Transcript: The True Shelf Life of Cooking Oils
When you look at a bottle of oil in the grocery store, there’s a “best-before” date, advising consumers how long they have to consume it before it starts going rancid, and builds up oxidation products that can be particularly harmful to human health.
Here are the best-before dates for eight culinary oils: almond oil, avocado oil, hazelnut, macadamia, grapeseed, rice bran, toasted sesame, and walnut oil. These are the best-before dates in numbers of months, counting from the day the oil is made.
So, if you made a batch of walnut oil on January 1, 2012, the best-before date printed on the bottle from that batch would be 12 months later—January 1, 2013. Now, this is making some pretty strict assumptions. This is assuming you are keeping the oil in the refrigerator in a airtight, dark container, so it’s not exposed to air, room temperature, or light—particularly after it’s opened.
Now, these scientists were skeptical that the companies were printing accurate dates. And so, they put all the oils to the test to find out what the true expiration dates were. Would it match what the companies say? Would the companies put a longer duration, trying to make the oil appear more stable than it really is? Or, would they put a shorter duration, trying to encourage people to buy their product more frequently?
For rice bran oil, the company said seven months. And actual estimated shelf life found in the tests? 6.5 months. Not bad, pretty close. In some cases, though, the truth was stretched one way; in others, it was stretched the other way. Look at almond oil. They said it would last over a year, and it really only stayed good for three months. And remember, that’s three months in the fridge, in the dark—and after production, not after when you buy it.
Macadamia and walnut oil were the real outliers, though. Mac oil lasted longest; over a year. The company totally undersold its stability. But for walnut oil, they said a year, and it only lasted about two and a half weeks—according to rancidity testing with the “Rancimat.”
To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Kerry Skinner.
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