Refined oil is made using several processing agents: hexane to extract oil from the seed, alkali to remove free fatty acids, acid-activated clay to bleach, and sometimes added antioxidants. Most are removed before bottling and regulators set limits. The real questions are what remains, what high-heat refining creates, and whether you want that in a daily staple.
Last updated: 6 Oct 2026 | Shop cold pressed groundnut oil
“Chemicals in refined oil” is a phrase that gets used to alarm people, and it is also a legitimate question. Refining is an industrial process and it does use chemical agents. This page lays out which ones, why they are used, what is removed again, what can remain, and what the evidence does and does not show, so you can make an informed choice without scare claims.
We press unrefined oil at our own mill in Nagpur, so we have a preference. We have kept this page to what is documented, and we say where the evidence is weaker than the headlines.
Which chemicals are used to make refined oil?
The table follows a typical refining line. Details differ between plants and between oils, but the stages are standard.
| Stage | Agent used | Purpose | What happens to it |
|---|---|---|---|
| Solvent extraction | Hexane (a petroleum-derived solvent) | Dissolve the last of the oil out of the crushed seed | Evaporated and recovered; maximum residue limits apply |
| Degumming | Water, or phosphoric or citric acid | Remove gums (phospholipids) that cloud the oil | Separated out with the gums |
| Neutralising | Caustic soda (sodium hydroxide) | Remove free fatty acids | Removed as soapstock; the oil is washed |
| Bleaching | Acid-activated clay (bleaching earth), sometimes carbon | Remove pigments such as chlorophyll and carotenoids | Filtered out of the oil |
| Deodorising | Steam at high temperature under vacuum | Strip volatile compounds that give smell and flavour | Distillate is removed; heat can create by-products |
| Optional additives | Permitted antioxidants (INS 319, 320, 321); sometimes an anti-foaming agent in frying oils | Extend shelf life or reduce foaming | Remain in the oil within permitted limits and should appear on the label |
What stays in the oil?
Most of the agents above are removed by design. Caustic soda leaves with the soapstock, bleaching clay is filtered out, and steam carries volatile compounds away. Hexane is evaporated and recovered, and food regulators set maximum residue limits for what can remain. Measured residues in properly refined oil are typically low.
The agents that can remain in the finished oil are the ones added on purpose, such as antioxidants and anti-foaming agents, and trace solvent residue within the legal limit. Permitted additives appear on the label, often as INS numbers. A well-run refinery stays within the limits, but that is a compliance question, and staying within a limit is not proof that an ingredient is harmless or that it is something you want in the oil you eat every day.
By-products that refining can create
Some of the more interesting concerns are not about agents that are added, but about compounds formed by the process itself:
- Trans fats. Prolonged high-temperature deodorising can form small amounts of trans fatty acids. Partial hydrogenation, used for some shortenings and vanaspati, creates much more. Industrial trans fat is linked to heart disease, which is why FSSAI caps it in oils and fats at 2 per cent of total fat.
- 3-MCPD esters and glycidyl esters. These process contaminants form when oils are heated to high temperatures during deodorising. They have been found at the highest levels in refined palm oil. The European Food Safety Authority assessed them in 2016 and flagged a potential health concern for younger age groups with high intake. The EU has since set maximum levels, and producers have changed processes to reduce them.
- Lost minor compounds. Bleaching and deodorising reduce vitamin E, plant sterols, polyphenols and aroma compounds that the seed carried. This is a loss of something good rather than the addition of something harmful, and we cover it in what is refined oil.
What the evidence does and does not show
You may have read that refined oil causes cancer, hormonal disorders or nerve damage. The evidence does not support a claim that simple. Hexane is a neurotoxic solvent at high occupational exposure, when workers breathe it in quantity, but that is very different from trace residues regulated in food. Soybeans contain plant compounds that can mimic hormones in laboratory settings, but refined soybean oil carries only traces of them, and nothing here establishes that cooking oil causes conditions such as PCOS or endometriosis.
