Hydrogenation, the chemical reduction of organic compounds through the addition of hydrogen molecules. Hydrogenation is most commonly used in solidifying vegetable oils to make margarine and solid shortenings. The process is also used in the production of certain liquid fuels and lubricants, and in making various chemicals.

In hydrogenation of fats, molecular hydrogen is added to an oil compound in the presence of a catalyst, a substance that speeds the chemical action. The components are agitated under high pressure at temperatures ranging from 350 to 400 F. (177 to 204 C.) until the hydrogen unites with the molecules of oil. The resulting compound changes its state from liquid to solid, the catalyst (usually nickel powder) is screened off, and the solid fat is cooled.