The Secret Behind Supermarket Oil Bottles: Are Refined Plant Oils Really Good for You?
Let’s begin with a quick test: what happened on 2 July 2024? Without reaching for your phone, take a moment to recall. I guarantee that the vast majority will have forgotten. When I searched online on this date in 2025, I found not a single reference to the tanker truck incident from a year earlier. The correct answer: on that very day, *Beijing News* exposed the practice of using uncleaned tanker trucks to mix and transport edible oils alongside chemical liquids.
Once the scandal broke, authorities moved to rectify regulatory lapses, the implicated companies issued apologies for their oversight, and the unscrupulous ‘oil vessels’ were roundly condemned. Life soon returned to its tranquil, blissful rhythm, and everyone carried on happily ever after. Food enthusiasts, however, were left feeling bitterly chagrined and oddly bereft, which is precisely what prompted this article.
I.Oil Vessel or Chamber Pot?
Following the tanker scandal, a particularly sharp remark has been circulating: “The real issue isn’t whether the tanks are properly cleaned. It’s that mineral and edible oils should never share the same vessel in the first place. No matter how thoroughly you clean a chamber pot, would you really use it to brew your tea?”
Every household has an oil dispenser. The modern kitchen version is usually sleek and compact, prized for a drip-proof spout and matching the décor. The larger version is simply the bulk plastic bottle you carry home from the supermarket. These supermarket vegetable oils bear well-known brand names and come from massive producers churning out thousands or even tens of thousands of tonnes annually. Just as processing is essential, so too is storage and transport—they are indispensable links in the long, global supply chain that takes oil from crop to kitchen. In that sense, the tanker truck is merely a giant oil dispenser.
The public outcry over these shared tankers carrying edible oil has been fierce. As a food lover with a keen interest in food health and food sovereignty, I found myself utterly baffled by the whole affair. The scandal is undoubtedly foul and wholly deserves condemnation, but I hope people will take this moment to look a little deeper and question the very substance being called “oil”.
When it comes to the “oil” inside those containers, the news is bleak. One revelation is bad, and the other is just as disheartening.
The first is that the supermarket vegetable oils we buy are no longer “oil” in any traditional sense. The practice of “mixed loading”—sharing tanks between edible oils and inedible industrial chemicals—has been happening for years, continues today, and is likely to persist.
In a culinary context, the oils of the agricultural era were either rendered animal fats or pressed plant seed oils. Long before humans mastered rendering and pressing techniques, animal fats and oil-rich seeds had already ebbed and flowed through human diets for millennia. Dietary fats are an essential nutrient, fundamental to life, and were instrumental in humanity’s triumph in natural selection. Countless lineages that could not secure enough fat were culled by evolution. Frankly, I owe a quiet bow to dietary fats for preserving this humble life of mine.
I’ll leave animal fats aside for now, as virtually all commercially available “cooking oils” today are plant-based. Yet they bear little resemblance to the oils that nourished humanity throughout our evolutionary history.
Why the distinction? Let’s begin with the extraction process.
Once agriculture took hold and oilseed crops became widely available, both Eastern and Western societies turned to mechanical pressing to squeeze oil from seeds. But the game changed in 1843, when carbon disulphide was first used to extract olive oil. France quickly led the field in solvent extraction research, only to be overtaken by Germany, which established the first battery-type extraction plant for industrial-scale production. The German engineers also invented the continuous basket-type extractor, dramatically boosting efficiency. The baton then passed to the United States, which introduced the highly efficient horizontal rotary extractor in 1949; its mass adoption soon came to dominate global production. In 1955, China completed its first continuous solvent extraction plant in Jilin.
The 1950s marked an era of rapid expansion for both the food industry and globalisation, as sugar and refined vegetable oils steadily came to dominate our diets. The masterminds behind this shift were the food giants. Michael Moss’s book *Salt, Sugar, Fat: How the Food Giants Hooked Us* presents a wealth of documented cases, revealing how these corporations have stopped at nothing—from pouring fortunes into advertising to allegedly funding scientists to produce misleading research.
Before solvent-extracted seed oils reach supermarket shelves, they undergo two high-heat treatments in the factory. The extraction process is divided into three types—pre-press extraction, single extraction, and double extraction—though the underlying principles are broadly similar. n-Hexane dissolves the fats within the raw materials to create a mixed oil, which is then subjected to two heating stages. The first stage strips away the solvent, while the second applies high heat to decolourise, deodorise, and filter out impurities. The final product is a purified, odourless, clear refined vegetable oil, ready to take its place on supermarket shelves and in domestic kitchens.