Where the evidence is stronger is narrower and applies to any oil, refined or not. Industrial trans fats raise the risk of heart disease. Oil that is heated repeatedly or taken past its smoke point breaks down into compounds you do not want to eat. A diet heavy in fried and packaged food is linked to poorer health outcomes whichever oil is used. Those are good reasons to limit reheated oil and fried food, whatever is in the bottle.
Why some people still choose to avoid refined oil
The reasonable case for unrefined oil is a preference for less processing, not a claim that refined oil is toxic. People who avoid refined oil usually say they want to avoid a solvent-based process, have fewer additives to read about, keep more of the seed's natural compounds, and enjoy the flavour of an oil that tastes of its seed. Those are legitimate reasons, and the choice is yours. For a broader view of the trade-offs, see cold pressed oil vs refined oil and our overview of the hazards people associate with refined oil.
How to read an oil label
- “Refined”, “double refined” or “edible vegetable oil” means the oil has been through a refining line.
- INS 319, 320 or 321 in the ingredients means an antioxidant (TBHQ, BHA or BHT) has been added within permitted limits.
- “Blended” oils combine two or more oils, and the label should list them.
- “Filtered” is not “unrefined”. A filtered oil can be refined or unrefined, so look for the word “refined” or ask the producer.
- Hexane is not listed because it is a processing aid. If you want to avoid solvent extraction, choose an oil whose producer says plainly that it is only pressed and filtered.
What we use instead: pressing without any of these agents
At our mill in Hudkeshwar, Nagpur, seeds are crushed in a wooden ghani that turns slowly, so friction heat stays low. The oil is filtered, rested and bottled at the same site. There is no hexane, no caustic soda, no bleaching clay, no deodorising and no additives. You can see each step on our Nagpur oil mill page.
If you want to try it, cold pressed groundnut oil is the easiest oil to start with for everyday Indian cooking, and sesame oil suits tempering and chutneys. Because the label “cold pressed” is not tightly regulated, our guide to testing cold pressed oil at home is worth reading before you buy from any brand.
Frequently asked questions
What chemicals are used in refined oil?
Refining typically uses hexane to extract oil from seed, water or food-grade acid for degumming, caustic soda to neutralise free fatty acids, acid-activated clay to bleach, and steam for deodorising. Some oils also contain permitted antioxidants such as TBHQ, BHA or BHT. Most processing agents are removed before bottling.
Is there hexane in refined oil?
Hexane is used to extract oil from seed and is then evaporated and recovered. Regulators set maximum residue limits for what may remain in the finished oil, and measured residues in properly refined oil are typically low. Cold pressed oil involves no solvent at all, so there is no hexane to begin with.
Does refined oil cause cancer?
The evidence does not support a blanket claim that refined oil causes cancer. Concerns relate to specific by-products, such as industrial trans fats and heat-formed contaminants like glycidyl esters, which regulators monitor and limit. Repeatedly reheated oil is also a concern. These issues apply to any oil heated or processed badly, not just refined oil.
What are INS 319, 320 and 321 on an oil label?
They are the codes for synthetic antioxidants added to extend shelf life: INS 319 is TBHQ, INS 320 is BHA and INS 321 is BHT. Indian regulations permit them in certain foods within set limits, and they must be declared on the label. Unrefined oils such as wood-pressed oil usually contain none.
Is refined oil unsafe to cook with?
Refined oil sold in India must meet FSSAI standards and is widely used, so it is not unsafe by definition. The sensible precautions apply to every oil: do not heat it past its smoke point, do not reuse frying oil repeatedly, and buy from a producer that follows regulations and labels clearly.
How can I avoid chemically processed oil?
Choose an oil whose producer states that it is pressed mechanically and only filtered, and ask where and on what equipment it is pressed. Check the label for the word refined and for INS numbers. Producers that own their mill can answer these questions directly, while those that only bottle cannot.
Written by Dushyant Waghmare, founder — Parampara Naturals, who operates a wooden ghani oil mill in Nagpur.
Last updated: 6 Oct 2026