How are Edible Oils Produced?

November 14, 2019

Have you ever wondered how cooking oils are produced? Why are some oils better than other for frying and some are only used for dressings? After spending years in the cooking oil industry I thought it was only right to share some of this information.

All vegetable oils are extracted from seeds, beans nuts or fruits by means of mechanical or Solvent extraction. The oil itself is chemically know as a triglyceride.

(3 x Fatty acids held together by glycerol)

Above: Triglyceride Molecule

Mechanical Extraction (AKA Cold Pressed)

Mechanical extraction is the most natural way of obtaining oil from seeds. Oils are removed from the seeds by either crushing, expelling or pressing. This is a traditional method and has produced oils such as extra virgin olive oils for many years. The reason I have mentioned extra virgin olive oil rather than just olive oil is because even though the oil may not conform to extra virgin specifications, olive oil can now be produced by solvent extraction (this will definitely not be extra virgin).

More recently cold pressing has been used to produce:

Rapeseed oil
Pumpkin seed oil
Hemp Oil
Avocado Oil

The oils are produced by crushing, settling and filtering. This method allows all organic material, which is soluble in oil the be present in the final product giving the oil colour and flavour. These “impurities” give cold pressed oils their own character and can vary from region to region and from different years.

Generally cold pressed oils are used for dressings, mayonnaise or as a finishing oil, rather than for cooking. Most cold pressed oils will lose some flavour the more you heat them up and may become bitter. It is believed that under high temperature cooking the impurities present in the oils may denature, and become carcinogenic

This doesn’t mean you shouldn’t cook with a cold pressed oil; it just means coating a steak with it or using it in a frying pan at smoke point won’t do you any favours. Cooking some

prawns over low to medium heat with extra virgin olive oil, chilli and garlic is a perfect example of how you can cook with a cold pressed oil.

Solvent Extraction

Above: ADM Plant Erith

The bulk of cooking oils sold today are manufactured by means of solvent extraction. It is the most cost-effective method for high volume and efficiency. This method produces a pure, flavourless oil suitable for high temperature cooking (deep frying at 190˚C, coating food, before grilling & pan frying near smoke point).

The process is as follows:

Rolling Cooking & Pressing

The grain is first heated to an optimal temperature of 35˚C before rolling the grain, rupturing the cell structure of the grain and creating a flake. The flake is then heated to around 90˚C to thermally rupture the cells, before using an expeller to extract the majority of oil whilst also forming a press cake.

Solvent Extraction

The remaining oil in the press cake is then removed using a series of solvent extractors. The oily press cake is washed with n-hexane, which dissolves the remaining oil and other soluble organic material into an oily solvent solution. The solvent is then recovered from the solution and press cake using heat and vacuum, leaving behind a crude oily mixture ready for refining.

Deodorisation & final refining

The crude oil is treated with water and acid, to strip out water soluble impurities such as phospholipids, gums, FFA’s colour pigments and residual hexane, before being steam treated to remove any unpleasant odours. The resulting oil is chemically pure and stable with a long shelf life. Most restaurants and fast food chains rely on this type of oil for cooking. Oils produced using this method are also used as an ingredient in commercially produced mayonnaise, pre made sauces & foods, soaps & cosmetics, chemical synthesis, biofuels and more.