A chemical reaction, e.g. between an alcohol and a carboxylic acid, which produces esters. In the case of biofuel production, the esterification of animal or vegetable fats with alcohol is used. Reaction of vegetable fats with methanol (transesterification) creates fatty acid methyl esters, which is the main component of biodiesel. As a by-product, glycerine is produced, which can be used, for example, in the production of soap.