This is how the story goes. You bought an unfamiliar brand of extra virgin olive oil. As usual, you keep it in the fridge because this is what you have learnt to. After few days, and in a week, you notice nothing happen. Based on your “understanding” of a good quality extra virgin olive oil, you started to wonder, later ponder, and then question, “Is this a genuine extra virgin olive oil?” And your conclusion is …
For a start, the purpose of storing extra virgin olive oil in the fridge is not so much to “fridge test” the olive oil for its authenticity, but rather to reduce the rate of oxidation.
In other words, we are trying at best to retain or at least not to lose too much of the Polyphenols in the extra virgin olive oil, which are the antioxidants we need for good health.
Tip: Fridge storage is normally for extra virgin olive oil.
There is one issue in storing extra virgin olive oil in the fridge.
Once the bottle is opened, and we constantly take the bottle out and into the fridge, the air that is trapped inside the bottle would likely be condensed inside the bottle, and this effect might cause the degradation of the olive oil.
Hence, in our routine interactions with visitors during our olive oil tasting road shows conducted at Duke Bakery outlets, we will always advise our visitors to keep their premium quality extra virgin olive oil at room temperature in a cool dark place away from light and heat if we are using it on a regular basis, because condensation eventually might affect the aroma and taste of the olive oil.
Tip: If we are using our extra virgin olive oil regularly, there is not necessary to store it in the fridge.
The other reason people store olive oil in the fridge is to test the authenticity of the extra virgin olive oil.
The term used is called “fridge test”.
Fridge test is one of the many misconceptions that we have with extra virgin olive oil – that is, many people believe that authentic extra virgin olive oil, when placed inside a fridge, will become cloudy and solidified.
Fridge test is not a reliable way to determine whether an extra virgin olive oil is real nor whether its quality is good. Very often, adulterated extra virgin olive oils pass the fridge test.
Here are the reasons why.
The solidification of extra virgin olive oil when placed inside a fridge is due to many factors.
For the beginning, one is due to the presence of the (1) monounsaturated fat (oleic acid), and (2) wax content.
MELTING POINT (or FREEZING TEMPERATURE) of MONOUNSATURATED FAT
According to a chemistry textbook, the melting point of monounsaturated fat is around 13-14°C. The melting point is the temperature at which it changes state, from solid to liquid.
However, when the researchers at the University of California at Davis conducted a fridge test with different grades of olive oils and other seed oils at 4°C, high quality extra virgin olive oil only started to show solidification when it was placed in the fridge for five days, but it never fully solidified.
On a separate experiment, Dr John Deane, an internal medicine specialist in Marin County, California, USA, put several olive oils in the freezer with a thermometer to determine the actual freezing temperature.
The melting and freezing points are approximately equal. Small differences between these quantities can be observed.
He found that at 4°C, most of the olive oils had not hardened or formed any crystals. At 2°C, most were firm enough that they could not be poured but were as soft as butter at room temperature. He observed that as the temperature lowered, more components of the oil solidified. At -12°C, the olive oils were hard enough that a fork could not penetrate them.
We run a simple “fridge test” experiment ourselves. Here are the timeline and outcomes:
01 Oct 2015, 10am – Fridge test started. A bottle of extra virgin olive with 1/3 full was placed inside a fridge where vegetables and other daily products are stored (not the freezer side where ice is made.)
03 Oct 2015, 9am – Small particles were seen inside the bottle – the beginning of the solidification.
03 Oct 2015, 10pm – Evidence of thickening process happening inside the bottle.
04 Oct 2015, 9am – The olive oil inside the bottle has become “cloudy” or “milky”.
05 Oct 2015 – The olive oil becomes condensed.
The fridge test is under the following conditions:
– Fridge is 20% full.
– The temperature is pre-set at 3/5 of the pre-set range.
– The bottle of extra virgin olive oil is 1/3 full.
One thing to note: The premise behind this fridge test around the melting point (or freezing temperature) is the assumption that extra virgin olive oil is purely (100%) comprised of monounsaturated fats.
The fact is: The percentage of monounsaturated fat in extra virgin olive oil varies according to the type of olives used to extract the oil. The range can be from 65 to 80%.
