The “Home Fridge Test” for Authenticity of Extra Virgin Olive Oil – The Reasons why it doesn’t work
admin | August 28, 2010One 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
Hi Richard,
Thanks for this! FWIW, I’ve never seen canola oil even begin to congeal in the fridge — perhaps because of its high content of omega-3 alpha linolenic acid, which is even more desaturated than linoleic.
Do phytosterols not play a role in the issue? Real EVOO should contain a significant amount,while refined OO would have been winterized to remove them — no? USDA says olive and hazelnut oils both have 120 mg/100 g, but I’m assuming that this is more likely refined than EVOO; and canola and soybean oil have zero.
Hi once again
You’re right. I’ve noticed that some types of oil don’t solidify when theoretically they should. Solidification of complex mixtures of substances (like all edible fats are) is a very complex matter. Scientists still argue today about crystal formation in water! But in some ways this adds to my arguement that trying to predict what is in a complex substance by simply looking at its freezing point is a dubious practice.
Re the phytosterols. I actually don’t know. But I have noticed that oils made from varieties which are high in waxes tend to solidify more easily and sometimes they don’t like to fully melt either. But that is just an observation.
Come to think of it sterols might not be that important in this. Seed oils are much higher in sterols that EVOO (even though they are refined). Corn oil is the highest in this respect (from memory). I guess you could try to see if corn oil solidifies in the fridge! My guess is that it won’t or not much anyway.
RG
Uh, sure, but if the olive oil doesn’t turn solid in the fridge, can’t we still safely assume it is not pure olive oil? We may not know if the opposite is true (solid in fridge means pure) but we know the former is true (liquid in fridge means not pure). No?
[…] For the full Slick Extra Virgin Blog posting on this topic, please click HERE ← Previous […]
[…] oil is real by putting it in the fridge; if it solidifies, it’s real. Not necessarily . This isn’t a reliable test. Mono-unsaturated oils solidify in the fridge, while polyunsaturated oils don’t, but oils are […]
Paul: No, you can’t. Some olive oils can have as little as 55% monounsaturated fat, and lots of linoleic acid (a polyunsaturated fat), similar to soybean oil: olive oils made from the Arbequina (a popular one for California oils), Chemlali, or Chétoui cultivars (the later two being the dominant ones in Tunisia) are especially prone to low monounsaturated fat levels. Unless they also have a lot of waxes, these oils probably wouldn’t freeze up. And a friend of mine in the olive oil business recently did an experiment where she put a very high-oleic-acid (83%) oil into the fridge, and it didn’t freeze up, for reasons not known: maybe the very low level of saturates, maybe a very low level of wax.
– Thanks Olivechirper – I couldn’t have said it better myself. RG
Olive oil is a natural product, made from >700 different varieties of olives, each with their own characteristics, grown under different conditions, picked at different levels of ripeness, and processed differently. There are just too many variables affecting waxes, fatty acid ratios, and the distribution of these into triglyceride structure to make the fridge test reliable as a positive or negative screen for authenticity (let alone quality).
I understand. So what to do? Switch to coconut? I really don’t want to be consuming GMO corn and canola.
Hi Paul
Where are you from? Despite all the bad publicity, most extra virgin olive oil is authentic. The best thing to do is find someone who makes it, and buy from them directly. Most of the fraud in this business occurs when the supply chain is long, as it is easier to do the nasty, and harder to identify when it happened, and therefore who did it.
RG
[…] We’ve all heard countless times that extra virgin olive oil is the core of the Mediterranean diet, and extremely healthy. But how solid is the science surrounding olive oil? Medical pundits frequently hold forth about olive oil with faulty facts. How often have you been warned not to cook with extra virgin olive oil because heat breaks it down – despite the fact that quality extra virgin olive oil actually has a very high smoke point, and is extremely healthy? Who saw Dr. Oz, in an otherwise fairly useful segment on olive oil real and fraudulent, urge his viewers to use the “fridge test” to find out whether their olive oil was authentic? (The fridge test is based on bad science, and doesn’t work, as explained by chemist Richard Gawel here.) […]
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