March 6, 2014
Photo Credit: Gola Are e Scienza del Gusto 2014
Recently, I was asked to organize an evening on food and the brain as part of Gola – the Art and Science of Taste at the Trinennale di Milano. This blog post is based on the entry I wrote for the exhibition catalogue. The talks and tastings for the evening were presented by the neuroscientist, Charles Spence, a Co-I on the AHRC project, Re-thinking the Senses, the food artist, Caroline Hobkinson, the philosopher and Co-I on Re-Thinking the Senses, Ophelia Deroy, and the chef-researcher, Charles Michel, and myself.
When we taste food we think that we are getting all the information about the dish’s flavor from our tongues, but this is not the case. What we call tasting always involves a combination of touch, taste and smell: the feel and temperature of the food in the mouth, the aromas reaching the nose, these too contribute to the perception of flavor. Even before you engage touch, taste and smell, you will often select what you want to eat with your eyes, assessing it by how it looks. At the same time, there may be sounds of a wine being poured and as you eat you will hear the crunch of raw vegetables or salad leaves. In all these ways, your senses are activated when you eat or drink; and the way the brain integrates the information from these different sensory inputs ensures that the experience of tasting is always multisensory.
To understand just how multisensory the experience of eating and drinking is, it’s important to recognize how little the tongue contributes to tasting. Receptors on the tongue code for the basic tastes of sweet, sour, salty, bitter, to which we can add umami (or savouriness) and metallic. Perhaps we have receptors for fat, or at least fatty acids. But that’s all we get from the tongue. And yet think of all the flavours described by philosopher of aesthetics, Frank Sibley:
‘ripe mangoes, fresh figs, lemon, canteloupe melon, raspberries, coconut, green olives, ripe persimmon, onion, caraway, parsnip, peppermint, aniseed, cinnamon, fresh salmon’. We don’t have receptors for these items. There are no chicken, beef, or tomato receptors, and so our ability to taste these flavours depends on more than taste alone. Notice, too, that we cannot construct these flavours from the basic tastes:
Coconut may be somewhat sweet, and lemon sour or acid, but what other tastes combine with sweetness to give coconut, or with sourness or acidity to give lemon? How could one construct a blend of distinguishable tastes…to yield that of coconut, or lemon, or mint? Try to imagine a recipe: ‘To make the flavour of onion (or pepper, or raspberries, or olives), add the following [basic tastes] in the following proportions . . . ’ (Sibley 216-7)
There is no such procedure, and yet we can all perceive the flavours Sibley describes. This is because of the role smell plays in creating the experience of flavors. This is not smell as we ordinarily think of it, where odours we inhale from food or wines reach the nose before eating or drinking. Instead, we are talking about a sense of smell that neurophysiologts have drawn our attention to, which is activated when odours travel from the mouth to the nose during chewing and swallowing. This is known as retronasal olfaction and it is often experienced by the individual as a taste occurring in the mouth. To this we must add the contributions of touch that enables us to assess a food as creamy or oily, sticky or crunchy. And then there is the chemical irritation of the trigeminal nerve in the face that spices bring about. These interactions between the senses of touch, taste and smell give rise to our flavor experiences; and as the psychologist Martin Yeomans says:
Arguably, multi-sensory integration may be at its most extreme in the case of flavour perception since few other experiences offer the opportunity for concomitant stimulation of all the major senses
So, when tasting wines, we respond not just to taste sensations on our tongues, which provide information about salt, sweet, sour, bitter, savory, or metallic, but to the integration of these tastes with fruity and floral aromas. This is put together with the velvety, silky, or satin textures of the wine, or the slight astringency of the tannins. Food tasting can also evolve and the spiciness that excites the trigeminal nerve, causing mint to feel cool in the mouth and mustard to feel hot.
Think of what happens when you taste menthol. You experience a minty aroma, a slightly bitter taste and a cool sensation in the mouth. Take any one of these elements away and you no longer have the experience of menthol.
