Malic acid gives a tart apple its sharp flavor, and as apples ripen it gradually breaks down. To track that decline precisely, a titrator adds reagent drop by drop to juiced samples until the reaction endpoint is reached — the exact amount of malic acid in each sample becomes measurable. Red Delicious apples stored at 4°C, 21°C, and 32°C are juiced at regular intervals, and the titrator measures how malic acid shifts across each temperature group. Starch levels get a parallel check with iodine spray. As storage temperature rises, both compounds decrease — and the longer the apples stay in storage, the steeper that decline.

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.

Starch is a type of sugar that plants make to store energy, and apples hold some of that stored energy as starch. As apples ripen in warmer conditions, that starch breaks down — along with malic acid, the sharp flavor in a tart apple. By testing starch levels with iodine spray at storage temperatures of 4, 21, and 32 degrees C, you can track how both compounds decrease as temperature rises and storage time lengthens.

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.