Vinegar is a combination of acetic acid and water made by a two-step fermentation process. First, yeast feed on the sugar or starch of any liquid from a plant food such as fruits, whole grains, potatoes, or rice. This liquid ferments into alcohol. It is used as a condiment to add flavor or as a preservative, as in pickling. Vinegar contributes acidic notes to foods, both in aroma and taste.