Every day, as we eat our meals, we make countless judgments about what we like and what tastes good.
Yet few of us stop to consider where these sensations come from. Is flavor something we perceive through our tongues, through the aromas detected by our noses, or through the colors and visual cues we see with our eyes?
In reality, none of these senses operate in isolation. Instead, they blend together to create what we experience as “deliciousness.”
Professor Yuji Wada of the Multisensory and Cognitive Design Laboratory at Ritsumeikan University uses the methods of experimental psychology to investigate how people perceive food through their senses.
His research explores topics such as the relationship between visual appearance and flavor, the integration of smell and taste, and the ways in which perceptions of freshness and individual preferences are formed. Through this work, Wada seeks to uncover the psychological mechanisms behind the enjoyment of eating, which most of us often take for granted.
One of his findings is that what we often perceive as “taste” is, to a surprisingly large extent, influenced by smell.
How can we make the simple act of drinking a cup of tea or coffee more meaningful? How can we become more attentive to our sensory experiences? How do culture and experiences shape the smells we find pleasant? How are experiences of shikohin acquired and learned? And how might technology transform these experiences in the future? To explore these questions, we spoke with Wada about flavor, perception, and the psychology of shikohin.
Scents determine the flavor of foods
—— Today, I would like to explore the topics of taste, deliciousness, and shikohin through the lens of your research. To begin, could you tell us about your field of study?
I specialize in experimental psychology, particularly the study of human perception and the senses. Human beings possess a variety of senses, including vision and hearing. While these are often considered separate sensory systems, our experiences of seeing and hearing are not determined by each sense independently. Rather, perception emerges through interactions among multiple senses. My research seeks to understand how the brain processes and integrates information from these different sensory channels.
My particular focus is on food.
Eating is a multisensory experience that engages all of our senses. Our perception of what is delicious arises from a combination of factors such as appearance, aroma, texture, and taste. At the same time, food preferences vary greatly from person to person. Even when presented with exactly the same dish, one individual may find it delicious while another may not.
This makes the field especially challenging to study. It is difficult to identify a definitive set of conditions that will make a food taste delicious to everyone. However, through carefully designed experiments, we can begin to identify the factors that many people associate with deliciousness, as well as the sources of individual differences in food preferences.
Much of my research has focused on the role of visual information in shaping perceptions of deliciousness. At one point, for example, there was considerable interest in the effects of glossiness. Because fresh foods often have a glossy appearance, I investigated the relationship between visual gloss and people’s perceptions of freshness.
Later, I began focusing on the relationship between taste and smell. Specifically, the connection between flavor and the aromas we perceive when we exhale.
Let’s try a simple experiment. Do you have a piece of gum with you?
—— Let’s see…. I have some gummy candy.
Gummy candy is actually an excellent material for this experiment. Pinch your nose closed, then put the gummy in your mouth and chew it. You’ll notice the chewy texture, but the flavor itself will probably seem quite muted.
—— That’s true. It tastes pretty bland.
Now release your nose and slowly exhale through it.
—— Wow! The flavor changes instantly.
Many people have experienced food tasting bland when they have a cold and a blocked nose. What they’re actually losing is not their sense of taste, but their sense of smell. More specifically, the smell is not the aroma entering from outside the nose, but the aroma that travels from inside the mouth to the nasal cavity.
—— So the smell is actually coming from inside the mouth?
Yes. To better understand the relationship between taste and smell, we collaborated with a virtual reality researcher at the University of Tokyo and conducted a series of experiments. We developed a device that releases scents into a person’s nostrils in synchronization with their breathing. When a scent is released at the moment a person exhales through their nose, it creates the illusion that the aroma is originating from the back of the mouth.
Through these experiments, we confirmed that aromas perceived as coming from within the mouth can enhance the taste of the food associated with them. What’s particularly interesting is that this effect does not occur if the order is reversed.
If you smell the aroma first by inhaling through your nose before putting the food in your mouth, the taste-enhancing effect largely disappears. In other words, when the sequence of eating, exhaling, and perceiving the aroma is disrupted, the sensation of flavor becomes significantly weaker.
