It is the most common objection in any Swiss kitchen: olive oil is no good for frying, its smoke point is too low, use rapeseed oil or clarified butter instead. The first half of that is even true – extra virgin olive oil does start smoking earlier than refined rapeseed oil. The conclusion is still wrong, for a reason that rarely makes it into cookery lore: the smoke point is a poor yardstick for the question that actually matters.

What the smoke point is – and is not

The smoke point is the temperature at which an oil begins to smoke visibly and continuously under laboratory conditions. What burns there is not the fatty acids themselves but the small accompanying substances: free fatty acids, traces of water, mono- and diglycerides, particles of fruit pulp. The more of these an oil contains, the sooner it smokes.

That is precisely why refined oil has a higher smoke point than virgin oil. Refining strips out the free fatty acids – and with them the polyphenols, the vitamin E and the flavour. The higher smoke point is therefore not a mark of quality but the side effect of a clean-up that removed something first. What separates extra virgin from refined olive oil is set out in What Is Extra Virgin Olive Oil?

For cooking, a different property counts: oxidative stability, meaning how well an oil withstands heat without breaking down. And that depends on two things the smoke point does not measure:

  • The fatty acid profile. Extra virgin olive oil is roughly 70 to 80 per cent oleic acid, a monounsaturated fatty acid with a single double bond. Polyunsaturated fatty acids – plenty of linoleic acid in sunflower oil, alpha-linolenic acid in rapeseed oil – have two or three double bonds, and therefore two or three points of attack for oxygen.
  • The antioxidants. Polyphenols and tocopherols mop up free radicals for as long as they last. Heating consumes them – and in doing so they protect the oil.

How hot the pan actually gets

The second half of the calculation is usually skipped: how hot do you really cook at home? Not as hot as you think.

PreparationTemperature
Sweating onions, gentle stewing100–140 °C
Pan-frying160–180 °C
Deep-frying170–180 °C
Oven, roasting vegetables180–220 °C (air, not oil)
Smoke point, extra virgin olive oilapprox. 190–210 °C
Smoke point, refined olive oilapprox. 220–230 °C

The figures for the oil are ranges, not constants: a fresh oil at 0.2 per cent free acidity smokes later than an old one at 0.7 per cent, even though both may legally be sold as extra virgin. But even at the bottom of the range, the smoke point sits above the temperature of a domestic frying pan. In the oven it is the air that is hot, not the oil – the vegetables in it stay well below the 200 °C on the dial.

What the heating trials show

The most interesting data come from an Australian experiment published in 2018. De Alzaa, Guillaume and Ravetti heated ten commercial oils under controlled conditions and measured not the smoke point but the breakdown products: polar compounds, peroxides, trans fats.

The result contradicts the kitchen rule. Extra virgin olive oil performed best – better than coconut, rapeseed, sunflower and peanut oil, and therefore better than several oils with higher smoke points. It formed the smallest quantity of polar compounds and virtually no trans fats. The authors state plainly that smoke point does not predict an oil's stability under heat.

A Portuguese deep-frying trial points the same way: Casal and colleagues fried potatoes repeatedly over eight days in different oils. Extra virgin olive oil lasted longer than sunflower oil before the legal limits for degraded frying fat were reached.

Two caveats belong with this. First, both trials compare oils, not cooking styles – an overheated olive oil is worse than a properly used rapeseed oil. Second, that olive oil is more stable does not make it worth using for routine deep-frying. With a three-litre fryer, price decides.

What happens to the polyphenols

Heating costs polyphenols, and there is no way around it. Frying and deep-frying destroy roughly 40 to 80 per cent depending on temperature and time; the peppery, bitter note that comes from oleocanthal is the first to go. Anyone putting an expensive, polyphenol-rich oil in the pan is paying for something that stays in the pan.

They are not entirely lost, though. A Spanish group led by Ramírez-Anaya showed in 2015 that when vegetables are fried or stewed in extra virgin olive oil, phenols migrate from the oil into the vegetables: potatoes, aubergines, pumpkin and tomatoes afterwards contained compounds that had previously been in the oil alone. The total in the dish fell less steeply than the total in the oil. What these substances do in the body is covered in Polyphenols and Antioxidants in Olive Oil Explained.

The practical upshot: the good oil goes on the finished dish cold, the plain one goes in the pan. Both can be extra virgin.

Olive oil or rapeseed oil in a Swiss kitchen

Rapeseed oil is Switzerland's default frying oil for good reasons: it grows on the Mittelland, it is cheap, and the HOLL variety has been bred specifically for heat stability – more oleic acid and less alpha-linolenic acid than ordinary rapeseed oil. There is no argument against HOLL rapeseed oil in a deep fryer.

For the frying pan the question stays one of taste. A beetroot salad, a Zürcher Gemüse, a rösti in olive oil tastes different from one in butter – not worse, but different. Once you know both, you decide dish by dish. More on this in Swiss Recipes with Olive Oil.

Clarified butter is the third route and also stable under heat, because the water and the milk protein have been removed. Its drawback lies not in the pan but in the fatty acid profile: mostly saturated fat, no polyphenols.

How to fry properly

  • Oil into a cold pan, then heat. That way you can see when it is hot enough, and you do not overheat it in an already glowing pan.
  • If it smokes, it is too hot. Pan off the heat, oil out, start again. Once smoking begins, acrolein and other irritants form.
  • Not the top-shelf bottle. A plain, fresh extra virgin for the pan; the aromatic one for cold use.
  • Do not use frying fat forever. Two or three rounds, then discard; dark, viscous or acrid means discard at once.
  • Store it cool and dark between uses. Light and heat harm the oil with no pan involved – see How to Store Olive Oil.

Frequently asked questions

Can you deep-fry in extra virgin olive oil?

Technically yes, and more stably than in sunflower oil. In practice it usually founders on the price per litre of fryer capacity, not on the oil.

Does heat destroy the healthy compounds?

Some of the polyphenols are lost; the oleic acid remains. When frying vegetables, part of the phenols migrate into the vegetables instead of disappearing.

Why do some bottles say "not suitable for frying"?

That is the producer's advice about flavour and price, not a legal statement. An aromatic oil loses in the pan exactly what you bought it for.

Is the smoke point the same for every olive oil?

No. It falls as free fatty acid content rises and climbs with freshness. That is why an old, slightly rancid oil smokes sooner.

Sources