How can corn oil be turned into margarine?

Corn oil is converted into margarine primarily through a process called hydrogenation.1

Because corn oil is naturally liquid at room temperature, it must be hardened to achieve the consistency required for margarine. During hydrogenation, the oil is combined with hydrogen at high temperatures and pressures in the presence of a catalyst, such as nickel. This process adds hydrogen to the unsaturated double bonds of the oil's fatty acid chains, converting them into higher-melting saturated products.2314

In addition to hardening the oil, this reaction can cause isomerization, where the molecular structure rearranges to form isomers with higher melting points, further contributing to the solid texture. Once the oil has been hardened, it is blended with other ingredients—such as water, milk products, salt, emulsifiers, and vitamins—to create the final margarine product. While many margarines historically relied on hydrogenated oils, many modern versions are now produced using non-hydrogenated oils to reduce the presence of trans fats.563