Today, the solvent most commonly used in the extraction process is n-hexane—a petrochemical product that is unfit for consumption and harmful to health.
Traces of this solvent inevitably remain in the vegetable oil. According to the *National Food Safety Standard for Vegetable Oils*, the permissible solvent residue limit for edible vegetable oils produced via the extraction method (including blended oils) is ≤20 mg/kg. For mechanically pressed oils, solvent residues must not be detectable (readings below 10 mg/kg are classified as non-detectable). The European Union enforces a significantly stricter standard for solvent residues in cooking oils; the current safety limit stands at 1 mg/kg, making it ten to twenty times more stringent than the Chinese standard.
II. Industrial Alchemy: Turning Oil into Inflammation
Clutching a traditional cold-pressed oil label while browsing supermarket aisles is a rather futile exercise. It is akin to trying to locate the Great Sage Equal to Heaven using Sun Wukong’s original identification, only to discover he has long since attained enlightenment and become the Victorious Fighting Buddha. The unrefined oil consumers are looking for simply no longer exists on these shelves.
The second piece of unwelcome news: supermarket oils may not only contain solvent residues, but could also harbour trans fats.
Trans fats are not exclusive to hydrogenated vegetable oils; they are also generated during the refining process and through high-temperature cooking.
When vegetable oils are subjected to multiple rounds of high-heat processing, the first piece of bad news is that heat-sensitive nutrients naturally found in plant seeds—such as the antioxidants vitamin E and phytosterols—are completely wiped out. The second piece of bad news is that monounsaturated fatty acids and polyunsaturated fatty acids, which played such a pivotal role in human evolution over millennia, are also largely destroyed. And here is the worst news of all: matter is neither created nor destroyed. After churning through industrial furnaces and undergoing a radical transformation, a portion of it re-emerges as trans fats—the very compounds that modern consumers dread.
If you share my habit of diving into research with a mix of curiosity and half-formed theories, you will inevitably stumble across conflicting information. Some literature points to potential solvent residues in finished oils, while other sources warn of carcinogens such as benzo[a]pyrene forming during processing. Conversely, official health bodies insist that harmful substances in certified products remain within safe, controllable limits. I choose to believe; after all, God helps the faithful.
Moreover, vegetable oils have emerged as pro-inflammatory agents posing a widespread threat to modern health.
Vegetable oils contain essential fatty acids that the human body cannot synthesise on its own: linoleic acid (ω-6) and α-linolenic acid (ω-3). Although plant seed oils do contain ω-3, the quantities are minimal. The richest sources are wild fatty fish, free-range poultry and duck eggs, grass-fed beef and lamb, and full-fat dairy. Relying on plant seed oils to meet the body’s ω-3 requirements is fundamentally counterproductive.
Yet the more troubling news concerns ω-6 excess. The ideal ratio of ω-3 to ω-6 lies between 1:1 and 1:4. Plant seed oils are heavily skewed towards ω-6, which is already abundant throughout the food chain. Since humans are never short of it, the increasing consumption of plant seed oils has pushed the dietary ratio to 1:15 or even higher. This severe imbalance fuels inflammation, accelerates ageing, and drives oxidative stress, posing a serious risk to health.
Despite all these controversies, the reason solvent-extracted seed oils have conquered the global market is remarkably simple. I have grown rapeseed and peanuts myself and pressed oil by hand using a small domestic machine. Rapeseeds, with an oil content of roughly 40 per cent (37.5–46.3 per cent), yield barely one tael of oil per jin when manually pressed—a yield of just over 10 per cent. Sending them to a rural mill for hot pressing raises the yield to somewhere between 20 and 30 per cent. With these traditional pressing methods, nearly half the oil remains trapped in the spent seed cake. By contrast, the solvent extraction process can achieve an oil recovery rate of up to 99 per cent.
III. The Clumsy Bear Survives; the Clever Person Perishes
When it comes to plant seed oils, modern people have certainly outdone themselves. Oil extraction rates keep climbing, supermarket oil keeps getting cheaper, and ready-made and semi-finished foods packed with oil are easier to come by than ever. We keep driving further, relentlessly, right up to the grave.
I once read this line: “Nature does not produce harmful food, but factories do.” (Nature does not make unhealthy food, but factory does.)
