If you’re trying to avoid vegetable and seed oils, you’re probably substituting bacon grease, ghee, or perhaps avocado oil or olive oil. The former two can be made yourself, so you’re well aware of their content. The latter two you’ll purchase at the grocery store from dozens of options. The labels will be green and contain friendly words like “extra virgin”, “pure”, “all natural”. Savvier marketers will put a picture of a farm or something on the bottle to sell you the aesthetic of a cute, based, wholesome family farm that only cares about selling the best and purest oils to the most conscious consumers.
Turns out, like pretty much any marketing campaign, it’s generally a lie. Two researchers out of the UC Davis Food Science and Technology Department did a thorough chemical analysis of samples of avocado oil from online and local grocery stores and found all to be adulterated in some sense (mostly with soybean oil), and most to be oxidized to the point of rancidity before reaching the expiration date on the bottle.
How did they look at the avocado oils?
The researchers collected 14 samples from 6 grocery stores, 8 samples from 2 online sources. They didn’t mention specific brand names, but claim to have covered all “major brands”. Since they were submitting to an academic journal, they wouldn’t have been permitted by the editorial board to reveal brand names. This is quite common across all scientific and technological fields.
They tested the free fatty acid content via gas chromatography. The free fatty acid content is a common measure for oil quality–we seek a lower free fatty acid content. These free fatty acids contribute to the rancidity of oil and are linked to inflammation and obesity. The researchers found that refined avocado oils had a free fatty acid content under 0.1%, while “extra-virgin” oils had a large range (0.03%-2.69%). The authors attributed the high FFA values for the extra-virgin oils to the use of poor quality avocados or poor handling (such as overheating) during processing.
Peroxide values were also calculated to measure products of oxidation of the oil. This was intended to measure the quality in a culinary sense. Oxidation of oils produces “off” flavors. Again, they found the refined avocado oils performed best of the samples, but still did not meet other standards for quality proposed in food chemistry literature.
For purity, they looked at a fatty acid profile. They measured the content of various fatty acids, and found that many of the samples fit the profile for soybean oil. The authors were careful to only suggest “economic adulteration” (diluting with soybean oil) as a cause, since there are almost no commercial standards for the quality of avocado oil.
What can a consumer take away from this?
So what do we do with this information? We can create some common sense shopping rules for avocado oil based off this paper and its findings.
- Cost: If it’s too cheap, it’s probably adulterated. The authors noted that the soybean oil was found in the samples that cost around $0.50/fl oz. Other extra virgin avocado oils are marketed closer to $1.75/fl oz.
- Packaging: Ignore anything in a clear bottle. Oils are very sensitive to photo-oxidation (which makes the oils go rancid). Dark green glass bottles are probably best. One of their samples was packaged in a tin bottle. I don’t know if this is acceptable packaging for avocado oil, but an article from the Olive Oil Times mentions that dark glass and stainless steel are best for olive oils, while tinplate “needs more research”. I’d be willing to extend the same standards to avocado oil.
- Color: This one is a minor consideration, since it’s measuring the chlorophyll content of the oil. The cited literature reports a very wide range of chlorophyll content and notes that the variations in color can be due to a number of factors including the cultivar, fruit ripeness, extraction methods, and storage. Ideally you’re looking for a greener avocado oil.
- Labels: Labels mean next to nothing. The authors’ findings suggest that the refined oils were less likely to be heavily adulterated, but the refining process strips most of the Vitamin E content from the oil. The Vitamin E content is certainly desirable for cosmetic purposes, and may be wanted for nutrition purposes as well. But “extra-virgin”, “virgin”, “pure” are all useless labels. They were all found to be at least partially adulterated.
- Taste: I assume almost everyone has eaten a good avocado. The best ones are buttery and grassy. The oil should smell and taste like this as well. If there’s either no smell or a “plastic” or “playdough” smell, it’s rancid.
- Expiration Date: The authors were a bit confusing on this aspect. All of the oils they tested were well within the acceptable window, yet they still found plenty of evidence of degradation. It stands to common sense reasoning that you should avoid oils close to their expiration date; they’ve likely been stored for far too long. All this will help with is rancidity.
Other Comments and Notes
I tried to do the typical internet search for “best avocado oils”. Perhaps this is my incurable cynicism talking, but most of the reviews struck me as press releases, so I’m not going to make any recommendations on brands. I don’t personally cook with or use avocado oil, so I can’t speak to any of the brands. If any of you can recommend something based on extensive personal use, I’ll update this article with reader suggestions.
A website called “ConsumerLab” claims to have done a full test on 7 named brands of avocado oil. They require a paid membership to view the results, so I declined. My guess is the generic Aldi brand and Whole Foods brand would be ones to avoid for sure. (Don’t sue me, Jeff Bezos. It would be like squeezing blood from a stone.)
Personally, I use olive oil for lower heat cooking (or just eating), coconut oil for baking, and animal fats for all other high-heat cooking (ghee, butter, lard, goose fat, bacon grease). I haven’t found a need for avocado oil in the kitchen, but for those who do, buyer beware.
- Green, H. and Wang, C.. First Report on quality and purity evaluations of avocado oil sold in the US. Food Control. 2020;116 https://doi.org/10.1016/j.foodcont.2020.107328