There was no need to invent vinegar as it makes itself without difficulties. When wine or any alcoholic drink is exposed to the air it turns sour. Aerobic (air-breathing) bacteria invade it and oxidize (combine with oxygen) the alcohol to acetic acid. Before the invention of the wine cork this was a constant and unwelcome phenomenon. Flasks of wine were sealed with clay and wax which often cracked and let in the air, so that the wine soon went sour. Indeed the word ‘vinegar’ comes from the French vin aigre, meaning sour wine.