As a fairly straightforward person, I stick to a straightforward approach: a blanket ban, no exceptions. I shun supermarket oils entirely, skip takeaways, and avoid any ready-made or semi-finished foods that contain oil. Here is exactly how I do it:
1. No stir-frying. Vegetables are excellent, but stir-frying them is not. Heating plant oils to high temperatures generates trans fats just the same. Vegetables can be enjoyed raw in salads, or roasted, steamed, or blanched. Electric ovens and air fryers are modern luxuries. Take eggplants, notorious oil-sponges when stir-fried: toss them in the oven or air fryer with pointed peppers and garlic for ten minutes, mash them up with salt and seasoning, and you have a wonderfully savoury side dish. I can’t handle spicy food, so I skip the chillies. I’ve heard that mashing in century eggs alongside the other ingredients yields “Lei cai”, a classic home-style dish from Hunan.
An electric griddle is another daily staple in my kitchen. As I don’t eat meat, I use it to fry eggs every day. Originally, I cooked them oil-free: just eggs and assorted vegetables with a bit of silken tofu, poured straight onto the preheated griddle. Later, I happened to stop buying commercial tofu, and worrying about it sticking to the pan, I switched to using just a drop of oil for the eggs. This keeps my oil consumption incredibly low. For those who eat meat, you could try stir-frying minced meat and eggs with water in place of oil—use twice as much water as you would oil. Once the water boils in the hot pan, add pre-marinated ingredients like diced prawns, minced meat, mushrooms, and wood ear mushrooms. When it boils again, pour in the beaten eggs and toss everything together. This method mirrors a regional speciality from Changwu in Shaanxi province. You might also find inspiration in Foodthink’s previous articles on stir-fried sauces; a single batch will keep you going for weeks.
Second, choose a reliable oil. Even without stir-frying, I still use oil occasionally. I prefer walnut oil from Kang Li, a Yi woman and fellow producer at the Beijing Organic Farmers’ Market. I typically buy six small bottles (totaling 1.5 kg) after the Lunar New Year, and to this day I still have three unopened. That works out to less than 3 grams per day on average. This year alone, I harvested around 25 kg of rapeseeds and over 50 kg of peanuts in their shells, so I shouldn’t need to buy oil going forward.
Thirdly, make your own treats to satisfy cravings. Foodthink has previously published an article on my homemade mooncakes. That version featured a water-oil dough made with walnut oil. While the homemade filling contained no additives, the recipe still required quite a bit of oil. I later developed oil-free versions of taro and salted egg yolk pastries, as well as red bean paste and salted egg yolk pastries, using oat flour as the main ingredient for the crust. You can also bake oil-free biscuits using crushed dates, oats, black sesame seeds, steamed buckwheat, and egg yolk. These snacks are tasty, healthy, and completely guilt-free. I’ll share the full recipes in a future post.
Replace refined vegetable oils with whole nuts and oilseeds. Dietary fats are essential nutrients for the body. Fat-soluble vitamins rely on them for proper absorption, so getting your daily intake is vital. The body cannot synthesise many of these nutrients on its own, particularly omega-3 fatty acids. My approach is to eat omega-3-rich nuts, such as walnuts, alongside minimally processed options like black sesame paste.
Fourth, for home-grown peanuts, the most common ways to enjoy them are:
1. Low-temperature roasting in the shell at 130°C for one hour. Peanuts roasted this way turn out perfectly crisp and easy to shell, with a naturally sweet flavour. Both a conventional oven and an air fryer will do the job. I prefer the air fryer, as I only make small batches at a time—half a jin (roughly 250g) or less. I crack them open as needed and finish them before they lose their crispness.
2. Boiled peanuts: another daily staple. This method requires pre-soaking. Keep shelled peanuts soaked in water in the fridge, and toss a few into your pot when making soup. They work well in both savoury vegetable broths and light rice water. The resulting peanuts are gently sweet and firm yet tender—a truly distinctive texture.
3. Fresh-boiled peanuts: in Fujian, peanuts enjoy a long growing season. You can scatter a few seeds in the odd corner of the land, sowing continuously from the Spring Equinox right through to Start of Autumn and White Dew. Digging them up to eat fresh can span from Minor Heat and Major Heat all the way to Minor Snow and Major Snow—a full six months.
Aside from the last option, which is a perk reserved for those living on the land, city dwellers can certainly follow suit.
Some fret over so-called experts warning that ‘while nuts are good, too many do you no good.’ But my own unsophisticated reasoning runs thus: that advice is aimed at people still adhering to the ’25–30g of cooking oil per day’ guideline. It certainly doesn’t apply to those who barely consume three grams of oil a day.
