Cork taint, odor suppression, and tea.

Was just listening to poet Trish Perlman interview a local wine wine consultant Dave Pohl, when they discussed cork and cork taint.* This discussion led me to look back at 2,4,6-trichloroanisole (TCA), the chemical responsible for cork taint. When I say “look back” I mean that I had tasted wine with cork taint during a class in the chemistry of wine sensory perceptions that I took at Cornell a few years ago. It struck me a pretty unpleasant—moldy, like wet newspaper.

So I decided to look for more info about TCA, and the first paper I found was quite a surprise. Takeuchi and her colleagues found that instead of actually having its own odor at very low concentrations, TCA actually suppresses our ability to sense other odors!** It didn’t work by affecting the odorant receptors directly, but by decreasing the function of the next step in odor perception, after an odorant binds to its receptor. This step involves the opening of channels that allow calcium to enter the receptor’s cell. When calcium enters the cell, the cell then passes the odorant message to the rest of the olfactory system. When these channels, called  cyclic nucleotide-gated (CNG) channels are suppressed, no message can be sent. According to Takeuchi and her colleagues, “TCA exerted a much more potent suppressive effect on CNG channels (100–1,000-fold) than other known olfactory masking agents that have been widely used in perfumery.” And the effect occurs at concentrations as low as 600,000 molecules of TCA in about 3x10^25 molecules of water (that’s 10 with 25 zeros after it! It’s also about one liter of water). Talk about a needle in a haystack!

This experiment was done in the petri dish. What about odor suppression in actual people? At what concentration does it make wine samples have less odor? At concentrations of parts per trillion. And the threshold for smelling TCA itself? 30 parts per million! 

Conclusion: even the tiniest amount of TCA can decrease the aroma of a wine, even when you don’t get off-flavors.

So where does TCA come from? It is a metabolite made by fungi from a pervasive environmental contaminant, 2,4,6-trichlorophenol. This compound is considered to be highly carcinogenic, whereas the metabolite TCA is not, so some consider the fungal transformation of TCP to TCA to be beneficial for the environment, even when it makes your wine less attractive. (Incidentally, TCA binds easily to polyethylene, so you just need your wine to make contact with some plastic wrap for a few minutes to remove the TCA***)

And, seeing that this blog is mainly about tea, with occasional excursions into discussions of wine, what about TCA in water and tea? Takeuchi and her colleagues tested green tea and tap water, as well as a number of other foodstuffs, and there it was. They found it in green tea at 5 parts per trillion, enough to suppress aromas without giving a smell of its own. As they say: “It thus seems likely that TCA degrades the olfactory quality not only of wines, but also of a wide variety of foods and beverages that have not yet been well investigated.”

Maybe we should think about drinking our green tea, or even more importantly our pu-erh, from plastic cups…

* http://outofboundsradioshow.com/shows/

** Hiroko Takeuchi, Hiroyuki Kato, and Takashi Kurahashi. 2,4,6-Trichloroanisole is a potent suppressor of olfactory signal transduction. PNAS | October 1, 2013 | vol. 110 | no. 40 | 16235–16240.

*** https://en.wikipedia.org/wiki/Cork_taint