Or is it just hokum? The importance of the sense of smell in informing our taste is a subject that fascinates biologists. Most high school biology texts include an experiment designed to test just how important our sense of smell is in how we taste things. The experiment involves peeling and cutting up apples, potatoes, onions, and/or celery into bite sized pieces and then blind-folding people and having them taste the pieces at random with their nose plugged so they cannot smell.
And the fascinating result? Nobody can tell the difference between apples, potatoes, or onions when their nose is plugged! Isn’t that amazing? It would be if it were true, but, if you do the experiment with at least ten people you will find that only a few have any trouble at all in quickly telling an apple from a potato. And the onion? They are going to be pissed at you for tricking them into munching on a piece of raw onion. The couple of people here and there, if you find any, who have trouble, well, you have to ask yourself the next obvious question: What if you tried it with them just blind-folded but their nose unplugged? See, some people just have very bad palates.
I tried this experiment without the onions. I left out the onions because I already knew that, despite what some people have claimed, the texture is not similar at all to apples and potatoes, and most people can pick out the texture difference between those as well. The result was that ALL FIVE of my subjects, who were friends thinking I had become even weirder than usual, readily identified the apples and potatoes. I know that five is not a large number of subjects, but in this case we only need one person to disprove the claim. On the other hand, you’d need many, many more to prove it if people routinely were unable to tell the difference. But that is not what happened.
Now these were not just any apples, mind you, they were honey crisp apples, which may just be the best tasting apples for eating that ever existed. I guess I could have went with a bland tasting apple. But, that is called stacking the deck. Apples have much more taste than raw potatoes.
This experiment is often done in grade school science class on children, whose sense of taste is less developed. As adults, we are harder to fool.
Of course, the sense of smell does influence the sense of taste. But when you read things like “Your sense of smell controls 90% of your sense of taste,” this is pure fabrication. Likewise you may read that “aroma comprises 75% of your perception of flavor.” Don’t buy it. No matter what source you check, in fact, you’ll get a different number. That is because the numbers are made up by scientists wanting to sound “proofy.” Whether they are deluding themselves as well as deceiving us is sometimes hard to tell.
Those who want to convince us that the sense of smell is is more important than taste must have never smelled Limburger cheese. To me, as to others, the smell of this soft, white cheese is reminiscent of stinky feet: it is pungent and revolting! Yet, if you taste it, you might find that the flavor is better than the smell. So, either some people think that stinky unwashed feet have a good flavor, or, there is a bit more going on and smell isn’t such an overriding arbiter of our sense of taste. Or is it flavor? I’ll get to that.
When it comes to perceiving apples from potatoes with my nose plugged and my eyes blinded, I have no problem. An apple is clearly an apple and a potato is clearly a potato. But it is definitely true that the apple tastes more bland without smell. And the more bites I take with my nose plugged, the blander it becomes. Likewise, I’ve plugged my nose while eating spicy Thai food, and it definitely tasted quite bland, in comparison to the taste with my nose open. But I’m not going to mistake it for Italian.
Usually, the importance of smell is completely exaggerated and there is no way to put such a precise number on anything having to do with taste. So, any figures about how much of this or that controls your taste are usually completely made up. Even statements such as “the majority” of what you taste is controlled by smell, have no basis in fact because we simply do not understand well enough how the brain processes flavor. Moreover, ALL the senses are involved in our perception of food. For instance, if a potato chip sounds crispy when you eat it, you may very well think it tastes better than a chip that sounds less crispy. And, in fact, a chip that falls short on the crunch factor, as far as the noise it makes, may be perceived as tasting stale, even if it is actually quite fresh. Notice in this paragraph that I said flavor and not taste. There is the detection of flavors and there is “taste” and these are not necessarily the same thing.
Taste and flavor are very individual and subjective experiences. It is pretty much impossible to assign such precise statistics to something derived through subjective experience. Imagine how studies to determine the importance of the sense of smell would have to be carried out. Experimental subjects would have to “rate” the taste or flavor of something in some way. How salty is the food on a scale of one to ten? How much more bland is the food on a scale of one to ten? Just looking at salt, you can imagine that the ratings of the subjects would be quite variable, as different people are more or less sensitive to salt.
And look at what we mean when we say salty. Plain salt, right out of the shaker, is salty. That is because it is highly concentrated when we taste it that way. But a food that has just the right amount of salt (for us) will not be deemed to taste salty but simply to taste good. Only when too much salt is added do we declare it salty. And how much salt is too much varies among individuals. As you get older, you may tend to want more salt. With that, let’s go into the sense of taste a bit.
The sense of taste is also called gustation. Despite the hoopla surrounding presentation, texture, smell, etc. (all of which are important), taste is, and will always be, the most influential factor in food selection. You taste food via your taste buds. Have you ever wondered why they were called buds? It’s because the arrangement of their cells is similar to the shape of a flower. These cells are arranged in clusters and are neuron-like epithelial cells. Your taste buds are on the underside, back, sides, and tip. There are not any taste buds on the main, flat and middle part of your tongue. Did you realize that? Not only that, but there are taste buds on the palate of the mouth and in the pharynx.
