Biodiesel is produced from vegetable oils, yellow grease, used cooking oils, and animal fats. The production process, called transesterification, converts oils and fats into chemicals called long-chain mono alkyl esters, which is called biodiesel when used as a fuel. These chemicals are also referred to as fatty acid methyl esters or sometimes FAME. Roughly speaking, 100 pounds of oil or fat are reacted with 10 pounds of a short-chain alcohol (usually methanol) in the presence of a catalyst (usually sodium hydroxide [NaOH] or rarely, potassium hydroxide [KOH]) to form 100 pounds of biodiesel and 10 pounds of glycerin. Glycerin, which is used in pharmaceuticals and cosmetics, among other markets, is a co-product. Although the process is relatively simple, homemade biodiesel is not recommended. Users risk engine damage, loss of warranty, and operational problems from fuel that does not meet rigorous ASTM D6751 specifications.