The “Home Fridge Test” for Authenticity of Extra Virgin Olive Oil – The Reasons why it doesn’t workadmin | August 28, 2010
One of the many enduring myths surrounding extra virgin olive oil is that you can easily check its authenticity by simply putting it in the fridge and seeing if it solidifies. The myth says that if the olive oil solidifies then it’s extra virgin, but if it doesn’t then it isn’t.
Let’s firstly look at why the belief came about in the first place, and then I’ll attempt to explain explain why the fridge test isn’t a reliable indicator of extra virgin authenticity.
The myth probably arose because of two well known facts surrounding fats:
Fact 1: Extra virgin olive oil naturally consists of mainly monounsaturated fat (the legendary oleic acid). Between 65% and 85% of olive oil is made up of monounsaturates, the remaining are saturated fats (about 15-20%), with polyunsatured fats making up the last few percent. On the other hand, some seed oils like sunflower are mostly comprised of polyunsaturated fats.
Fact 2: The melting point of monounsaturated fats are much higher than the melting point of polyunsaturated fats.
The predominant monounsaturated fat in olive oil has a melting point around the fridge temperature of 4oC. That is, below 4oC monounsaturated fat is a solid, but above 4oC it is a liquid. In reality 4oC is more of a transition temperature, whereby the fat is seen as a semisolid coagulated lump. On the other hand, polyunsaturated fats melt around a super-chilly minus 30oC – as such, there is no domestic fridge that is cold enough to solidify them.
I guess you can see where I’m going with this. The myth arises because if extra virgin olive oil was purely comprised of monounsaturated fat, and if sunflower oil was purely comprised of polyunsaturated fat, and if there was nothing else in the oils which could complicate matters, then the fridge test would work perfectly every time. The extra virgin olive oil would ‘lumpify’ in the fridge and the sunflower oil wouldn’t.
But there lots of if’s there, so as you guessed, there are complications!
I used sunflower oil as the example above, but it is an extreme one as the oil contains one of the highest amounts of polyunsaturated fat. But, many seed oils actually contain quite a lot of monounsaturated fat. Canola oil for example contains around 50-60%, as does peanut oil. Some extra virgin olive oils contain only marginally more than this: 65% is the internationally accepted lower limit for EVOO. So if you put either canola or peanut oil in the fridge then both of them will solidify to some extent. So for a start, these two oils can’t definitively be distinguished from EVOO on the basis of the fridge test.
And lastly, by definition, any olive oil that has had seed oil or olive pomace oil added to it isn’t extra virgin. Most adulterated oils typically have relatively low percentages of non-olive oils in them, as the greater the dilution with seed oil, the easier the fraud is to detect. Clever fraudsters will just add enough ‘other stuff’ so as to just make it difficult for authorities to definitively say that “yes this oil is fraudulent” without having to resort to expensive sophisticated testing and lengthy court cases. An adulterated olive oil that contains 90% extra virgin olive oil and 10% canola oil will still have a high level of monounsaturated fat* and will therefore solidify at fridge temperature. Next to the authentic EVOO, it will look exactly the same.
* Here’s the math.
Assume typical values of : 100% extra virgin @ 74% oleic acid and 100% canola @ 53% oleic acid
A blend of 90% extra virgin and 10% canola will contain = (0.9*0.74+0.1*0.53) = 0.667+0.053%
= 72% Oleic acid …… not much different from the 74% in the 100% EVOO