Acetic acid is the colorless, pungent-smelling weak acid responsible for vinegar's sour taste and much of its preservative power. It forms naturally when ethanol is fermented by acetic acid bacteria, a process used for centuries to turn wine, cider, or rice wine into vinegar. In the kitchen, acetic acid (as vinegar) is used to add tang, balance rich or sweet flavors, and preserve foods such as pickles and chutneys, since its low pH inhibits the growth of bacteria, mold, and yeast. It is also produced synthetically for use as a food additive with the same preservative and flavoring purposes; small amounts occur naturally in some fermented products, including wine, beer, and kombucha, typically as an unwanted spoilage byproduct rather than an intended flavor.