Cork taint is one of wine’s greatest enemies, and it’s usually caused by the compound 2,4,6-trichloroanisole, commonly known as TCA. Perceptible to wine tasters at varying levels, TCA-tainted wine is identified by aromas such as mold, must, cardboard and wet newspaper. At lower concentrations, it mutes a wine's flavors. And it has led some winemakers, weary of risking corked bottles, to increasingly rely on alternative closures like screw caps. Now, a new study offers surprising insight on how TCA impacts our senses—and its findings may teach us something about cork taint prevention.
Conducted by a team at Osaka University in Japan, the study finds that rather than stimulating our sense of smell, TCA actually blocks certain olfactory channels. This blockage, according to Graduate School of Frontier Biosciences assistant professor Hiroko Takeuchi and her colleagues, creates the perception of the odor that we know as TCA. It's not that TCA smells bad—it's that it prevents you from smelling your wine, and smell is a major part of taste.
“They’re showing at a molecular and cellular level that a compound which elicits an odor never excites the cell; it only inhibits the cell,” explained Dr. Paul Breslin, a professor in the Department of Nutritional Sciences at Rutgers University and a member of the Monell Chemical Senses Center. “That’s an interesting and novel finding.”
Takeuchi expected that TCA would excite olfactory receptor cells (ORCs). “We were surprised to find that TCA actually suppressed ORC transduction currents,” she wrote in Proceedings of the National Academy of Sciences. To examine this phenomenon, the researchers isolated single ORCs from newts, who possess ORCs three times the size of humans’. By applying TCA to these cells with a puffer pipette, they observed that the compound, even in extremely small amounts, blocked cyclic nucleotide-gated (CNG) channels in the membrane of these cells—with those channels blocked, the brain doesn't receive certain signals from those cells. "It is highly likely that a single TCA molecule affects many CNG channels simultaneously," Takeuchi told Wine Spectator.
In a subsequent stage of the experiment, 20 panelists who were not experienced wine tasters participated in a double-blind tasting of white and red wines that had been contaminated with small amounts of TCA. The tasters detected musty TCA aromas at concentrations as low as 2 to 4 parts per trillion. "Even from the view point of pharmacology, [TCA] could be one of the strongest substances in the world," said Takeuchi.
But why should the obstruction of certain cell channels produce the distinct aroma of wet newspaper? It’s possible, the authors note, that humans have a receptor for TCA not present in newts. "There is a very tiny possibility that humans have a receptor for TCA," said Takeuchi. Or perhaps the suppression of CNG channels sends a signal that gets coded by the brain as an off-odor.
In fact, Breslin wondered whether the body may have evolved to respond this way to TCA, which is after all a warning that your food or drink may have gone bad. TCA can be present in a range of foods and beverages, including mineral water, apples, chestnuts, eggs, shrimp and banana peels, as well as food packaging.
The study may offer some clues about how to control off-odors, which is a top priority for winemakers and other food and beverage manufacturers. "We have raised a possibility for the mechanism of TCA effect that achieves an extremely high efficiency," said Takeuchi. "[It] may be applicable to invent novel masking agents for suppressing bad odors, and also channel inhibitors that include anesthesia and pain relief."
Breslin noted, however, that while we understand how to manipulate an odor receptor, “if [TCA] is shutting down a subpopulation of neurons, that would be more difficult to deal with.” TCA’s impact at such low levels also presents problems for effectively measuring the compound. “In this case,” added Breslin, “the nose is more powerful than human instrumentation by a long shot.”