When you take a sip of red wine or black tea, you’re swallowing a stiff swig of tannins. These astringent plant chemicals give the beverages their characteristic pucker. Now, the part of plant cells that makes and transports tannins — long overlooked by botanists — has at last been discovered, hiding right under our noses.

Tannins are a major way plants have of telling herbivores to graze elsewhere. They are deterrents because they denature — that is, deactivate — proteins. Humans have long taken advantage of this denaturing ability to “tan” animal skins with tannins, producing leather. The denaturation of the hide proteins by tannins renders them impervious to bacterial attack — otherwise known as rotting. In plants, tannins may also dissuade microbes and fungi from attacking and help protect plants from damaging UV.