The reaction in which acids and alcohols combine to form esters. It can be catalysed enzymatically by esterases or chemically by mineral acids. In food chemistry it creates many of the fruity aroma compounds in fermented beverages and ripened products, and it is used to modify fats and emulsifiers. Fischer esterification under acid catalysis is reversible, so removing water drives it toward the ester; enzymatic routes with lipases in low-water media achieve the same transformation selectively. Food applications include synthesising flavour esters such as ethyl butyrate and isoamyl acetate, and producing emulsifiers like diacetyl tartaric esters of monoglycerides (DATEM).