Transcript: The True Shelf-Life of Cooking Oils
When you look at a bottle of oil in the grocery store there are “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, grape seed, rice bran, toasted sesame, and walnut oil. These are the best-before dates in number of months, counting from the day the oil is made. So if you make batch of walnut oil on January 1st 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 based you are keeping the oil in the refridgerator in a airtight, dark containiner, so it’s not exposed to air, room temperature, or light, particularly after it’s opened.
This group of scientists were skeptical that the companies were printing accurate dates, and so they put all the oils to the test to find out that the true these expirations 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 on, to encourage people to buy their product more frequently?
For rice bran oil the company said 7 months. Actual estimated shelf-life found in their 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 stays good for 3 months, and remember that’s 3 months in the fridge, in the dark, and after production, not after when you buy it.
Macadamia oil and walnuts were the real outliers though. Mac oil lasted the longest —over a year, the company totally undersold it’s stability, but for walnut oil, they said a year and it only lasts about 2 and a half weeks, according to 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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