Olive Oil Refrigerator Test

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The Olive Oil Conundrum

I have a relative in California who grows olives and sends me a case of his olive oil every year. As I expected, in the fridge this olive oil turns into a thick semi-solid. An oil like olive oil, with its high content of monounsaturated fatty acids and low level of polyunsaturated fatty acids can be expected to be liquid at room temperature and semi-solid when chilled.

Then another friend sent me a bottle of her olive oil—authentic olive oil from one-hundred-year-old mission olive trees. Imagine my sur­prise when I discovered that the oil remained a liquid in the fridge! It didn’t noticeably thicken at all, yet I knew it was pure olive oil.

RANGE OF OMEGA-6

This mystery sent me scouring the Internet, where I found a 2021 article from Spain, “The Oleic/Linoleic Acid Ration in Olive (Olea eu­ropaea L.) Fruit Mesocarb Is Mainly Controlled by OeFAD2-2 and OeFAD2-5 Genes Together with the Different Specificity of Extraplastidial Acyltransferase Enzymes.” The upshot of this long title: the amount of omega-6 linoleic acid in olive oil can vary greatly, from just over 3 percent to as high as 27 percent! (See Table 1.)

Most tables list the omega-6 content of olive oil at 11 percent because that is a typical read­ing of the Arbequina variety, one of the most common olive cultivars. This is in line with the omega-6 content of lard and palm oil. But at the upper level of 27 percent, the composition of olive oil is similar to that of sunflower and canola oils! (See Table 2.)

The researchers attribute the fatty acid profile of each cultivar to genetics rather than climate and other environmental factors, but one analysis found that the omega-6 content of the Arbequina variety could range from 7.2 percent to as high as 23 percent.

Olive oil contains mostly monounsaturated oleic acid and saturated palmitic acid—these are the two fatty acids that could be expected to cause the oil to jell in the fridge. But the amount of these two fatty acids can vary greatly. Oleic acid can range from 55-83 percent, and palmitic acid from 7.5-20 percent.

Note that these values have nothing to do with the oil’s “authenticity.” The North Ameri­can Olive Oil Association (NAOOA) states that “An often perpetuated myth related to olive oil is the ‘Fridge Test”—a supposedly simple home test for olive oil authenticity.” This is indeed correct. While it is important to purchase au­thentic olive oil, even extra virgin olive oil (not processed with chemicals or heat), these labels do not tell you whether or not the oil has a low omega-6 content and high monounsaturated and saturated fat content.

TESTING

We sent twenty-four samples of olive oil to OmegaQuant laboratories in Sioux Falls, South Dakota for testing. The results are shown in Table 3.

 

As expected, there was a range of values for polyunsaturated omega-6, from 4.2 percent to as high as 15.86 percent. The total of saturated and monounsaturated fatty acids ranged from 90.47 percent to 78.08 percent. We created an index by dividing the total percentage of stable saturated and monounsaturated fatty acids by the percentage of omega-6 fatty acids (Column E divided by Column F), which ranged from 21.55 (best) to 4.92 (worst).

THE FRIDGE TEST IS NO GUIDE

Imagine our surprise when we found no relationship between the jelling qualities of the olive oil and the index. For example, the olive oil with the best index (sample 14) did not jell at all, while the samples with the lowest index jelled within two weeks, and the sample with the worst index (sample 24) jelled within a week.

We do not have an explanation for this discrepency—it may have to do with the presence of polyphenols, or with the arrangement of fatty acids in the triglyderides—but obviously we cannot use the “fridge test” to determine the quality of olive oil. We will have to rely on laboratory testing.

The good news is that most of our samples tested at 12 percent omega-6 or below (about the level found in lard, a fat traditionally used in cooking). We will continue our testing program and include only those brands that test at 12 percent omega-6 or below in the shopping guide. If you have a brand you would like for us to test, please send a small bottle to the Foundation.

This article appeared in Wise Traditions in Food, Farming and the Healing Arts, the quarterly journal of the Weston A. Price Foundation, Fall 2024

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