This is what happened in the experiment we just performed. By pinching your nose shut while chewing the gummy, you blocked the aroma from reaching your nasal cavity. Once you released your nose and exhaled, those aromatic compounds traveled from your mouth to your nose, allowing you to perceive the fruity flavor much more vividly.
—— Is it possible to experience the same thing with foods other than gummy?
It depends on the food. For example, wine sommeliers often point out that the aromas perceived through the nose and those perceived through the mouth can be quite different. Once wine enters the mouth, it mixes with saliva and changes temperature, which can alter its aromatic profile. The same is true for many foods and depending on what you are eating, the aromas released can change significantly. So not every food produces the same sensory effect.
There is an interesting example from an experiment conducted by a beverage manufacturer. Researchers found that when a wine with a high iron content is consumed alongside scallops, the fatty acids in the scallops react with the iron in the wine, producing a fishy odor. Consequently, even though each item may be considered delicious on its own, the combination can diminish the overall flavor experience.
What taste really is
—— When and how does scent influence our judgement on whether something is delicious or not?
There are various ways to classify the senses, but one useful distinction is whether a sense allows us to perceive something from a distance.
Sight and hearing enable us to detect objects and events that are far away. Smell functions similarly, allowing us to perceive odors, or chemical substances released into the air, from a distance. Before we even take a bite of food, our visual and olfactory systems help us evaluate whether something appears safe and suitable to eat.
As we saw in our earlier experiment, however, smell continues to play an important role even after food enters the mouth. When we chew, we naturally exhale while the passage to the esophagus is closed. This process carries aromatic compounds from the mouth to the nasal cavity, making it easier for us to perceive the food’s aroma.
Of course, taste and smell is received by different receptors so although flavor does not equal scent, when we are eating, we perceive taste and smell almost simultaneously, so it’s safe to say that it is essentially impossible to clearly distinguish between the two.
—— Is the combination of taste and scent what makes the flavor of food?
Yes. It is generally accepted that humans possess five basic taste receptors located on the tongue and throughout the mouth. These receptors detect the five basic tastes: sweetness, saltiness, umami, sourness, and bitterness. As research advances, some scientists have proposed additional taste categories, such as fattiness or richness, but these five remain the fundamental tastes recognized today.
With smell, however, humans are thought to have around 400 types of olfactory receptors. By comparison, dogs have roughly 800, while elephants may have as many as 2,000. In general, a greater number of olfactory receptors allows an animal to distinguish a wider variety of scents. What remains less clear, however, is whether having more receptors also means being able to detect extremely faint odors.
What we do know is that the olfactory system is far more diverse than the gustatory system. As our earlier experiment demonstrated, aroma can dramatically alter our perception of flavor. Because our sense of smell can discriminate among such a vast range of sensory information, it often plays a greater role in shaping flavor perception than taste itself.
—— So what we recognize as flavor may actually be coming from scent?
There is a classic French dish called lobster with vanilla sauce. Only a small amount of vanilla is used, and no sugar is added. Yet the aroma of the vanilla gives the entire dish the impression of being slightly sweet.
Interestingly, vanilla itself is not sweet and is actually somewhat bitter. However, through repeated experiences with foods such as ice cream, we have learned to associate the aroma of vanilla with sweetness. As a result, even when our taste receptors are detecting bitterness, the familiar scent of vanilla can lead us to perceive the overall flavor as sweeter than it actually is.
Are what we consider to be good smells innate or learned?
—— Our perception of flavor is shaped, at least in part, by our individual experiences and what we have learned over time. Moreover, even when two people eat exactly the same food, one may find it delicious while the other does not. Do you think our enjoyment of shikohin products is also something that is largely learned through experience?
That is hard to say. There are some scents that appear to be almost universally appealing, regardless of culture or upbringing. Grapefruit is one example. According to research conducted by a fragrance company, the aroma of grapefruit is consistently rated as pleasant across different cultures, age groups, and populations.
