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  • 28 October 2020

The Science of Tasting, Drinking & Thinking Wine

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Icy Liu interviews Sam Lyons on what happens in our brain and mouth when we drink wine. 

ICY: Like many great wine friendships, Sam and mine began on Instagram.  He is a PhD student in neuroscience and is a wine fanatic.  We would meet when he would take the cheapest bus he could find from Boston to New York City, just to hunt down wines he wanted to drink.  He wouldn't even stay the night.  I learned about the neuroscience of wine tasting this year, during my enology studies at the University of Burgundy. I was fascinated by the fact that creating the taste of food and wine engages more of the brain than any other human behaviour.  I wanted to dig deeper. 

I turned to Sam to learn more.  Here is our conversation:

ICY: What actually happens from a sensory perspective when we smell and drink wine?

SAM: Drinking wine is a complex, multisensory experience, which recruits many parts of your brain.  These include sensory areas like olfactory cortex (responsible for smell) and gustatory cortex (responsible for taste), brain networks that support abstract and analytical thinking, and areas that receive information from your body and support emotional processing. The experience of wine is truly a “whole-brain” phenomenon. 

Besides your brain, your two main instruments for experiencing wine are your nose and tongue. When you sniff a wine, there are potentially hundreds of molecules travelling up through your nose, where they might bind to olfactory receptors (like a key fitting into a lock).  This could include primary odours like lemon zest (limonene) or freshly cracked black pepper (rotundone), the dough-y secondary odours emerging from lees contact, or the tertiary dried fruit aromas of aging (e.g., β-diketone in red wine). Your olfactory receptors then relay this information to your brain, which does the hard work of creating your conscious experience of smell. 

When thinking about smell, there are three functions that are worth distinguishing: detection, discrimination, and identification.  Detection is your ability to perceive the presence of an odour in a solution.  For example, humans can famously detect just a few drops of cork taint (TCA) in a giant swimming pool (which is why just a drop or two can completely ruin your wine!) However, at the same concentration, we wouldn’t be able to detect, say, diacetyl, the molecule responsible for the butter taste in some California Chardonnay.  Then, there is discrimination, which is simply your ability to say that one odour is different to another.  And finally, identification is perhaps the most challenging skill: the one that wine professionals spend years and years learning to perfect.  If you’re presented with New Zealand Sauvignon Blanc, can you name the odours as gooseberry, grapefruit, or methoxypyrazine (green bell pepper)? If someone blinded you with a salty, high-acid white wine, could you identify it as Muscadet? Or maybe it’s from the Jura? Novices have a very difficult time doing this, but fortunately this skill is highly amenable to training. Similarly, a novice of fine art may not be able to reliably identify a museum painting as Picasso or Kandinksy or Dahli, but with sufficient exposure and practice, this skill becomes automatic.

You finally take a sip. The tongue usually gets most of the credit here, with the canonical salty, sweet, sour, bitter, and umami taste buds (and maybe also watery, fatty, and metallic taste buds). The idea is similar; the molecules bind to the taste buds, which transmit this information to the primary gustatory cortex of your brain.  However, this is only a small part of the story unravelling inside your mouth.  The most important aspect of your flavour experience is actually smell--retronasal smell, that is.  Retronasal smell occurs when the flavour molecules in the wine are pushed through the back of your mouth and up to your olfactory receptors, which then send this information to the smell parts of your brain (the olfactory bulb and beyond). This process is responsible for your ability to detect black cherries, damp earth, and green stems in your red Burgundy or bruised apple and brioche in your Champagne.  Despite often being confused with taste, retronasal smell is the primary and most important contributor to flavour.

Finally, texture also plays a critical role in your wine experience.  You have a variety of different touch receptors (or mechanoreceptors) throughout your mouth that can detect changes in pressure, viscosity, friction, temperature, and more.  For example, the presence of tannin in a wine can shear the salivary coating of your mouth, which your touch receptors report as a change in friction to your brain. Your brain then represents this change as the conscious sensation of astringency. 

