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An aunt of mine went to some sort of nutrition lecture course and claims to have been taught that using cold-pressed oils in frying would produce certain chemical compounds which are toxic to humans. Of course she wouldn’t remember the exact chemicals or other details. Is this claim true?

(I fried with cold-pressed oil a few days back not knowing the difference, and I’m fine.)

  • You might need to search for a more notable source to keep the question alive. I'm sure there must be someone who makes this claim in public. – matt_black Aug 12 '12 at 19:08
  • I would also say that "I'm fine" isn't really relevant (and may even be inaccurate) for this question. The type of damage claimed from consuming trans-fat isn't the kind of damage you would notice until you've had a heart attack, developed late-onset diabetes, obesity, or been tested for early warning signs of similar chronic diseases. – Flimzy Aug 13 '12 at 2:14
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Once you realize that there is, no such thing as risk free living, so everything is dangerous. This becomes a question of how dangerous is it to use cold pressed oils in frying.

Cold pressed oils aren't a kind of oil, they are a process for extracting the oil.

Cold Pressing is a natural physical process used to extract vegetable oils from oilseeds such as Canola and Safflower and nut oils from the likes of almonds and walnuts. These oils are extracted from seed by a simple crushing and filtering process. There is no heat or chemical treatment so the oil is essentially unchanged.

This differs from the way that oils such as corn oil are extracted today, using a chemical solvent like Hexane, which is later distiller out of the oil.

Historically, cold and hot expression methods were used. These methods have largely been replaced with solvent extraction or pre-press/solvent extraction methods which give a better oil yield. In this process the oil is extracted from the oilseed by hexane ...

Still though, some oils are still extracted by the cold press method.

Olive, peanut and sunflower are among the oils that are obtained through cold pressing.

There isn't anything in cold-pressed oils that isn't in their chemically extracted equivalents, so the only danger is from the production of cancer causing chemicals when the oils begin smoking. Here is a chart of some of the common smoke points of cooking oils, and a graph.

You will note that sunflower oil has a much higher smoke point than extra virgin olive oil. Typically, the normal frying temperatures are between 325-375 degrees Farenheit (163-191 Celcius). The frying temperature is very new the smoke point of extra virgin olive oil, but below regular olive oil. If you didn't notice any smoke coming off of the frying pan, you are probably completely safe (from cancer causing smoke, and the formation of aldehydes). Even if you did consume or inhale the smoke from the frying process, you chances of getting cancer from that one exposure are extremely low.

  • You talk about cancer-causing smoke. Do you have any references for this? Is it the acrylamides in the olives, or something else? – Oddthinking Aug 13 '12 at 4:55
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    @Oddthinking, newly linked – user1873 Aug 13 '12 at 5:25
  • Actually, this EPA report has me worried that acrolein may not cause [cancer 4.7] (epa.gov/iris/toxreviews/0364tr.pdf#page=101). Originally, I thought that it might be a problem because of other studies, like the chinese cooking SHS study, and this link about (possibly not peer reviewed) olive oil – user1873 Aug 13 '12 at 5:46
  • To add to the answer: The smokepoint is mostly based on how refined the oil is. The oils that are sold as 'cold pressed' are usually also refined very little resulting in a low smokepoint. Best seen in the 4 olive oils listed in the reference. – Stefan Aug 13 '12 at 19:50
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    @user 1873 actually based on Wikipedia it still holds. Sunflower oil - Unrefined - 225°F. It doesnt make much sense to refine cold pressed oils as that removes flavors. (compare cold pressed virgin olive oil taste to refined 'extra light') And flavor is the major reason why to use cold pressed oils in the first place. tl;dr Cold pressed: for salads, Refined: for frying – Stefan Aug 14 '12 at 17:00

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