The only alcohol suitable for drinking is ethyl alcohol, a liquid produced by distilling the fermented juice of fruits or grains. Pure ethyl alcohol is clear, flammable and caustic. Water is therefore added to reduce its potency. In the United States, the average amount of alcohol in distilled spirits is about 40 percent (80 proof). Pure alcohol boils at 173°F, water at 212°F. A mixture of the two will boil somewhere between these two temperatures. A USDA study has disproved the theory that alcohol evaporates completely when heated. In truth, cooked food can retain from 5 to 85 percent of the original alcohol, depending on various factors such as how and at what temperature the food was heated, the cooking time and the alcohol source. Even the smallest trace of alcohol may be a problem for alcoholics and those with alcohol-related illnesses. Because alcohol freezes at a much lower temperature than water, the amount of alcohol used in a frozen dessert (such as ice cream) must be carefully regulated or the dessert won't freeze. Calorie-wise, a one-and-a-half-ounce jigger of 80-proof liquor (such as Scotch or vodka) equals almost 100 calories, a four-ounce glass of dry wine costs in the area of 85 to 90 calories and a twelve-ounce regular (not light) beer contributes about 150 calories.