The Nose Knows

Ever gotten a whiff of a tainted bottle of wine? You pop the cork and instead of ripe berry notes and velvety toasted oak, a waft of damp mustiness greets your nostrils. Scientists have known that TCA, or 2,4,6-trichloroanisole, is the pesky chemical responsible for spoiled wine but new research has just uncovered what you actually smell—or don’t smell—from a tainted bottle.

It has been widely assumed that TCA interacts with your nose in the same way most other odorants do. Tiny smelly molecules usually bind to receptors in your mucous membrane and excite your olfactory nerve cells which tell your brain what you smell. However in a recent publication from Osaka University in Japan, scientists say that in fact TCA is not exciting your olfactory neurons at all. Instead TCA gets inside of your nosey nerve cells and prevents other odorants, like the ones that make your wine smell fruity and delicious, from being detected.

One clue to the authors’ conclusions is the exceedingly low concentration of TCA required to stop olfactory signals. Experimental evidence showed that even solutions of TCA with 600 molecules per milliliter could halt the sensory pathway—much fewer than would be required to physically block all of your smell receptors. If TCA were in fact binding to your smell receptors and telling your brain “oh that smells musty,” it would take way more than 600 molecules because (a) only a fraction of the molecules that enter your nose actually bind to a receptor at all and (b) a huge majority of receptors would need to be blocked to prevent detection of other smell-inducing molecules. But why do we care what TCA does in our noses?

It turns out odor masking agents like TCA are already used in perfumes to help cover up the unpleasant chemical smells of all those, well, chemicals. Many products that are advertised as “unscented” actually just contain a chemical like TCA that masks the other smells. I can also imagine several situations where a chemical that masks odors could be useful, like around my garbage can or in a port-o-potty. Now that we have a few clues about how TCA works maybe it will be applied to these smelly situations.

That being said, I personally think cork taint is a more pertinent problem than stinky trash cans. Think of all the wine that is going to waste! It has been shown that fungi that naturally reside on cork are at least partially responsible for producing TCA but they aren’t making TCA just to watch us wrinkle our noses. They are making it as a defense mechanism. TCA is largely non-toxic both to us and to fungi, but the molecule that it is made from, 2,4,6-trichlorophenol, definitely is not. A fungus that is living with toxic 2,4,6-trichlorophenol nearby will work really hard to convert it to non-toxic TCA. And while it may be easy to say, “just kill the stupid fungi!” that might leave us with a bigger problem than off-smelling wine. 

Perhaps there is some way to break down the TCA into less potent molecules, or a way to strip the cork of TCA precursors before it’s used to plug a bottle of wine. In the meantime producers and consumers will both still curse TCA-ridden wine, but at least next time you pop a tainted bottle you’ll know more than your nose knows. 

Sources and further reading

Maria Luisa Alvarez-Rodriguez, et al. (2002) Cork Taint of Wines: Role of the Filamentous Fungi Isolated from Cork in the Formation of 2,4,6-Trichloroanisole by O Methylation of 2,4,6-Trichlorophenol. Applied and Environmental Microbiology 68 (12) p. 5860-5869.

Hiroko Takeuchi, Hiroyuki Kato, and Takashi Kurahashi. (2013) 2,4,6-Trichloroanisole is a potent suppressor of olfactory signal transduction. PNAS, published ahead of print September 16, 2013, doi:10.1073/pnas.1300764110.

L. Maggi, V. Mazzoleni,  M.D. Fumi and M.R. Salinas (2008) Transformation ability of fungi isolated from cork and grape to produce 2,4,6-trichloroanisole from 2,4,6-trichlorophenol. Food Additives and Contaminants: Part A (25)3, p. 265-269.