An important chemical in wine, beer, and hard liquor, ethyl alcohol is a natural substance derived from the fermentation of yeast and sugar. Insofar as it contains calories, ethyl alcohol is a food, but since it affects the central nervous system, it is also a drug. Its presence in alcoholic beverages ranges from a low of 4% (eight proof) in most beers to more than 50% (100 proof plus) in hard liquors. The higher the proof, the higher the calories and the greater the effect on the central nervous system.