Cold pressed oils are gaining popularity in comparison to refined/solvent based-oils available in the market. They are fast replacing industrially-produced oils, but what does a cold pressed oil really mean and is there any real difference between them?
Cold-pressed vs Heat-solvent oils
Cold pressed oils are not really new to the market. They have been existing for centuries, but were pushed to the rural markets with the advent of new technologies and modern living. Different cooking requirements also shaped the changing scenario of the oil extracting techniques. In recent years, with more research available and health taking a priority, cold pressed oils are making a come-back to the kitchen.
The term ‘cold pressed’ may mislead one to believe that oil extraction is done in cold temperatures. However, that is not the case. Cold pressed simply means mechanical pressing of seeds to remove oils without the use of heat-solvents. In reality, all crushing of seeds will generate friction that will produce some amount of heat. Cold pressing is really about minimising heat and keeping the seeds as cool as possible while extracting oils.
Oils that are extracted using heat-solvents are called 'heat-solvent based oils' or even refined oils.
Here is a quick guide on how to spot the difference between cold-pressed and heat-solvent oils.
- Extraction process
- Production or yield
- Oil recovery process
- Free fatty acids
- Trans fatty acids
- Nutrition
- Preservatives & additives
- Environmental cost
1.Extraction process
Oils are extracted from nuts, grains, husk and other fibrous material by pressing them. And there are more than one way to extract this oil.
Cold pressing is really about minimising heat and keeping the seeds as cool as possible while extracting oils. Typically it requires mechanical power and does not need organic solvents and the temperature can be kept under 50 °C or lower (depending upon the machine used) to perform cold pressing. This dramatically affects the preservation of nutritional compounds of the oil.
Most industrially produced oils usually use ‘solvent-extraction (heat-solvents)’ method to extract oils from plant-seeds and others. A solvent is a molecule that has the unique ability to dissolve with other molecules and pull them from their fibrous or solid material (in the case of seed oils - the seed meal or fibrous content of a seed). The industry mostly uses hexane-gas, a chemical solvent derived from petroleum that has the capability to dissolve and mix with the oils during the extraction process, which literally washes out the oil from the seed shell.
The other aspect of solvent-extraction is the application of heat. Hexane is more efficient at extracting oils than petroleum at higher temperatures. Hence, seeds are heated to higher temperatures to extract oils. Application of heat changes the molecular bonds of the oils and produces undesirable free fatty acids, peroxides, and p-anisidine among other changes.
2.Production or yield
The yields produced vastly differ for both the aforementioned processes. The total quantity produced, therefore cost of production, becomes the yardstick for choice of operation. ‘Heat-solvent’ extraction method is preferred by the industry, as it is far more efficient in extracting oil from a seed vs cold pressed method. Remarkably, it is capable of removing virtually all of the oil available in the oil seed giving a yield of 60-70% or more. On the other hand, cold pressed method yields only 30-40% oil, rendering it to be more expensive as a method of extraction.
3.Oil recovery process
Heat-solvent oils need to undergo ‘oil-recovery’ or ‘re-fining’ process once the oil is extracted. This recovery process separates the dissolved hexane from oil by evaporation and distillation and other methods. Usually, heat-solvent oils undergo the following steps to separate the residual hexane from the edible oil:
- Degumming (to remove gums)
- Neutralizing (to remove free fatty acids)
- Bleaching (to remove color),
- Deodorizing (to remove odor and taste)
- Dewaxing or Winterization (to remove waxes)
Harsh treatments, chemicals, very high heat, and straining are used to remove the solvent from the oil. These processes render the oil inferior in taste, fragrance, appearance and especially nutritional quality.
Cold pressed oils, on the other hand, are obtained without undergoing any such treatment or without altering the oil. The oil is mechanically pressed and separated and is left as is. It is allowed to sediment over a period of time and once the sediment has settled, the oil is filtered using cheesecloth to get pure, raw and unrefined oil. No nutritional loss occurs.
