Why does grape juice stain?

The color compounds in grape juice are called anthocyanins. These are large, heavy molecules that become deeply embedded in fabrics and other porous materials. When we touch something colored with grape juice, these molecules are transferred onto our skin and clothes, coloring them too.

Anthocyanins are also responsible for the deep purple and blue colors found in many fruits, vegetables, and flowers, including blueberries, blackberries, and eggplant.

Because anthocyanins are so large, they cannot easily be removed from fabrics. In fact, many types of fabric cannot be cleaned of anthocyanin stains at all.