Alcohol strength comes from ethanol concentration, and this value appears as Alcohol by Volume which defines how strong the drink feels in use. This measure shows how many millilitres of ethanol exist inside 100 millilitres of liquid at 20°C in an exact calculation. In the United States, the Alcohol and Tobacco Tax and Trade Bureau controls how these values are defined and displayed on products with strict rules. Yeast used in brewing stops working once ethanol reaches between 14% and 18%, forcing producers to apply distillation for higher levels. For stable production, companies often depend on food grade ethanol manufacturers Alabama to maintain chemical balance in base spirit materials.