Tannins, a group of bitter and astringent compounds, can be found abundantly in nature. They’re present in the wood, bark, leaves and fruit of plants as various as oak, rhubarb, tea, walnut, cranberry, cacao and grapes.

Perhaps most importantly, they’re also found in wine.

What do tannins do?

Plants have tannins to make themselves unpalatable. Their purpose in nature is to deter animals from eating a plant’s fruit or seeds before it’s ripe.

Tannins are responsible for that astringent, mouth-coating feeling you get from biting into an unripe pear or plum. Humans have used tannins from various tree barks for a long time to tan animal hides and make leather.