Biodiesel is made by chemically converting any animal fat or vegetable oil into a less viscous product through a process called transesterification. The fat or oil is refined so that there is no water or solids present, then it is vigorously mixed with an alcohol (usually methanol) and a catalyst (potassium hydroxide, also known as lye) to cause the fat or oil to separate into two distinct layers. Glycerin settles to the bottom where it is drained off and purified into a substance that is useful for many applications. The biodiesel layer that remains is put through a thorough purification process and then tested to ensure that it meets all of the ASTM-6571 specifications. One gallon of fat or oil typically becomes about 1 gallon of biodiesel, and the 0.2 gallons of methanol typically becomes about 0.2 gallons of glycerin.