I took a wine tour on a recent vacation to Israel and listened avidly as the tour guide tried to explain what caused the dry sensation in our mouth when we sipped a nicely aged Cabernet Sauvignon. “It’s not bitter or tart,” she told us. The tannins have a taste all their own, akin to stuffing your mouth with cotton balls to remove all the moisture.
As it turns out, our brains sense the dry taste of wines — which comes from tannins in grape skins, grape seeds, and oak barrels used to age finer wines — through a completely different nerve system than our brain uses to sense the five flavors of sweet, sour, bitter, salty, and umami.
A new study reported this week in the journal Chemical Senses found that people with no ability to perceive fruity, bitter, or spicy notes in wine — due to medical conditions or temporary anesthesia that blocked taste nerves — were still able to detect its astringent dryness.
How? The German research team discovered in mice studies that the so-called “barrique” flavor in wine that causes the dry sensation excites trigeminal nerve cells; the three-branched trigeminal nerve runs from the brain through the face, detecting sensations and helping us bite and chew.
The whole system involves a rather complex signaling pathway that helps the brain sense astringency based on the amount of gallic acids found in tannins; wine aged in oak barrels tends to have higher levels of these acids, the German researchers found in previous studies, which their latest research found attaches to cell receptors in the trigeminal nerve, sending a strong signal to the brain.
“We don’t know yet which receptor exactly is responsible for the barrique flavour,” study author Hanns Hatt said in a statement, “but we are attempting to identify it.”
Wine makers have already begun to test ways to add substances like woodchips and wood flour to wines to give them a dry taste without having to spend two to three years aging them in oak barrels.
“Our research has made it possible to add the chemical substance that generates the barrique flavour directly to a wine,” Hatt said.