Fruit-based Life - Glossary of Terms

To hydrogenate a fat or oil means to add hydrogen atoms to carbon-carbon double bonds in unsaturated fatty acids, usually in the presence of a metal catalyst such as nickel. This reduces the number of double bonds and makes the fat more saturated, which can increase its melting point and make an oil more solid or stable at room temperature.

There are two important types:

Partial hydrogenation: Hydrogen is added to only some of the double bonds. This can cause some naturally cis double bonds to be converted into trans double bonds, producing trans fatty acids. Industrial partial hydrogenation was historically used to make products such as shortening and some margarines.
Full hydrogenation: Essentially all available double bonds are hydrogenated, producing highly saturated fatty acids and little or no trans fat from the hydrogenation process itself.

Hydrogenate (Food Chemistry Term)

Partial hydrogenation: Hydrogen is added to only some of the double bonds. This can cause some naturally cis double bonds to be converted into trans double bonds, producing trans fatty acids. Industrial partial hydrogenation was historically used to make products such as shortening and some margarines.
Full hydrogenation: Essentially all available double bonds are hydrogenated, producing highly saturated fatty acids and little or no trans fat from the hydrogenation process itself.