Vegetable oil is not always made with vegetables. Seeds like sunflower, rapeseed, soybeans, corn, cottonseed, flax, peanuts and olives are often used instead. Vegetable oils are typically used in cooking and as shortening in food production. They are also widely used in the production of margarine, and as an additive to plastics, cleaners, fuels and even nylon. The extraction of vegetable oil is now largely a mechanical process containing a few simple steps which can be duplicated at home with common kitchen devices.
Purchase the seeds from which you will be making your oil. Remove all foreign particles, shells, husks or skins of any kind, leaving just the edible material. If you are using corn, remove the corn from the husk and the skin from the kernel. If you are using olives, remove the pits and stems. Wash your seeds or vegetables before beginning the extraction process.
Grind your seeds using a coffee grinder or a food processor set on "Fine" for one minute. Inspect the results after the first pass. If large chunks or whole pieces remain, repeat the process. Lay your ground seeds flat onto a cookie sheet and heat them in the oven at 350 degrees for about 5 to 10 minutes or until lightly toasted. This will cause oils in the seeds to rise to the surface to be extracted. If you are using olives, skip the toasting step and instead mix the paste with a large spoon over a very low flame for a period of 20 to 30 minutes to draw out as much oil as possible prior to pressing.
Press the (toasted) seeds to extract the oil using a standard hand-held kitchen press. Collect the oil in a lidded plastic or glass container for later use.
Soybeans do not produce sufficient amounts of oil through pressing to make the process worthwhile. A solvent-only process may be used instead.
It may be hazardous to ingest vegetable oil which has not been purified after extraction. A host of chemical substances may be present in the oil until they are removed by process of distillation.
Do not attempt to extract vegetable oil from seeds using hexane at home. Hexane is potentially hazardous if not used correctly. The press method may produce less oil, but it is far safer.