Pour the iodine solution into a shallow glass container to a depth of 5 to 7.5 mm (approx. 1/4 inch). Cut each apple in half horizontally across the core and put the exposed surface of one of the halves in the iodine solution. The apple stem can serve as a convenient handle, if the top half is used.
Wait 1 minute before removing the apple half. Repeat with the next test apple.
Compare the patterns of black spots, which indicate the presence of starch.
When there is no reaction and no color change, all of the starch has changed to sugar.