Potatoes are mostly water, which is why they lose weight when baked for a long time.

The longer version

A raw potato is roughly three-quarters water by weight, held inside cells whose starch granules also contain some moisture. In a hot oven, water at the surface evaporates first, and then moisture from the interior migrates outward and escapes as vapor, so the whole tuber steadily loses mass.

Starch granules gelatinize as they take up what water remains, which is what turns dense raw flesh into a fluffy interior. The skin acts as a barrier, so a potato baked whole loses water more slowly than one that has been cut open. Varieties differ in starch content, which changes how dry the finished flesh feels.

Where this entry sits

Everyday ingredients turn out to be full of quiet chemistry and long history. This collection gathers short, plain explanations of how bread rises, why onions sting, where common spices originate, and how coffee, tea, and chocolate reached the modern kitchen. The full list sits on the Food and Drink page, where every entry is listed in order.