ICY: How does minerality and salinity fit into this?

SAM: Minerality and salinity are two of my favourite subjects to discuss, as they showcase just how complex wine and flavour science can be.

The idea of minerality is certainly controversial. Inorganic materials like limestone or slate have no smell or taste, which makes sense because they were not evolutionarily important for diet, energy or metabolism in humans.  However, certain molecules, like the sulphur compound methanethiol - found in shellfish - have been linked to wines described as more “mineral.”

Minerality has also been deployed as a descriptor of texture. Some wines might be round, others might be linear, or even blocky. This might relate to the qualities of the soil or bedrock (e.g., water holding capacity or nutrient bioavailability).  This is interesting: we often fail to use fine-grained descriptors of texture during wine tasting, so we might be missing valuable information that could distinguish between soil types. 

Nonetheless, more research is needed to confirm anything provable with regards to minerality.

Salinity – the salty aspect found in some wines - seems like it would be a straightforward case, but there is surprisingly little evidence that it is tied to actual sodium content in wine. Indeed, there is not much research on salinity in wine at all, and of the published studies, there are mixed findings.  

On the one hand, saltier soils do lead to greater sodium content in the fruit and leaves.  In one study, saline soils in Sicily led to saltier-tasting, higher-quality Nero d’Avola wines. However, in another study, the salt level of various grape musts had no relationship to their perceived saltiness. In fact, low sodium wines can still be perceived as saline, and some high sodium wines have been described as flat and insipid.  How salty tastes emerge at all is still a bit of a mystery in neuroscience, so the picture is likely more complicated than just examining sodium ions (or potassium or chloride).  A comprehensive research study on this has yet to be done.

ICY: What is predictive coding and how does it apply to wine tasting?

SAM: Psychology and neuroscience have traditionally asserted that the brain is “off” until it is exposed to a stimulus and “turned on,” causing relevant brain regions to “activate.” It turns out that this is exactly the opposite of the truth. Under a predictive coding scheme, the brain is not passive and reactive; it is active and predictive.  Instead of waiting for a stimulus to appear, your brain is constantly predicting incoming sensory information, whether at the level of the millisecond, minute, hour, day, or year. Its overarching goal is to make perfect predictions about the world.  When someone throws a ball to you, your brain is predicting where that ball will end up before it’s even thrown.  This prepares you to respond quickly and efficiently.  The more expertise you have (e.g., as a baseball player), the better your predictions will be and the more efficient your motor response. 

Predictive coding is, in my opinion, the most important neuroscience theory of the past decade.  It has revolutionized our understanding of how the brain creates the mind and offers a potentially unifying account of all brain phenomena, including the experience of wine.

In wine, predictive coding makes the bold hypothesis that flavour does not begin with your nose or tongue, but rather with predictions in your brain.  If I present to you a red wine, you might immediately predict red or black fruit flavours, moderate to high alcohol, astringency from tannin, etc.  If your predictions are correct, then your brain can process and identify those flavours very efficiently, just like a professional baseball player effortlessly catching a flyball.  However, if your predictions are incorrect, then your brain computes prediction error.  Perhaps you predicted the wine to be aged in neutral oak, but you end up tasting intense vanilla flavours instead. Your brain will take longer to process and identify these vanilla flavours because it predicted incorrectly. 

This prediction error idea plays out most (in)famously in the paradigm where wine professionals are given a regular white wine and, unknown to them, a white wine that has been coloured red.  Presumably, the wine professionals approach the red-coloured white wine as above, confidently predicting flavours of red fruit, astringency from tannin, etc.  However, what they encounter are citrus-y flavours and minimal tannin.  How should they accommodate this prediction error?  One way is to ignore it. Perhaps the wine professional is so confident that there should be red fruit, they ignore the counterevidence of citrus fruit.  This is traditionally called confirmation bias.  Another way is to heed the prediction error and update your flavour predictions to expect citrus instead of red fruit.  This is traditionally called learning.  The more confident you are in your flavour predictions, the more likely you will succumb to confirmation bias in the face of ambiguous sensory information (e.g., a red-coloured white wine).