Hence some authentic extra virgin olive oil needs lower temperature or longer period to be solidified – or be seen thickening and clouding.
Second note is: Other compounds that are present in the olive oil and the processing method also play a part.
The processing method such as “winterised”, i.e. chilled and filtered the wax content out of the olive oil, would cause an authentic extra virgin olive oil fail the fridge test, and would only become slightly thick (but not solid) when frozen.
Finally, in order to achieve and keep a consistent flavour profile, some producers may blend several varieties of extra virgin olive oil.
The result of the extra virgin olive oil is commonly called coupage. This will also affect the time and the level of cold required to get to the solidification stage.
WAX CONTENT in Extra Virgin Olive Oil
The surface of the olive has a coating of a thin naturally produced wax. When olives are extracted into oil, the wax ends up in the oil.
Different olive varietal produces different amount of wax. The climate, hot or cold, where olives are grown, also play a part – When the weather is hot, more waxes produced than cold.
While the amount of wax in an olive oil is small, the presence of it is a contributing factor or act as a seed for things to solidify in a cold environment.
Many adulterated extra virgin olive oil pass the fridge test because it is a blend of extra virgin olive oil and refined olive oil or olive pomace oil. Since refined olive oil and olive pomace oil have a higher wax content, so it solidifies when placed in the fridge.
For information: The wax content of the extra virgin olive oil, by the International Olive Council’s requirements, must be less than 250 mg/kg. While olive oil is less than 350 mg/kg, and olive pomace oil is more than 350 mg/kg.
Tip: The lesser the wax content in the extra virgin olive oil, the better its quality.
Richard Gawel, an experienced olive oil consultant taster, illustrated with two examples why fridge test is not a reliable mean to determine the quality of the extra virgin olive oil.
He first put across his point saying that by putting Canola oil, which contains around 50-60% monounsaturated fat, in a fridge, it will solidify to some extent, but Canola oil is not extra virgin olive oil.
He further illustrated by showing that 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.
If fridge test is not a reliable mean to determine the authenticity and quality of an extra virgin olive oil, then what is a better way?
The colour of the extra virgin olive oil can be enhanced by adding chlorophyll to make it greener. The solidification of olive oil can be easily duplicated by adding more wax content. Adulterated extra virgin olive oil (mixing with cheaper seed oil or olive pomace oil) can be seen solidified in the fridge.
But it is more difficult to replicate the aroma and taste of a premium quality extra virgin olive oils, which contain fruitiness, bitterness and pepperiness, the latter two are due to the presence of the antioxidants and anti-inflammatory compounds (Polyphenol and Oleocanthal).
How to select and buy a premium quality extra virgin olive oil?
Instead of using fridge test or looking at the colour of the olive oil, we should:
- Find out the chemical quality parameters – at least read the Acidity level (Free Fatty Acid) – the lower the better;
- Smell the aroma and taste the extra virgin olive oil to detect bitterness & spiciness in it besides the natural fragrance or fruitiness of the extra virgin olive oil.
IN SUMMARY: All olive oils will be eventually solidified in a fridge because of the presence of the monounsaturated fat and the amount of the wax content in it.
When the fridge is cold enough, the melting point (or freezing temperature) is reached, the olive oil will change its state – from solid to liquid or liquid to solid.
It is a matter of time and coldness because our fridge may be more full or more empty. The amount of olive oil used for fridge testing is certainly another key factor in determining the time required for the olive oil to solidify.
Tip: Buy award-winning extra virgin olive oil that has consistently won awards at major international extra virgin olive oil competitions – at least we are sure that this olive oil has been tested and endorsed by the Olive Oil Master Tasters in the various competitions it has participated in.
Some Important Information to Look Out For When Buying Extra Virgin Olive Oil.
For all of our extra virgin olive oils, we have listed the Harvest Date, Best Before Date, the Chemical Quality Parameters, including the wax content, among others, to help us make an informed decision. You can find them here at buyoliveoil.vas.com.sg.
We have also written an article listing the 8 Tips to Choosing & Buying Premium Quality Extra Virgin Olive Oil to help us sift through the many choices of extra virgin olive oils that are available in the market.
Photo: flickr. Rishi Bandopadhay. Midnight Snack. CC License.