How Refined Oil Is Actually Made — Every Step of the Process

Most of the cooking oil sold in India is refined, and almost nobody who buys it could describe how it is made. That is not the buyer's fault. The process happens inside a factory nobody visits, it is described on the bottle in three words at most, and the two industries with an interest in explaining it — refiners and cold-press brands like us — both have obvious reasons to shade the story.

So here is the process, step by step, described as neutrally as we can manage. We press unrefined oil for a living and we are not going to pretend to be disinterested. But the steps below are engineering, not opinion, and you can check every one of them.

Step 1: Seed preparation

The seed is cleaned, dried, dehulled where relevant, cracked and flaked. Flaking matters: rolling the seed into thin flakes ruptures the cell walls, which is what lets oil come out easily later. Some seeds are also cooked at this stage, typically 80–100°C, which lowers viscosity and improves flow.

This is where the first divergence from a wooden ghaani happens. A ghaani takes whole or coarsely broken seed and crushes it cold. An industrial line pre-treats the seed specifically so that more oil will come out faster.

Step 2: Expeller pressing

The prepared flakes go through a screw press — an expeller — which squeezes out the bulk of the oil, typically leaving 6 to 12 percent still in the cake.

The press generates heat through friction and compression, commonly reaching 90–120°C at the outlet. This is worth pausing on, because "expeller pressed" is often marketed as a wholesome alternative to refined. It is a genuine step up from solvent extraction, but it is not a cold process, and the temperature reached is well above anything a slow wooden ghaani sees.

Step 3: Solvent extraction

The press cake still holds oil, and recovering it is where the economics of the whole category are decided.

The cake is washed with n-hexane, a petroleum-derived solvent that dissolves oil readily. The mixture is then heated so the hexane evaporates and is condensed for reuse, leaving the recovered oil behind. Recovery from the cake is close to complete — residual oil in the meal typically falls below 1 percent.

This step is the single biggest reason refined oil is cheap. It converts nearly all of the seed's oil into saleable product rather than into cattle feed. It is also the step that makes everything after it necessary, because solvent-extracted crude oil is not edible as it stands.

Residual hexane in the finished oil is regulated and is removed by the desolventising and deodorising steps that follow. In properly run plants the residue is at or below the level a lab can detect. We mention that because it is true and because a lot of writing on this subject implies otherwise.

Step 4: Degumming

Crude oil carries phospholipids — lecithin among them — which cloud the oil and cause it to foam and darken when heated. Water, or water with a little phosphoric or citric acid, is mixed in; the phospholipids hydrate, become insoluble, and are separated out by centrifuge.

The gums are not waste. Soy lecithin, a common food emulsifier, is this step's by-product.

Step 5: Neutralisation

Crude oil contains free fatty acids, which taste sour and smoke at low temperatures. Caustic soda — sodium hydroxide — is added, which converts them into soap. The soapstock is separated by centrifuge and the oil is washed.

The soapstock also goes on to a use: it is a raw material for the soap industry. Very little is thrown away in an oil refinery, which is part of why the finished oil can be sold so cheaply.

Step 6: Bleaching

The oil is mixed with activated bleaching earth — a treated clay — usually at 90–110°C under vacuum, then filtered. The clay adsorbs pigments: chlorophyll, carotenoids and the compounds that make crude oil dark.

Nothing is added to the oil here and nothing bleaches it in the household sense. Colour is taken out by adsorption. What also comes out, unavoidably, is a portion of the oil's natural tocopherols — vitamin E — and some of its phytosterols, because they adsorb onto the clay alongside the pigments.

Step 7: Winterising

Not every oil gets this step. Oils that carry waxes — sunflower, rice bran, cottonseed — are chilled, held, and filtered so the waxes crystallise out. Without it the oil goes cloudy in a cold kitchen, which consumers read as spoilage.

It is worth knowing this exists, because it is why a refined oil stays clear in the fridge and an unrefined one does not. Cloudiness in an unrefined oil is normal; it just means nobody removed the waxes.

Step 8: Deodorising

This is the defining step, and the one to understand if you only understand one.

The oil is heated under high vacuum to roughly 200–250°C and live steam is passed through it. Volatile compounds — everything that smells and tastes of the seed — are stripped out and condensed away.

The purpose is deliberate and commercial: industrial food buyers want an oil that contributes no flavour, so a biscuit tastes the same in every batch and a snack tastes the same in every state. Neutrality is the product specification, not an accident.

What leaves with the aroma is not only aroma. Most of the remaining tocopherols and sterols go too — they are volatile at those temperatures. Refiners often capture the deodoriser distillate and sell it; it is a commercial source of natural vitamin E. Some of that vitamin E is then sold back to the food industry as an additive.

Step 9: Antioxidants and packing

Having removed the compounds that protected the oil from oxidation, refiners add stabilisers back. TBHQ is the common one in India, permitted by the FSSAI up to 200 mg/kg in edible oils; BHA and BHT also appear. Synthetic or natural vitamin E may be added, and many brands fortify with vitamins A and D.

The result keeps for nine to twelve months, tolerates high heat, tastes of nothing, and costs a fraction of what an unrefined oil costs. Every one of those properties is a direct consequence of the steps above.

So what has actually happened to it?

Nine industrial steps, several of them involving heat above 100°C and one of them involving a petroleum solvent, with the explicit goal of producing a stable, neutral, long-lasting commodity fat.

It is worth being clear about what this is not. It is not adulteration, it is not illegal, and it is not a scandal. Refined oil is a legitimate, regulated food product that feeds most of India at a price most of India can afford, and the engineering behind it is genuinely impressive. Anyone selling you cold pressed oil by calling refined oil poison is overreaching, and we would rather not be that brand.

What is fair to say is narrower and, we think, more useful. The finished oil has been separated from the flavour, aroma and minor compounds it started with, on purpose, because those things are inconvenient at industrial scale. If that trade suits your kitchen, refined oil is a rational buy. If what you wanted from an oil was the part that gets removed, it is not.

The other half of this question — whether refined oil is bad for you, which is a different question from how it is made — we have answered separately and just as plainly.

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The short version: refined oil is made by pre-treating and heat-pressing the seed, washing the remaining cake in hexane, then degumming with acid, neutralising with caustic soda, bleaching with activated clay, chilling out the waxes, and steam-stripping the aroma at 200–250°C under vacuum before adding an antioxidant back in. Nine steps, all legal, all regulated, all aimed at producing a neutral, stable, cheap oil. The flavour and the seed's own vitamin E are removed deliberately, because at industrial scale they are liabilities.

We make the other kind. Our cold pressed oils are crushed slow in a wooden ghaani and bottled unrefined — one ingredient, no solvent, no bleaching earth, no deodorising column, and a four-to-six-month shelf life as a direct result. Batch-numbered and lab-tested. FSSAI licence 10724999001232. If you want the label vocabulary decoded, start with what "cold pressed" actually means.