Hydrogenation

hydrogenation or ‘hardening’ of fats, a process in which liquid oils are turned into solid fats, so that hard margarine can be made from vegetable or fish oils. The oils are heated in a container with hydrogen and a nickel catalyst, converting some of the unsaturated fatty acids to saturated ones, which are more solid (see fats and oils). Any possible health benefits from the original unsaturated fatty acids are lost.

The oils used to make soft margarine are not hydrogenated; instead, the spread is stiffened with emulsifiers (see emulsion).