Agriculture Reference
In-Depth Information
A simple and reliable method that has long been used by commercial
growers is the iodine test. As apples form and grow, they are first composed
mostly of starch. As they mature, the starch is converted to sugar. Iodine re-
acts with starch to form a blue color, but it does not react with sugar. To
use this method, collect several apples of each variety. Cut the apples in half
to obtain a cross section perpendicular to the stem. Spray a standard iod-
ine solution, available from orchard supply companies, on the cut surface.
Starchy areas will appear blue. Areas that have converted to sugar remain
yellowish-white. Rate your apples by comparing the staining pattern with
pictures on standardized charts that are available for popular varieties.
Typical ratings range from 1.0 (immature) to 6.0 (fully ripe), although dif-
ferent systems have ranges of 1 to 9. Although the scale differs somewhat
between apple varieties, ratings of about 2.0 to 2.5 indicate the time to har-
vest for long-term controlled atmosphere storage. Ratings of about 3.0 to 4.0
indicate the time for long-term refrigerated storage. Ratings of 4.5 to 6.0 in-
dicate the fruit is ready to eat. Start making your iodine tests twice weekly
beginning 2 weeks before your expected harvest date, based on days from
'Liberty' apples.
