Biodiesel begins with virgin vegetable oils (such as soybean, rapeseed, palm, or coconut oils), animal fats and fish oils, or recycled cooking oils. Manufacturers rely on a chemical reaction called "transesterification" in which they react the chemically acidic vegetable oils with methanol (a base) and add a catalyst. Fat molecules in the oil are broken into fatty acid methyl esters (FAME) or alkyl esters.