Remember the previous two posts, where I discussed an article about wine liking and the effects of cheese on liking?* There was one wine, in particular — Madiran — that had high astringency, and was relatively disliked compared with other wines used in the study, and disliked even more with each successive sip. Cheese significantly decreased the progressive dislike, and I attributed this change to the effects of fat in the cheese. Here I reconsider this proposition.

Tannat grapes used in Madiran — wines made from these grapes in France have an extra high tannin content. Image from Wikipedia.

Friend of Pairteas and wine expert Tim Hanni MW pointed out to me the other day that he had tried the experiment of evaluating wine astringency with and without olive oil, to test the notion that astringency could be diminished by fat. He found that olive oil did nothing to diminish astringency, and suggested that the effect of the cheeses on wine astringency that I discussed in last week’s post was due to other factors in the cheese, such as salt and sourness, and not due to the fat content. In fact, as he found, you can diminish wine's astringency by taking a pinch of salt and then sucking on a lemon before drinking your wine. I've seen this process in action and it really works.

This observation got me thinking about the very complex system of trigeminal and taste activation. 

First, how do tannins interact with the trigeminal receptors to create the sensation of  astringency? 

Tanninns have to bind to both bitter receptors and TRPV1, the trigeminal hot receptor, simultaneously. If they are displaced from either of these receptors by another compound your won’t sense astringency. 

So what do salt and lemon juice do in this regard?

With respect to salt, it activates a specific part of the TRPV1 receptor, and changes its conformation. The following is speculation on my part, but it is likely that the salt, by activating the TRPV1 receptor in its way, bumps the tannins off their binding site, so the can no longer cause astringency. Further, salt inhibits the ability of bitter sensitive taste bud cells to send on their message, providing another way for the sensation of astringency to be blocked.

Second, lemon juice contains compounds that interact with bitterness receptors, acid receptors, and cold receptors (TRPA1), so it can act through each of these pathways to influence astringency. By interacting with bitterness receptors, lemon juice can bump tannins off the bitter attachments they need to create the astringency sensation. Next, the pathway for bitterness sensation acts through cells that respond to citric acid. If these cells are activated by sufficient amounts of acid, the message they send will be dominated by sourness rather than bitterness, so astringency will be inhibited. Finally, when you activate TRPA1 you inhibit TRPV1, the trigeminal receptor needed for astringency sensation, so here you have yet another way in which lemon juice could decrease astringency.

Why didn’t olive oil work to decrease wine’s astringency? As we noted before, fats do inhibit TRPV1 activity, so one would expect an effect—after all, you can turn down the heat of capsaicin with some fatty food. Two possibilities come to mind. 

One possibility is that the part of TRPV1 to which tannins bind is not affected by the presence of fat. It is worth noting that there is good evidence that capsaicin binds to a different part of TRPV1 from salt—changes in the DNA of TRPV1 that increase capsaicin heat are in a different place in the resulting TRPV1 molecule from changes in the DNA that affect salt sensitivity. So the notion that tannins might bind a different site in the molecule from fat is not unreasonable.

The second possibility has to do with olive oil itself. Good quality olive oil (and Tim would be sure to use the best!!) is astringent all by itself, plus it contains bitter compounds, as well as oleocanthol, which activates another trigeminal receptor, the cold receptor TRPA1—activation of this receptor gives you the catch in your throat when you take in really good olive oil. That catch feeling may augment the aversive sensations rather than decrease them. 

That said, one thing is quite clear: if you don’t like bitterness and astringency in your wine or your tea, add a tiny bit of salt and some lemon juice, and violà — deliciousness prevails!

* Mara V. Galmarini, Anne-Laure Loiseau, Michel Visalli, and Pascal Schlich. Use of Multi-Intake Temporal Dominance of Sensations (TDS) to Evaluate the Influence of Cheese on Wine Perception. Journal of Food Science Vol. 81, Nr. 10, 2016. doi: 10.1111/1750-3841.13500.