4.Free Fatty Acids
Quality of commercial oils and fats is determined by the presence or rather the absence of Free Fatty Acids (FFA). One of the main by-products of the heat-solvent method is the production of free fatty acids (FFA) due to hydrolysis of oils and due to application of heat. Higher temperatures produce higher amounts of free fatty acids. FFA are less stable than neutral oil (or unrefined oil) and easily oxidize and become rancid. They are also associated with the undesirable darkening of colour, off-flavouring and may also reduce the smoke point of an oil. Furthermore, deterioration of the quality may lead to reactive and toxic product formation that can be hazardous to health.
Hence, FFAs are reduced or neutralised from refined oils (or heat-solvent oils) through application of soapstock or bleaching and deodorizing among other refining processes.
On the other hand, natural and cold pressed oils are primarily composed of naturally occurring glycerides of fatty acid obtained only from vegetable sources. No production of free fatty acids happens due to extraction methods.
5.Trans Fatty Acids
Heat-solvent oils may be hydrogenated. Hydrogenation is the process whereby a hydrogen molecule is added to the oil in the presence of a catalyst. Hydrogenation of oil, is a useful process as it allows modification of characteristics to maximise use of the oil such as different melting points will have different industry application or production of more stable oil. However, hydrogenation produces undesirable trans fatty acids, which have been directly linked to coronary heart diseases and other health risks.
World health organisation has called for the global elimination of industry produced trans fatty acids in fats and oils. Many countries have banned partially hydrogenated fats and oils, however, India has issued a limit of 5% trans fatty acid in fats/oils instead.
Cold pressed oils, as per a study, did not show any presence of trans fatty acids isomers, whereas in refined oils, subjected to refining and deodorising processes, these isomers occurred at approx 1%.
6.Nutritional Properties
Cold pressed oils are mostly single pressed oils. A study was conducted on lemon seed oils that compared the quality and stability of oils using both methods - cold pressed vs hexane-extraction. Evidence showed that free fatty acids, ACs, peroxide values and p-anisidine values were significantly lower in cold pressed oils, indicating a superior quality of oil. These oils typically also had higher phenolic content and antioxidant capacity, suggesting higher oil stability and nutritional value.
Research also indicates higher levels of bio-active compounds in cold pressed oils. Furthermore, they contain valuable nutrients such as — essential fatty acids, phospholipids, antioxidants such as tocopherols (eg. Vitamin-E) & phosphatides (eg Lecithin), sterols, hydrocarbons (squalene), carotenoids among others. Much more than their heat-solvent / refined oil counterparts.
7.Preservatives and additives
No chemicals, additives, or preservatives are added to virgin or cold-pressed oils. These oils contain natural flavours and aromas. Conversely, heat-solvent oils are deodorized, bleached, coloured, and processed extensively to obtain specific flavour, colour, taste and aroma.
8.Environmental cost
One must also evaluate the hidden environmental cost of both extraction methods. Cold pressed or wooden kohlu processes are simple, mechanical and chemical-free. Little energy is required to operate these machines. And most importantly, they are safe to operate and free from any production of toxic fumes or by-products.
On the contrary, several studies have revealed that hexane is highly toxic and can affect the neural system when inhaled by humans. Residual hexane causes toxicity and hence can be extremely hazardous. Moreover, hexane can easily escape into the environment, during the production process, and react with pollutants to form ozone and photo chemicals.
Conclusion: Cold pressed oils are gaining popularity among individuals who are looking to move to healthier alternatives and are looking for additive-free, preservative-free ingredients as a cooking medium.
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Reference list
1. https://link.springer.com/article/10.1007%2Fs11947-012-0947-x
2. https://www.uvm.edu/sites/default/files/media/Oilseed_Presses.pdf
4. https://asset-pdf.scinapse.io/prod/2186140083/2186140083.pdf
5. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5495713/
6. https://pubs.rsc.org/en/content/articlelanding/2014/ay/c4ay00344f
7. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/free-fatty-acids
8. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6045989/
9. https://bmcresnotes.biomedcentral.com/articles/10.1186/s13104-019-4831-x
10. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/free-fatty-acids
11. https://www.karger.com/Article/Pdf/229006
13. https://www.academia.edu/42769593/Functional_and_Nutritional_Health_Benefit_of_Cold_Pressed_Oils
14. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5495713/
15. https://www.academia.edu/42769593/Functional_and_Nutritional_Health_Benefit_of_Cold_Pressed_Oils