I Taste Red

Jamie Goode

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Summary of some studies and facts around the science of wine. Dense enough so that you’ll learn something, but Goode makes it accessible even without a chemistry background. Great start into a deep dive on wine tasting (and especially valuable when paired with a glass of wine :)


Synesthesia is the remarkable phenomenon in which stimulation of one senory modality is registered as the perception of another sense…The key aspect of synesthesia that makes it different from the sort of crossmodal experiences normal to all is the fact that the sensory stimulus (the inducer) reliably elicits not only the normal sensory experience, but also an inappropriate sensation (the concurrent). Overall, there are thought to be some sixty different types of synesthesia, but the most common form is when the sensation of particular colors is associated with written or spoken letters, digits or words.

One of the issues is called the “binding problem.” Within the brain, different aspects of sensory experience are represented in widely distributed areas. Even for a particular sense, different features may be represented in separate areas. In vision, for example, shape, motion, color, and size are all registered initially in separate areas of the brain. Yet we experience these widely spread bits of sensory information as a seamless, unitary perception. The question of how they are brought together is the so-called binding problem.

In one experiment, the authors invited fifty-four subjects to describe a real white wine and a real red wine. A few days later, the same group had to describe the aromas of the identical white wine and a “red” wine that was actually the same white but colored red with a neutral-tasting food colorant. Interestingly, subjects described the true red and the “red” wine in similar terms (this was shown statistically), even through one of the wines was actually white. Their perception of taste and smell was influenced by the color. Vision has more of an input in the wine-tasting process than most people would think.

Charles Spence at the University of Oxford has carried out research to determine what people believe influences their perception of flavor identity and intensity. “It turns out that one of the reasons why red coloring (as in the study by Morrot et al) turns out to be such a powerful driver of what we experiences (both in terms of smell and taste) is that redness typically equates with the ripening of fruits in nature.”

In another study (2003), Jay Gottfried and Ray Dolan showed that visual cues can help people identify smells, when the picture matches the smell. For example, if people are shown a picture of a double-decker bus at the same time as being given a sniff of diesel fumes, they can recognize the diesel fumes faster. In contrast, if there is a lack of congruence between a picture and a smell, the performance is slower: an example here would be a picture of a fish and the smell of a cake.

It is possible to argue that we have two senses of smell, as Gordon Shepherd does in his book Neurogastronomy (2013), where he makes a distinction between the sniffing-in smell (orthonasal olfaction) and the smell that comes around the back of the mouth when we breathe out (retronasal olfaction).

If chemicals that are very different structurally can smell quite similar, and chemicals of very similar shape can smell very different, what is the explanation? Turin’s exciting but controversial ideas is that instead of recognizing shapes, olfactory receptors are recognizing the electrical resonance vibration of molecules…If we have 400 different functioning olfactory receptors, how do we discriminate among thousands of different smells? This is a really interesting question, and the answer seems to be that it is all about pattern recognition.

So while we may be amazed at how good dogs are at smelling, we should not automatically think that they are better than us. We are probably more reliant on retronasal olfaction and on the contribution this makes to discerning flavor, and, as a result, this is something we are very good at. We cannot compete with dogs when it comes to picking up traces of scent when we walk through our local park, but once we have food in our mouths, we are rather expert.

They found that both whiskey lactone and isoamyl acetate acted simultaneously on single olfactory receptor nuerons. This confirms that the responses of receptors to mixtures is not the result of the simple sum of the effects of the individual compounds. That is, there is an interaction among odorants that often occurs at the level of the receptor itself. Adding whiskey lactone to isoamyl acetate partially suppressed in the olfactory receptor activation for isoamyl acetate alone, but in some mixes it can actually enhance the association.

While desensitization is problematic for wine tasting, cross-adaption is a greater hazard. If there is a recurring or prolonged smell in the tasting room, people become desensitized to that smell. It might be a wine component, or in might be an environmental smell, such as coffee, paint fumes, or cooking smells. But if the smell is a wine aroma, this will change your perception of the wine without you being aware of it. Tasting a lengthy flight (or serious) of the same kind of wine can be risky in this regard.

Taste receptors are spread more or less evenly across the tongue. This may come as a surprise to anyone familiar with the tongue map beloved of school biology texts, which shows sweet, salty, bitter, and sour flavors to be localized to different regions. This map is based on a German study from the early twentieth century that showed very small differences in sensitivity to the different tastes around the perimeter of the tongue. An influential translation of this study in the 1940s wrongly assumed that where sensitivity to the different tastes was at a minimum, it was absent altogether. The result? A diagram showing that bitter, salty, sweet, and sour are detected in distinct regions. Despite being quite wrong, it is still widely taught to students of wine.

Anyone who has undergone dental work that has modified the inside of their mouth in some way will know that we are very sensitive to changes in the mouth environment: we have a very well-developed sense of touch, and the tongue is especially good at exploring the inside of the mouth and helping us to map it mentally in great detail.

Tannins are formed by plants as defense molecules, defending against microbial attack and also acting as antifeedants. Plants are extremely vulnerable to being eaten as they are literally rooted in place, and so they have evolved to make themselves unpalatable.

