Vitamin C — also called ascorbic acid — breaks down when juice is heated or processed. That means fresh-squeezed orange juice typically holds more of this nutrient than bottled juice that has sat on a shelf. To measure how much remains, you add drops of juice one at a time to a vitamin C indicator solution that starts blue. When the blue color disappears, you stop counting. Fewer drops means a higher concentration of ascorbic acid in that juice. Testing fresh-squeezed, bottled, frozen, and canned juice — three times each — lets you compare the average drop counts and determine which type preserves the most.

When tomatoes and cherries are cooked, the heat changes how much ascorbic acid remains in the fruit. To see exactly how much, you prepare an iodine-starch solution that turns dark purple. Adding drops of a blended fruit sample causes that purple color to fade — the more it fades, the more vitamin C is present. You blend each fruit with water, split it into two samples, and heat one on a hot plate while leaving the other raw. Comparing the color changes between cooked and raw samples reveals whether cooking destroys the vitamin C or, as some results suggest, concentrates it.