starch begins to convert to sugars at the onset of fruit maturation, probably the most reliable method of testing fruit maturity is the starch-iodine test. This conversion of starch to sugar begins in the core, and progresses outward toward the skin. When the starch disappears in the core and the disappearance begins to radiate out into the flesh, the fruit have reached minimum maturity for a quality product. Optimum maturity is reached when the starch disappears in about half of the flesh and fruit are considered over-mature when there is no starch remaining in the flesh.

Apples that have reached minimum maturity will store the longest, while those that are more mature should be marketed as soon as possible while they are still crisp. Therefore, for each variety, a first-in, last-out approach to marketing should be taken; fruit harvested first should be the last fruit to be marketed.

Honeycrisp is a variety that is susceptible to soft scald when stored for over two months. Other susceptible cultivars include 'McIntosh', 'Jonathan', 'Wealthy' and 'Rome'. Soft scald is characterized by patches and ribbon-like areas of brownish skin with a distinct line separating healthy and injured tissue. It can affect just the skin or extend into the flesh. When the flesh is affected, it becomes water-soaked and brownish in color (referred to as "soggy breakdown"). Affected areas are prone to secondary infections. Soft scald is induced by the exposure of mature fruit or late-harvested fruits to storage temperatures bordering on the freezing point of apples.

Soft scald on Honeycrisp apples can be reduced by:

* Avoid harvesting over-mature fruit. Harvesting at a starch-index of 5 to 6 has been shown to reduce the incidence of soft scald.

* Storing fruit between 36 to 38 degrees F.

* Subject the fruit to a one-week delay at about 50 degrees F before moving them into cold storage. This treatment effectively reduced soft scald on 'Honeycrisp' even when the fruit were stored at 33 degrees F, but increased the incidence of bitter pit.

* DPA post-harvest dip: Was effective in reducing the incidence of soft scald when the fruit were stored at 37 degrees F, but not at 33 degrees F.

For more information about apple varieties and cooking or eating them, stop by the Cherokee County Extension Office at 209 Centennial, Suite A Cherokee Iowa. If you would like to call us, our phone number is 225-6196, we also have email; xcherokee@iastate.edu.