This project uses iodine spray to track how starch levels inside apples change at different storage temperatures. You cut apples in half horizontally and spray the exposed flesh with iodine solution. Darker color means more starch remains. As storage temperature rises — from 4 degrees C to 21 to 32 degrees C — apples ripen faster, and both starch and malic acid break down more quickly. That means the iodine color stays lighter in apples stored at higher temperatures.

Apples hold some of their stored energy as starch, and that starch breaks down as apples ripen. Warmer storage temperatures speed up ripening, so you can track the change by testing starch levels with iodine spray at different temperatures. As storage temperature rises, starch decreases — and the longer apples stay in storage, the more pronounced that drop becomes.

As apples ripen, their internal chemistry shifts — malic acid, the sharp flavor in a tart apple, breaks down alongside starch. Temperature drives this process. Apples stored at 32°C lose both malic acid and starch faster than those held at 21°C or 4°C, so the warmth of storage directly controls how quickly that tart sharpness fades and softness sets in.