1. Cold Pressing (Mechanical)
Cold pressed oils have the highest nutritional value, and if you are eating them also the best flavour and aroma.
Cold pressing involves grinding the vegetable, fruit, seed or nut using heavy granite millstone or stainless steel presses in such a way that the friction doesn't produce a lot of heat. By keeping temperatures below 49°C (120°F) the goodness of the oil is preserved. The lower you keep the temperature the better the oil you get.
Some oils such as grapeseed oil are never produced by cold pressing because you simply don't get much oil out of them with the method.
2. Expeller Method (Mechanical)
Under the expeller method oils are extracted using high pressure. Heat may also be used. If it is, temperatures as high as 85°C (185°F) are applied.
3. Solvent Extraction (Chemical)
Solvents can be used to extract carrier oils in the same way as they are used to extract essential oils.
With the solvent extraction method plant material is soaked in a solvent e.g. petroleum ether, methanol, ethanol or hexane. The cell membranes of the plant material are ruptured and the oil absorbed into the chemical.
The solvent is then separated and the oil bottled. However, some chemical residues are left from the solvent so the resulting oil is not 100% pure.
Personally, if I could prove that the solvent used was hexane and the price was much lower than with other oils then I would be happy to take my chances on this one because I spend a small fortune on ingredients for my DIY Hair Care Recipes.
You might also like:
- Neno Natural's Free DIY Shampoo Recipes
- How Are Essential Oils Extracted From Plants? (Steam Distillation, CO2 Extraction, Cold Press, Etc.)
whfoods.org, cold-pressed oils (about.com), Expeller Pressing (wikipedia),