Detecting rancidity in oil

[Fat Guy]

Okay, so when you talk to people who make oil their business the thing they always say is that most of the oil out there in the stores is rancid. Now with olive oil I think I can tell when it's gone very rancid, but that's just a general impression I get. Ditto for walnut oil, where it seems pretty apparent. With other oils, though, I have no idea what I'm looking for. Can anybody help with some good descriptions of the taste/aroma of rancidity in various kinds of oil? I have so much oil lying around I'd love to go through it and eliminate whatever isn't good.

[Steve Plotnicki]

Cold pressed virgin olive oil should be used within a year of it being pressed and bottled/tinned. Whether it goes rancid after a year is another matter. I've seen cans that have, and I've seen cans that last much longer. But usually two years is the limit and I can smell the deterioration in the oil. Can't speak for other kinds of oils. I once had a friend schlep a bottle of walnut oil back from the Dordogne. It was poured into the bottle while he waited. It was only supposed to last for 120 days, but we used it for years. It was the most amazing oil I ever tasted.

[Fat Guy]

There's an anecdote in the latest Rare Wine Co. olive oil newsletter about opening a bottle of 1988 Il Poggione olive oil, without detecting a hint of oxidation or rancidity. Amazing how this stuff varies.

[Shiva]

Easy. Just run over to Home Depot and pick up a near infrared spectroscope.

[mamster]

I find it very easy to tell with "neutral-flavored" oils such as canola, at least by taste. A dot of even mildly rancid canola oil on the fingertip is not a taste soon forgotten. In general, though, buy high-turnover oil from a trusted source and keep it out of the light; if it doesn't taste weird to you and your guests, you don't have a problem.

[ngatti]

I find it very easy to tell with "neutral-flavored" oils such as canola, at least by taste.  A dot of even mildly rancid canola oil on the fingertip is not a taste soon forgotten.  In general, though, buy high-turnover oil from a trusted source and keep it out of the light;  if it doesn't taste weird to you and your guests, you don't have a problem.

Yeah I was thinking the same thing. Kinda like pornagraphy. You may not be able to describe it, but you'll know it when you see (in this case, taste) it.

Nick

[Jim Dixon]

Here's how I understand the rancidity issue (and I'm not a food scientist)...

Polyunstaturated fats oxydize readily (oxydixation = rancidity), especially when exposed to heat or light (and, of course, oxygen). The majority of edible oil sold is refined and subjected to high temperatures in the process, leading to some degree of oxydation. These same oils are also deodorized. Some researchers believe that refined oils arrive at the market with a certain degree of rancidity, but it's not the gross rancidity that you can detect by taste.

Expeller-pressed oils can become rancid more quickly and should be kept in the refrigerator. So-called 'cold-pressed' oils may have been heated to temperatures near 200 F (there's no legal definition of the term), so they may also be more susceptible to oxydation.

Extra virign olive oil made from less ripe fruit has high levels of polyphenol compounds that are natural antioxidants and will slow the rate of oxydation (generally, the more 'peppery' the oil tastes, the higher the polyphenol content), and doesn't need to be refrigerated unless you keep it around for a long time.

Jim