Likewise, we know that some animals are born with innate aversions to certain odors. It is therefore possible that humans also possess an instinctive preference for particular smells.
That said, there is little doubt that learning and experience play a major role in shaping our preferences. One fascinating study illustrates this using honey and babies.
As a general rule, infants have an innate preference for sweet flavors. There are several theories as to why. One is that sweetness signals a valuable source of energy, which is sugar, leading babies to instinctively seek it out. Another is that the receptors responsible for detecting sweetness are among the earliest to develop. Whatever the reason, numerous studies have shown that infants naturally consume more sweet-tasting foods and drinks. It is therefore reasonable to assume that babies instinctively associate sweetness with something pleasant.
Honey, however, presents an interesting exception. Infants under one year of age are not permitted to consume honey because their intestinal microbiome is still developing, putting them at risk of infant botulism. As a result, they do not have the opportunity to learn the association between the aroma of honey and its sweet taste until after their first birthday.
In an experiment, researchers tested babies who had just reached the age at which honey could be safely consumed but had not yet tasted it. The babies offered three drinks: sugar water scented with honey, sugar water scented with soy sauce, and plain sugar water. The researchers then measured which drink the babies consumed most readily.
If the aroma of honey were innately associated with the sweet taste that humans naturally prefer, we would expect the babies to drink more of the honey-scented sugar water. Surprisingly, that was not what happened. Instead, they consumed more sugar water scented with soy sauce.
—— So at one year of age, the babies had not yet formed an association between the aroma of honey and sweetness?
That’s right. You could also say that, at that stage, the aroma of honey had not yet become associated with the experience of something being “delicious.”
Many babies begin eating solid foods at around six months of age, and by seven or eight months it is generally considered appropriate to introduce lightly seasoned foods. If you look at commercially available baby foods, many contain small amounts of soy sauce as a seasoning.
It is therefore reasonable to assume that by the age of one, many babies have already become familiar with the aroma and taste of soy sauce and have learned to associate it with enjoyable food. Consequently, studies have shown that children between the ages of one and two tend to prefer the sugar water scented with soy sauce over either the honey-scented or plain sugar water.
—— Babies know that the scent of soy sauce tastes good.
After the babies turned one and began eating small amounts of honey, their consumption of the honey-scented sugar water gradually increased as they gained more experience with its aroma and taste. However, the increase was not large enough to substantially change the overall findings.
Had the study continued for a longer period, perhaps until the children were around three years old, the researchers might have observed a more pronounced shift. Even so, the experiment clearly demonstrated that infants do not innately associate the aroma of honey with sweetness. In other words, the connection between a particular aroma and the flavor had not yet developed.
Food preferences can be changed
—— So depending on our experiences, how we perceive scents will change?
When it comes to how we perceive smell, we cannot ignore the role of our other senses either.
Take natto, for example. I think many people would agree that fermented soybeans have a rather strong smell. That aroma is produced by a combination of volatile compounds, including pyrazines, diacetyl, and short-chain branched fatty acids. Among these, isovaleric acid is often described as having an odor similar to worn shoes.
For someone unfamiliar with natto, the idea of eating something with such a smell might seem unimaginable. Yet many Japanese people enjoy it without giving its aroma a second thought. This is because they have learned to associate that smell with a familiar and enjoyable food. Had they not grown up eating natto, they might well have found the smell unpleasant.
Consider another example. Imagine that a family member leaves an empty natto container in the sink without washing it, and you come home to find the house filled with its smell. Your first reaction would probably be that the odor is unpleasant. However, once you discover that the source is simply an unwashed natto container, your perception of the smell itself may change. You may still be annoyed with the family member for leaving it there, but the odor no longer seems quite as offensive because you now understand what caused it.
In other words, seeing the source of the smell changed your perception.
—— Visuals will also affect our perception of taste?
As I mentioned earlier, our preferences for particular tastes, aromas, and their combinations are largely shaped through learning and experience. At the same time, it is likely that these preferences are influenced not only by taste and smell, but by the integration of multiple senses, including sight, touch, and even hearing.