Such combined flavor perceptions are multisensory, and multisensory perception is the rule and not the exception in sensory experience. The case of flavor perception provides one of the best examples. The brain has to integrate the relative contributions of taste, smell, texture, and trigeminal irritations to arrive at a unified perception of flavor. The result is a complex interaction effect that takes effort to appreciate, since the components are often inseparable in our experience. What is more, tasting is not a single experience; it has a dynamic time course, and by slowing it down, one can appreciate what is happening at each moment, from the sweetness of the attack as the wine enters the mouth, to the gentle notes of bitterness in the finish. How complex and satisfying a wine is will depend on sensory and temporal properties that can go unnoticed at first by novice tasters.
It is unsurprising, when so much is happening in the mouth and nose, that tasting judgments can diverge. But this doesn’t mean they are idiosyncratic or inexplicable, nor that they are subjective and independent of the flavors foods and wines have. Differences may be due to the sensitivity of our tongues. Some people have many more, and more densely packed, papillae, or taste buds, on the tongue. These are super-tasters who are highly sensitive to bitterness, or sourness. The taste buds of other people may be sparse and far apart and this will lead to much reduced sensitivity. In some sense , we live in different taste worlds. People also show different sensitivities to odour compounds and to touch, with different thresholds for those sensitivities, and this may lead to large individual differences between tasters’ experiences of the same foods and wines. Nevertheless, tasting is an experience that puts a taster in touch with the sapid, odourous and textural properties of a food’s or wine’s tastes or flavors. These properties need to be discovered, whatever our individual tasting equipment is like; and while we need food science to study the molecular chemistry and physics of foods and liquids, we also need neuroscience and psychology to study the science of the taster.
The wider study of taste and tasting is beginning to reveal fascinating insights into how our preferences for foods and wines are shaped not just by our physiology but also by background factors such as lighting and music as well as expectations set by sight and sound. It is these factors and their effects on multisensory perception that are studied by my colleagues at the Centre for the Study of the Senses, who work with chefs and artists to advance the science and create better tasting experiences. In one set of experiments, psychologist Charles Spence provided participants at Feran Adria’s laboratory with the same strawberry mouse served on black plates and white plates. What he discovered is that people found the same dessert up to 10% sweeter when eaten off a white plate. This is just one way in which the plate on which a dish is served can contribute to how we taste it. In another set of experiments conducted in London, drinkers were give a glass of the Singleton whisky to sample. As they wandered from room to room, with the same glass in hand, the whisky tasted differently because of changes in the lighting, the colours of the walls, or the ambient sounds. These effects can be used to re-create the special atmosphere that accompanies the eating of dish or the drinking of a wine that made the whole experience so pleasurable. A perfect example is the signature dish at The Fat Duck restaurant in Bray, called The Sound of the Sea..
The dish is the creation of three Michelin star chef Heston Blumenthal working with Charles Spence from Oxford’s cross-modal lab to create the perfect sonic accompaniment to fresh seafood. Diners are presented with a plate of seafood on a sand-like bed of grains with strips of seaweed, while at the same time being given a conch shell containing an iPod and a set of earphones. Though the headphones, they listen to the sound of the sea, focusing their attention on the food and it’s origin, to enhance the experience of eating fresh fish. In another of Blumenthal’s creations diners are served with bacon and egg ice cream, and on the plate is a piece of crispy friend bread, which diners were asked to eat with the ice cream. What happens is that in the mouth, the flavor of the bacon appears to migrate to the sensorily appropriate, crispy fried bread leaving the egg flavor with the smooth ice cream. This reflects the brain’s attempt to make sense of the appropriate match of texture to flavour, and it provides clues about the complex mechanisms that drive multisensory perception.
We are just beginning to unlock the secrets of taste and flavor and food by drawing on research from many disciplines, and it is by working together with anthropologists, neuroscientists, chefs, artists, and food and drinks manufacturers, that we will advance the science of tasting, and, hopefully, create better tasting experiences for us all.
This blog post was written by Professor Barry C Smith as part of his role as the Leadership Fellow for the AHRC Science in Culture Theme. The Science in Culture Theme is a key area of AHRC funding and supports projects committed to developing reciprocal relationships between scientists and arts and humanities researchers.
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