How does hydrogenation change liquid vegetable oils into more solid fats?

Hydrogenation is a chemical process used to convert liquid vegetable oils into more solid, spreadable fats like margarine and shortening.12

The process works by adding hydrogen atoms to the double bonds of unsaturated fatty acids in the presence of a catalyst, such as nickel. This chemical change has two primary effects that increase the melting point of the oil:31

• Saturation: By filling the points of unsaturation with hydrogen, the fatty acid chains become more saturated, which naturally increases their stability and melting point.12
• Isomerization: The process also triggers the rearrangement of molecular structures, converting natural cis fatty acids into trans isomers. Because these trans isomers have higher melting points than their natural counterparts, they contribute significantly to the hardening of the oil.24

By controlling these reactions, manufacturers can produce fats with specific textures and improved resistance to rancidity caused by oxidation.32