The Oil Business

[Jenise]

Cooking oils, that is. Harold McGee's article in yesterday's NYTimes about testing the taste of oils heated to cooking temperatures is a must-read.

http://www.nytimes.com/2010/11/17/dining/17curious.html?pagewanted=2&ref=general&src=me

I was especially struck by a chilling paragraph toward the end about how the aldehydes that develop in stale oils is "toxic to our cells". I did not quite know the specifics of that. Sure, authoritarian health nazis frequently warn about avoiding "rancid oils"--usually pointing out that any oil heated to frying temperature is also considered rancid, though Harold doesn't address or corroborate that--and I guess this is why. Made me think about the kitchens of non-cooks I sometimes help in--stale/bad oil is one of the most frequent problems I run into, that off odor that's usually noticeable from an arms length away the second the cap is unscrewed. I always find it surprising that the owner of this oil neither notices nor objects to this odor, and I usually know that though I cannot stop myself from admonishing that "you need to get rid of this", that bottle isn't going to end up in the trash where it belongs.

Cooking oils, that is. Harold McGee's article in yesterday's NYTimes about testing the taste of oils heated to cooking temperatures is a must-read.

http://www.nytimes.com/2010/11/17/dining/17curious.html?pagewanted=2&ref=general&src=me

I was especially struck by a chilling paragraph toward the end about how the aldehydes that develop in stale oils is "toxic to our cells". I did not quite know the specifics of that. Sure, authoritarian health nazis frequently warn about avoiding "rancid oils"--usually pointing out that any oil heated to frying temperature is also considered rancid, though Harold doesn't address or corroborate that--and I guess this is why. Made me think about the kitchens of non-cooks I sometimes help in--stale/bad oil is one of the most frequent problems I run into, that off odor that's usually noticeable from an arms length away the second the cap is unscrewed. I always find it surprising that the owner of this oil neither notices nor objects to this odor, and I usually know that though I cannot stop myself from admonishing that "you need to get rid of this", that bottle isn't going to end up in the trash where it belongs.

McGee touches on that latter point, Jenise, when he notes that many people may view those odors as normal for oil, never having been exposed to better. The reason that aldehydes are toxic is that they react with proteins in your body. One famous example is formaldehyde, which is used to "fix" biological samples but which also is produced when methanol (wood alcohol) is consumed and which leads to blindness by crosslinking the proteins in your eye lens and clouding them over (moonshiner's cataracts). Antabuse, the anti-alcoholism drug, works by preventing proper metabolism of alcohol in the liver, leading to an accumulation of acetaldehyde in the body with lamentable results. Fortunately, people vomit before permanent damage ensues.

Having said all that, though, I seriously doubt that there are enough aldehydes in rancid oil to cause any health problems.

Mark Lipton

I very much doubt that the long-chain aldehydes produced by heating oils or fats to frying temperatures are absorbed directly into the bloodstream by the gut. The toxic formaldehyde and acetaldehyde that Mark mentions are generated inside the body, by the liver, as an intermediate in the detoxification of methanol and ethanol. Long-chain aldehydes are too large to diffuse directly into the bloodstream and cause problems. Possibly they might damage the cells lining the intestines. More likely they'll be ignored by the active transport systems that absorb lipids from the gut, and eventually will be metabolized by bacteria.

So I wouldn't worry about them.

-Paul W.