The properties of highly unsaturated oils that make them valuable, also make them undesirable for food products because they tend to turn rancid readily. This raises the melting point. Originally done by Wesson. Some of the chemical features are diagrammed on page 320. Many important oils are listed on page 330-331.
Many seeds contain quite large quantities of oils.
Sesame seed, for example, is more than half oil. Extraction methods Crushing - today done mostly with rollers. A screw press makes it possible to have a continuous feeding of seeds. The seeds are usually cleaned and then dehusked. In some cases the kernels are broken or flaked before extraction.