Olive oil pungency and bitterness

Here are a couple of interesting details to add to the story of olive oil's back-of-the-throat, peppery pungency.

In 2003, a research group at Unilever reported on the sensory effects of several of the phenolic compounds found in olive oil, including the cough-inducing substance later named oleocanthal. Oleuropein, the phenolic compound that makes the fruit of the olive bitter, is water-soluble rather than fat-soluble, so it doesn't get transferred into the oil when the fruit is pressed. But a number of oleuropein relatives do end up in the oil, and the Unilever researchers tasted them in pure form. They found these compounds to contribute mainly bitterness and drying astringency, along with some numbing, cooling, sour, salty, and tingling sensations. Relatives of pungent oleocanthal also taste somewhat astringent and bitter. So an oil rich in phenolics can have a very complex taste and mouthfeel indeed.

Other studies have found that heating olive oil reduces the levels of most phenolic compounds. And pepperiness gradually fades as an oil ages. The balance of flavors in an excellent olive oil is thus temporary and so especially worth savoring when you find it. The deterioration of olive oil is slowed by keeping it cool and protected from light.

The balance of phenolics and of so of an oil's taste depends on the variety of olive, the way the oil is pressed and handled, and on the growing conditions for olive trees--especially the water supply. The olive tree is native to the arid Mediterranean andcan get by with very little water. According to a number of recent reports, including one from the University of California at Davis, water stress produces very bitter and astringent olives, while copious irrigation produces olives and oils with very little bitterness, astringency, or fruity flavors. So the olive is another example of the many fruits and vegetables whose quality suffers when the plants are pampered.

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Andrewes, P. et al. Sensory properties of virgin olive oil polyphenols: identification of deacetoxy-ligstroside aglycon as a key contributor to pungency. J. Agric. Food Chem. 2003, 51, 1415-20.

Carrasco-Pancorbo, A. et al. Evaluation of the influence of thermal oxidation on the phenolic composition and on the antioxidant activity of extra-virgin olive oils. J. Agric. Food Chem. 2007, 55, 4771-80. http://dx.doi.org/10.1021/jf070186m

Berenguer, M.J. et al. Tree irrigation levels for optimum chemical and sensory properties of olive oil. HortScience 2006, 41, 427-32.