—— While our preferences for taste and smell seem largely determined by childhood experiences, is it possible that adult experiences change our preferences as well?
as ice cream or similar foods, the brain simultaneously activates the neural pathways associated with both “the smell of vanilla” and “sweetness.” Over time, repeated exposure strengthens the association between these two sensations.
However, these associations are not fixed. In fact, they are quite flexible. If they were rigid and permanent, it would create all sorts of problems.
Take the aforementioned natto, for example. If we have learned to associate its distinctive aroma with a delicious food, that poses no problem. But imagine if we permanently associated the smell of dirty socks with something delicious. That would obviously be problematic. Our sensory associations therefore need to remain flexible so they can be updated according to context and experience.
For this reason, I believe our food preferences can gradually change over time. Exactly what triggers those changes will differ from person to person and depend on their individual experiences. If there were a way to dramatically alter people’s food preferences, it would certainly be a fascinating subject for future research. At present, however, I think the best approach is simply to expose ourselves to as wide a variety of foods and sensory experiences as possible.
Time to redefine the meaning of shikohin
—— You are conducting various research on multisensory perception using different technologies. How do you think technological advancements will influence shikohin products and experiences in the future?
First and foremost, I believe our very idea of shikohin will change.
Take beef, for example. In the future, beef itself may come to be regarded as a shikohin product. Compared with other meats and major sources of protein, beef production has a substantially greater environmental impact, generating higher greenhouse gas emissions while requiring far more land and water. For this reason, many argue that replacing beef with plant-based alternatives, such as soy-based meat, is an urgent priority. Yet despite this, people continue to consume beef.
If we are only looking for nutritional benefits, beef consumption would not be a necessity. Yet even though we know it is bad for the environment we continue to eat it. In that sense, I think that beef has already become a kind of shikohin product. However, most people would not ordinarily think of it in those terms.
I believe we have reached a point where we need to rethink and perhaps redefine what we mean by shikohin.
—— You think we need to redefine shikohin from a broader perspective that goes beyond personal preferences?
If we are serious about addressing environmental issues, one important goal is to encourage more people to consume plant-based proteins. To achieve that, however, plant-based foods must become more appealing. In other words, they need to become more delicious.
An effective approach is through aroma.
Aromas that evoke animal-based proteins include smoked flavors, for example. If we can successfully infuse ingredients with these aromas, perhaps by developing new devices or cooking methods, I believe there is potential to drive behavioral change from animal-based to plant-based proteins.
Fattiness is another feature of animal based proteins. By recreating various sensations through various methods, we may be able to create more environmentally friendly shikohin products.
—— As ordinary consumers, what can we do to better savor shikohin products such as coffee, tea and food?
I think the most important thing is to trust your own senses.
This is something I learned during a week-long stay with Jacques Puisais, a leading pioneer of taste education in France. In his approach to taste education, he encouraged children to do two things: trust their own senses and put their sensory experiences into words.
There is no single correct answer. If a particular aroma smells pleasant to you, that’s perfectly valid. If you dislike it, that’s equally valid.
In his program, tasting was only one part of the process. Children also observed, grew, touched, smelled, and even drew the foods they encountered. Rather than simply consuming food, they learned to engage all of their senses and to “listen” to the ingredients themselves. I believe this kind of approach cultivates a deeper appreciation for food and drink.
Ultimately, the most important key to enjoying food is to trust and appreciate your own senses.
Translation: Sophia Swanson
Born in Toyama, Japan in 1990. Writer/Editor ←LocoPartners ←Recruit. Graduated from Waseda University, School of Cultural Planning. Writes for “designing,” “Slow Internet,” and other magazines. Editorial partner of “q&d. Likes basketball and coffee, and is a sucker for standing bars, snack bars, idle talk, and people who roll their own cudgels.
Editor, Writer, etc., for PLANETS, designing, De-Silo, MIMIGURI, and various other media.