If you’ve ever revisited an opened bottle of wine left out too long, you may notice it’s slightly brown and smells a little off, like vinegar. Such are the destructive effects of oxidation—the same process that turns a cut apple brown or causes an avocado’s color to change. Oxidation happens when a wine’s exposure to air triggers a series of chemical reactions that convert ethanol (what we commonly refer to as alcohol) into acetaldehyde. Some oxygen exposure can be beneficial to wine, but too much will cause its flavors to go flat and ruin its taste, turning it to vinegar. In the latter situation, you would consider the wine "oxidized".