The modern method of oil extraction involves supplying a lot of heat. The oilseed is first crushed, and the pulp is heated under pressure. As a result, almost all the oil is extracted.

The downside is that the oil is heated up to temperatures of 230 degree centigrade. Heating it to such high temperatures alters the properties of the oil molecules in unfavourable ways (Polycyclic Aromatic Hydrocarbons  are formed at high temperatures which are carcinogenic) – and strips it off of its nutritional value.

For optimum extraction of oil, a solvent is added, in this case, hexane. The hazards of exposure to hexane are many – including dermatitis and CNS depression – depending upon the quantity of hexane inhaled or ingested.

The other option of extraction is using a method called “Expeller pressing“, which is a mechanical process of extraction using a machine called an expeller. No heat is added to the process, but heat can be produced as a result of the mechanical action on the nut – which could very well result in high temperatures that alter the chemical composition of the oil.
[16/08 4:20 pm] ‪+91 98206 07747‬: After subjecting the oil to such high temperatures, manufacturers tend to use preservatives to prevent the oil from becoming unstable. There is inconclusive evidence about whether these preservatives are harmful, but toxicology studies advise that it’s better to stay away from them.

Oils that have been refined through this process stay longer on the shelves and are more stable. This, however, is at the cost of its nutritional value.
[16/08 4:21 pm] ‪+91 98206 07747‬: Although pressing produces heat through friction, the oil seeds are not precooked and consequently the oil is considered cold pressed
[16/08 4:23 pm] ‪+91 98206 07747‬: I got info from Purandar Pr about company in pune which uses wooden churner and produces cold pressed oil
[16/08 4:23 pm] ‪+91 98206 07747‬: http://woodenchurner.com/other/