We find the bitter taste and astringent sensation of tannin aversive, and as with all such unpleasant oral sensations, the aversion can protect us from harmful consumption. Thus the PRPs and HRPs are potentially filling two roles: allowing us to detect tannins in food and to reject the food if the concentrations might be dangerous, and also helping to neutralize any tannins present in food to be ingested.

Astringency is not principally a taste, in the sense that it is not one of the primary taste modalities of sweet, sour, bitter, salty, and umami. Instead, it is chiefly detected by the sense of touch in our mouths…Dietary tannins entering the mouth are bound by proteins present in saliva and form precipitates. These proteins include the PRPs and HRPs, whose role is to carry out this binding and protect us from the potentially harmful effects of tannins in inhibiting digestive enzymes. Also involved is another important protein type in saliva: the mucins. As mentioned earlier, these are involved in forming a lubricated, slippery protective layer over the internal surface of the mouth. Tannins remove this lubrication, causing a sense of dryness, puckering, and loss of lubrication in the mouth. This is what we describe as “astringent.”

With red wine, the challenge to the palate is the repeated exposure to tannins. With white wines, the tannic content is much lower, and the challenge will be acidity, which is usually much higher than in red wines (that is, the pH of whites is lower).

He gives the example of Denis Martin, whose restaurant in the Valais, Switzerland, has two Michelin stars. It is located in the middle of a knitting museum, and Martin saw that when people walked through the door, they were not going to enjoy his modern Swiss cuisine fully; they are uptight, suited Swiss businessmen dining on expense accounts. The solution? People are told to arrive at 7:00 p.m. and there is nothing on the tablecloth except for a toy Swiss cow. Nothing happens until someone picks up the cow and it moos; before long, the restaurant is filled with the sounds of laughter and mooing cows. Changing the mood, this is a psychological palate cleanser, preparing people for the meal to come.

Rolls and others have shown that it is in the orbitofrontal cortex that taste and smell are brought together to form the sensation of flavor. Information from other senses, such as touch and vision, is also combined at this level, to create a complex, unified sensation that is then localized to the mouth by the sense of touch – after all, this is where any response to the food or drink, such as swallowing it or spitting it out, must take place.

Smell objects are created through learning by what is called synthetic processing. This is where we learn to recognize combinations of smells that occur together. These objects might also include information from other senses, such as taste and color, and also “affective” input (how much we like or dislike them)…This is very similar to what occurs in vision.

What we do when we try to examine a wine as professionals is to fight against our understanding of wine as an object. We are trying to distinguish individual components in a complex mix, and that is quite difficult, because it is not how our sense of smell normally works. Our sense of smell, as we have discussed, is tuned to recognize patterns that we can then treat as smell objects.

It seems that the sommeliers were experiencing something different to the average person when they tasted wine, just as fMRI studies on musicians have shown that music activates different areas of trained musicians’ brains to those of casual listeners. “There is clear evidence that the neural connections of the brain change with training and experience,” says Castriota-Scanderberg.

Unsurprisingly, there was a correlation between price and liking. Significantly, subjects preferred wines one and two when they were told they were drinking the higher-priced wines. The brain scans, comparing the response of subjects when tasting the sames but believing them to be different and at different prices, showed that the parts of the brain that experience pleasure are more active when subjects think the wine is higher priced. The price is not just affecting perceived quality – it seems to be affecting the actual quality of the wine by changing the nature of the perceptive experience.

Sweetness in wine is a combination of three factors. First of all, there is sugar itself. This is sensed by sweetness taste receptors on the tongue. Second, there is a sweetness that comes from fruitiness…The third source of sweetness is alcohol itself, which tastes sweet.

Bartoshuk explains that the PROP compound and its chemical relatives contain molecules that stimulate a specific bitter receptor in the taste membrane. Nontasters of PROP carry two recessive alleles of a gene that has recently been localized to chromosome 7; tasters carry either one or both alleles. “My lab discovered a large variation among tasters; those with the most taste buds are called supertasters and those with fewer are called medium tasters,” says Bartoshuk.

In one study, Pickering and colleagues looked at 331 wine drinkers and classified them as experts (111) and consumers (220). The PROP taster status of all of them was ascertained, and PROP bitterness sensitivity turned out to be higher among the wine experts than the consumers. The team concluded that people might self-select themselves for the wine profession on the basis of their sensory ability: if you are more sensitive to flavor, you may be more likely to become a wine professional.

For the student of fine wines, these observations mean that there is no “single truth” about a wine. While much of the quality of fine wine can only be appreciated by experience and learning – a realm that is accessible to almost all – the existence of specific anosmias and aguesias means that, at the most basic level, the same wine is not the same to all people. We do indeed live in different taste worlds.

If they made us ill, this linking of the senses would help us to avoid repeating the experience. If they tasted good and did not make us ill, all was well. But what if they did not taste good, and did not make us ill? If we could acquire a taste for this sort of food, we would benefit significantly. Further, if we and our kind could accept this food while others did not, we would have more of it to ourselves. Thus, evolution has always driven us to appreciate acquired tastes.

If Prescott and colleagues are right, people will only like more those elements of a wine’s aroma that they are actively looking for. This could reinforce the importance of having a wine vocabulary. Mere exposure probably does not have any effect in people who drink wine without thinking about it.

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