The three most popular methods of oil extraction from vegetables, nuts and seeds are :


Chemical solvents

Centrifuge

Screw press (expeller)


Often, more than one method is used, this in order to squeeze the most oil out. The process usually begins with cracking the hull of the nut and then applying one of the aforementioned methods, followed by another.

The solvent extraction method is very popular, and uses hexane, which is a poisonous chemical. The process is very effective and usually recovers 99% of the oil. However, in order to get rid of the hexane, the oil is heated to a high temperature. This changes the flavor profile and for some delicate oils like olive oil, may ruin the flavor altogether.

Mechanical extraction is how things were done for centuries. Applying heavy pressure to olives or seeds until oil starts seeping out. An expeller is a big screw that is tightened until it crushes the nut/seed and causes the oil to run. This method provides yields of only 65-70% of the oil. Many companies then try to extract the rest of the oil using the chemical solvent.

Mechanical pressing may create high temperatures, especially when squeezing hard nuts. This usually happens when working with automatic machinery in high volume. The issue with high temperatures, as we mentioned before, is that they change the flavor of the oil.

Which brings us to the term "cold pressed". Some companies go to great efforts to maintain a temperature below 90 degrees Fahrenheit when pressing the oil. In Europe the term "cold pressed" is regulated and oils cannot exceed that temperature. But in the US, there is no such regulation. Cold pressed could mean anything under 400 degrees...