Why the Oil Extraction Method Affects What You Are Actually Eating

We put a lot of thought into what goes into our food, the quality of vegetables, the freshness of spices, whether the dal is organic or not. We rarely put the same thought into the oil we cook everything in. And yet, in most Indian meals, everything passes through oil at some point. The tadka, the curry base, the stir-fry, the marinade.

Oil is the medium through which heat reaches food, the carrier that absorbs fat-soluble spice compounds and distributes them through a dish, and the source of fatty acids that your body uses for energy and cellular function. What happens to that oil before it reaches your kitchen shapes all of those functions.

Oil Is Not Just Fat

The fatty acids in an oil, the saturated, monounsaturated, and polyunsaturated components listed on every nutrition label, are its structural backbone. But a seed-derived oil in its natural state contains much more than fatty acids.

Within the lipid fraction of any natural seed oil, you will find tocopherols (the Vitamin E family, present as alpha-, beta-, gamma-, and delta-tocopherol in varying ratios depending on the seed), tocotrienols, phytosterols (plant-based sterols structurally similar to cholesterol), phospholipids (including lecithin), carotenoids, and polyphenols. You will also find volatile aroma compounds, the hundreds of molecules that make cold-pressed groundnut oil smell like roasted peanuts and cold-pressed mustard oil smell like mustard.

These compounds are not incidental. They are part of what the seed contains, shaped by evolution over millions of years to perform specific biological functions. They are also the first casualties of industrial oil processing.

What Specifically Happens to Tocopherols

Tocopherols are the primary natural antioxidants in vegetable oils. They protect the oil’s polyunsaturated fatty acids from oxidation during storage and during moderate cooking. Alpha-tocopherol is the form most biologically active in human nutrition. Gamma-tocopherol is particularly effective as a lipid-phase antioxidant.

During refining, tocopherols are lost at multiple stages. High-temperature pre-pressing reduces them. The deodorisation step, which involves steam stripping at 200–270°C, causes significant loss. Studies on refined versus cold pressed versions of the same oils consistently show that cold pressed oils retain substantially more tocopherols. For groundnut oil specifically, published analyses show cold pressed samples containing 400–600 mg/kg total tocopherols compared to refined samples in the 150–300 mg/kg range, depending on the specific refining conditions.

Because tocopherols are the oil’s natural preservative system, their loss in refined oil is partly why synthetic antioxidants like TBHQ are added back after refining, to replace the preservation function that was refined out.

What Happens to Polyphenols

Cold pressed oils, particularly extra-virgin olive oil and cold pressed mustard oil, contain polyphenolic compounds that are almost entirely absent in their refined counterparts. In olive oil, these polyphenols (oleocanthal, hydroxytyrosol, oleuropein) are the subject of significant nutritional research. In mustard oil, the isothiocyanates that form from glucosinolates during cold pressing are another class of bioactive compounds completely destroyed at refining temperatures.

We are not claiming these compounds produce specific health outcomes in the amounts present in cooking oil, that would require controlled human clinical trials specific to each compound and dose, which largely do not exist for Indian seed oils. What we are saying is that these compounds are part of the natural composition of the seed, they are present in cold pressed oil, and they are absent in refined oil.

Whether their absence matters to your health over a lifetime of cooking is a question nutritional science has not yet answered definitively for most Indian seed oils. What is definitively answered is that they are there in cold pressed oil and not in refined oil.

Phytosterols: What They Are and Why They Disappear

Phytosterols are plant-based compounds structurally similar to cholesterol. They occur naturally in seed oils and are removed during the degumming and bleaching steps of refining. Some refined oil manufacturers actually add phytosterol concentrates back into their products and market them as ‘heart-healthy’, the phytosterols being the selling point.

Cold pressed oil contains phytosterols naturally, as part of its unaltered composition. The total sterol content of cold pressed groundnut oil is approximately 1,500–2,500 mg/kg, with beta-sitosterol as the primary component. In refined groundnut oil, these values are substantially lower, the exact reduction depends on refining conditions.

The Fatty Acid Question: More Similar Than Different, But Not Identical

The major fatty acid profiles of cold pressed and refined versions of the same oil are broadly similar. Both cold pressed and refined groundnut oil are predominantly oleic acid (about 40–50%), with significant linoleic acid (30–35%) and some palmitic acid (10–12%). The same types of fats are present.

However, high-temperature processing during extraction and refining causes some oxidation and thermal degradation of polyunsaturated fatty acids. The extent depends on temperature and duration. Published comparisons of cold pressed versus refined groundnut and sesame oils show slightly higher oxidative markers (peroxide values, p-anisidine values) in refined oils before the addition of synthetic antioxidants, suggesting that processing does cause measurable lipid degradation.

The addition of TBHQ or other antioxidants in refined oil addresses oxidative stability for shelf life purposes. But it is a synthetic substitute for the natural antioxidant protection that processing removes.

What About Cooking Performance?

Cold pressed oils are sometimes characterised as ‘delicate’ and inappropriate for high-heat cooking. This framing is partially misleading. The smoke points of well-made cold pressed oils, while lower than their refined equivalents, are entirely adequate for the majority of Indian home cooking. Cold pressed groundnut oil has a smoke point in the 160–180°C range. Standard Indian tadka, sauteing, and curry-making routinely occurs below this threshold.

Where refined oil genuinely has an advantage is in very prolonged, very high-temperature deep frying, commercial-scale continuous frying operations, for instance. For home cooking, where a family fries for 10–15 minutes at 160–175°C and then turns off the heat, the smoke point advantage of refined oil is rarely relevant.

The practical conclusion: for everyday home cooking, cold pressed oil performs the job fully. For the edge cases of very high sustained frying temperatures, refined oil has a technical advantage, though that advantage is often overstated in marketing.

Related Reading

• Cold Pressed vs Refined Oil: What Actually Changes in the Process [→ Blog 2]
• Smoke Points of Common Cooking Oils: What They Mean for Your Kitchen [→ Blog 8]
• How to Read an Edible Oil Label in India: What the Terms Mean [→ Blog 7]

Deepak