ICY: I first came across pairing wine with music through Krug, what do we know about wine and music?

SAM: Music definitely has an impact on wine experience.  The most robust effect is fairly intuitive, which is that it can impact how much you like the wine.  If you’re listening to music that you hate, then this will impact your experience of the wine, and you might report liking it less.  This is just like if you’re having a bad day - you might not enjoy your favourite TV show as much.

Music also has the potential to change your actual flavour experience, perhaps making the wine more acidic, more astringent, fruitier, etc.  There is good scientific evidence for this effect, but how does it happen?  Well, the music isn’t literally transforming the flavour representations in your brain.  Instead, it seems to be doing something attentional.  If you are listening to music with sharp jolts of sound, perhaps this will lead you to pay more attention to the sharp “jolts” of acidity in your wine.  You’ll then report the wine as more acidic. Or maybe you’re listening to smooth jazz music, and this leads you to pay more attention to the “smooth” texture of the wine.  So, the link between music and flavour is symbolic; it depends on how the person interprets the music in relation to their wine.  This means that the same song could affect your wine experience in a different way than mine, especially if we’re from different cultures. 

ICY: How about wine and emotion?

SAM: Let’s start by asking: what are emotions in the first place? In contemporary neuroscience, emotions are thought of as predictions about sensory input from the body.  Just like how vision is created by light entering the eyes or how smell is created by molecules binding to odour receptors in the nose, emotions are created from the arising bodily input to our brains.  This could be information about changes in circulating blood glucose, blood pressure, the fullness of your stomach, etc.  This is all reported to your brain and represented as feelings of pleasure or displeasure and what’s known as activation (how energized you feel). These feelings are a fundamental feature of consciousness and are involved in all waking life (because we are never without our bodies). 

Emotional feelings are ultimately a mental representation of homeostasis.  Homeostasis is the process by which your brain and body maintain the conditions of your body most fit for survival, for example, a temperature of 37°C. Feeling good or neutral suggests that your body is maintaining homeostasis efficiently.  Feeling bad suggests that your body needs further regulation. 

ICY: So why is wine so emotional? 

SAM: Your brain predicts that it will affect your body in critical ways. This is true at multiple levels.  At a sensory level, wine tastes good, which indicates that it is potentially energy rich or nutritive.  Wine also contains alcohol, which is a potent regulator of physiology.  Additionally, it provides a context for socializing and philosophizing with other people, and other people are critical regulators of bodily homeostasis (e.g. when you vent to your best friend). Finally, if it’s your profession, it provides financial resources, which is obviously critical for obtaining the food, water, and shelter that keep your body going.

ICY: Also, are women better tasters?

SAM: Yes, but with a caveat! A recent meta-analysis of about 10,000 people showed that on average women are indeed better than men at detecting, discriminating, and identifying flavours.  However, the effect sizes are very small.  This means that if you brought 10 women and 10 men into a room, you shouldn’t reliably expect a difference between the two groups.  But if you brought 1,000 women and 1,000 men into a room, the differences should emerge.

ICY: And what are supertasters?

SAM: Supertasters are people who have high sensitivity to bitterness, sourness, and so on. This is directly related to their genetics and the density of taste buds on their tongue.  On the one hand, we might expect that supertasters won’t even like wine because it can often be bitter or sour.  Studies even show that they consume and enjoy wine less than regular tasters.  However, supertasters also show up at relatively high rates in the wine profession.  This might seem contradictory, but perhaps their initial sensitivity to taste led to further interest in food and wine and ultimately a career within that realm.  

It is often assumed that supertasters are going to be especially skilled at blind tasting. However, blind tasting largely relies on conceptual and linguistic flavour identification abilities. Supertasters may be better at detecting certain flavours, but they must still learn to describe and identify them. This is akin to a tall person who has no experience playing basketball. Their height might offer an advantage at reaching the net, but they won’t be very good at basketball without additional training. 

So, don’t fret if you’re not a supertaster!

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