Oils and fats from virtually all kinds of raw materials and ingredients can be modified into hard fats by altering their molecular structure.
This is done by hydrogenation – the name given to the process in which hydrogen is chemically combined with unsaturated oils and fats, by making it link up with the double bonds of the unsaturated fatty acid chains.
Essentially, this process consists of bubbling hydrogen gas through the oils, normally at temperatures of 150–200°C (302–392°F), under pressure, and in the presence of a catalyst. This adds the hydrogen atoms to the double bonds of unsaturated fatty acids, to either reduce them or to produce fully saturated fats.
Hydrogenation raises the melting point of oils and fats, and improves a range of other properties, including taste and keeping qualities.