The Bitter Truth About Olive Oil

by Darya Rose | Mar 18, 2009

Olive Oil and Balsamic Vinegar

Have you ever had homemade hummus turn out bitter? Have you whipped up your own batch of mayonnaise and found an unpleasant aftertaste? Or are you just confused about why I warned against putting olive oil in a blender for my harissa recipe?

The culprit behind these bizarre phenomena is extra-virgin olive oil, which is very sensitive to mechanical agitation. Upon one reader’s request, I set out to explain the unusual behavior of this common ingredient.

But getting to the bottom of this problem was not easy. The internet is teeming with false assumptions and unfounded hypotheses about why olive oil can become bitter when blended. Most people point their finger at the quality of the oil itself, accusing the chef of using a cheap brand that was bitter before they included it in their recipe. I knew this wasn’t true because it has happened to me several times, and I always use excellent olive oil.

Another common hypothesis is that “heat” caused by the friction of high-speed spinning blades makes the “delicate oils” in the olive oil turn bitter. This explanation makes even less sense, because as most of you know olive oil can be heated in a pan to several hundred degrees and does not burn or turn bitter. There is no way the oil gets hot enough to go rancid after a few seconds in a blender.

The only logical and (mostly) scientific explanation I found for the bitter olive oil phenomenon was from Cook’s Illustrated. I am inclined to trust this source because they essentially run their kitchen like a laboratory, which gives them major credibility points in my book. Also, their reason offers a plausible, mechanical explanation that does not depend upon the quality of the oil itself. I have not seen the data with my own eyes, however, and they do not cite their sources.

According to Cook’s Illustrated, extra-virgin olive oil is the only kind of oil susceptible to becoming bitter. Even pure olive oil can handle blending better than the extra-virgin kind. The reason is because extra-virgin olive oil contains a high percentage of molecular compounds called polyphenols (thought to be cancer-fighters), which are normally coated in fatty acids. Under standard conditions, the fatty acids in the oil prevent polyphenols from dispersing in an aqueous environment. This is because oil and water do not mix.

When these fat molecules are broken into droplets in an emulsion, however, the polyphenols are distributed into the solution and their bitter taste can become apparent. When the emulsion is only lightly blended, the bitterness is not perceptible. But a blender or food processor breaks the droplets down into smaller sizes, increasing polyphenol dispersal. These suspended polyphenols can ruin an otherwise delicious recipe.

The easiest way to avoid this problem is to use either pure olive oil or a different kind of oil altogether, such as canola or safflower oil. Alternatively, if you would like to keep the rich taste of extra-virgin olive oil you can hand whisk your emulsion rather than using a blender. Just be careful not to over work the mixture. You can also start your recipe by blending a small amount of stable oil (e.g. canola), then hand whisking your extra-virgin olive oil in at the end.