Fermentation in food processing is the conversion of carbohydrates to alcohols and carbon dioxide or organic acids using yeasts, bacteria, or a combination thereof, under anaerobic conditions. Fermentation usually implies that the action of microorganisms is desirable. The science of fermentation is also known as zymology or zymurgy. The term “fermentation” is sometimes used to specifically refer to the chemical conversion of sugars into ethanol, a process which is used to produce alcoholic beverages such as wine, beer, and cider. Fermentation is also employed in the leavening of bread (CO2 produced by yeast activity); in preservation techniques to produce lactic acid in sour foods such as sauerkraut, dry sausages, kimchi, and yogurt; and in pickling of foods with vinegar (acetic acid). Natural fermentation precedes human history. Since ancient times, however, humans have been controlling the fermentation process. The earliest evidence of an alcoholic beverage, made from fruit, rice, and honey, dates from 7000–6600 BCE, in the Neolithic Chinese village of Jiahu, and winemaking dates from 6000 BCE, in Georgia, in the Caucasus area. Seven-thousand-year-old jars containing the remains of wine, now on display at the University of Pennsylvania, were excavated in the Zagros Mountains in Iran. There is strong evidence that people were fermenting beverages in Babylon circa 3000 BC, ancient Egypt circa 3150 BC, pre-Hispanic Mexico circa 2000 BC, and Sudan circa 1500 BC. French chemist Louis Pasteur was the first known zymologist, when in 1856 he connected yeast to fermentation. Pasteur originally defined fermentation as “respiration without air”. Pasteur performed careful research and concluded:
