Hydrogenation, the chemical reaction between molecular hydrogen and an element or compound, ordinarily in the presence of a catalyst.
It involves the reaction between unsaturated liquid oil and hydrogen adsorbed on a metal catalyst.
The oil is mixed with a suitable catalyst (usually nickel), heated (140–225°C), then exposed, while stirred, to hydrogen.
In the food industry, hydrogen is added to oils (through hydrogenation) to make them more solid, or 'spreadable'.
Hydrogenated oils can be sold directly as 'spreads', but are also used in the food industry in the manufacture of many foodstuffs such as biscuits and cakes.
The use of hydrogen helps to prolong the shelf-life of the food and maintain flavour stability.