 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 8 culinary oils— almond oil, avocado oil, hazelnut, macadamia, grapeseed rice, brantoza, 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 in January 4, 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're keeping the oil in the refrigerator in an 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? I mean, 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. Oh, not bad, pretty close. In some cases, though, the truth was stretched. One way and others have been stretched the other way. Look at almond oil. They said it would last for 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 the 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 ransomat.