We used to think that different areas of the tongue contained taste buds that were more sensitive to one type of taste. According to this early information, the tip of the tongue is more sensitive to sweet and sour tastes, the sides are more sensitive to salty and sour tastes, and the back is primarily sensitive to bitter tastes. However, we now know that all of the areas of the tongue that actually contain taste buds are usually sensitive to more than one taste. More updated information shows us that the front of the tongue is sensitive to sweet, salty, and bitter and the side of the tongue is sensitive to sour.
There is a fourth kind of taste, called unami, which in Japanese means “delicious.” Unami is pretty much analogous to savory. This taste is really amino acids called glutamates. You’ve probably heard of monosodium glutamate. Well, this produces an unami taste. Imagine the taste of beef broth without salt, and you get unami. There is lots of fancy science having to do with amiloride-sensitive sodium channels for salt taste, depolarization by hydrogen ions blocking voltage dependent potassium channels for sour taste, G protein-linked receptors coupled to the cAMP second messenger system for sweet taste, and a metabotropic glutamate receptor for unami. Whatever any of that means.
We know that the sweet taste has to do with the chemical configuration of certain simple carbohydrates like sugars, glycols, alcohols, and aldehydes, but we understand how this taste works very little. The salt taste comes from ionized salt like the familiar sodium chloride and other salts found naturally in foods. Sour tastes come from acids, which are substances that have lots of hydrogen ions in them like natural fruit acids (think lemons), vinegar, and some vegetables. A food that has fermented through biological action (gone sour) will also be acidic. Too much sour, then, is a signal to us that a food has gone bad. But a little sour is a good thing and we tend to have a love/hate relationship with it. If you’ve ever sucked on a fresh lemon, you may have experienced simultaneous revulsion, as your mouth puckers up, and a certain thrill at the sheer intensity of the sensation.
The bitter taste is similar. It comes from some compounds that are quite frequently dangerous too us. This is why a bitter taste, if it is too strong or concentrated, is off-putting to us: it serves as a warning that the food may be poisonous. However, a bit of bitter can be perceived as a good thing, as well, and we humans have developed a “taste” for it. These bitter compounds are things like caffeine or theobromine. Those are bitter alkaloids. We can handle a good bit of these, but they can poison us if we consume too much in a short space of time. Other bitter alkaloids, like those found in the Deadly Nightshade family, are even more dangerous. Regardless, bitter is still an important part of the our total experience of a food’s taste.
In order for a taste bud to “taste” something, it must be dissolved in liquid or saliva. When you put food into your mouth and chew it, bits of it are dissolved in saliva and this saliva, with volatile and nonvolatile compounds from the food dissolved in it, collects in the central pores of your taste buds, called taste pores, forming little pools. This saliva comes into contact with cilia (microvilli), which are small hair-like projections of the gustatory cells. These receptor cells send signals to the brain via a cranial nerve, either the facial, vagus, or glossopharyngeal nerve. The brain translates the electrical signal into a sensation that we perceive as taste. Realize that, as with any sense, without the brain to translate the signals, we wouldn’t taste anything.
Although above I described five tastes, unami does not seem to be detectable by everyone and not everyone agrees that it is a distinct taste. It was discovered by a century ago by a Japanese chemistry professor at the University of Tokyo named Kikunae Ikeda.
Ikeda observed that the dominant taste of Japanes dashi, a soup, was clearly distinct from the other four tastes. He set about painstakingly isolating the compound responsible for the distinct taste of Japanese dashi, which turned out to be glutamic acid. It is true that the taste of unami is hard to detect. One reason for this is that it tends to be accompanied by salty and sour tastes. I think it’s fair to say the the four others are a bit dominant, but, in case you think the “jury is still out” on the existence of unami, several unami receptors have been discovered since around 2000. 1
It may even be proper to assign other sensations as distinct tastes as well. For instance fatty may be a taste, and I’ll bet you’ve thought, from time to time, that something tasted metallic. Put a penny in your mouth and tell me if that coppery taste is bitter or sour. No, it’s metallic.
Okay, so these things are all about taste. Sweet, sour, salty, bitter: these are all taste sensations. What we see here is that these individual tastes are about dissolved food compounds coming into contact with taste buds and this information being relayed to the brain. Plugging your nose will not cause your taste buds to not be able to detect sweetness, saltiness, or bitterness. An apple is much sweeter than a raw potato. In fact, a potato is not sweet at all. Regardless of whether your nose is plugged up, your taste buds will still transmit a “sweet” signal to the brain, which it will interpret as tasting sweet.
We could easily suggest some evolutionary reasons for why we are so tuned in to these four particular tastes, when we can smell so many different and distinct compounds:
- Sweetness: A sweet taste signals easy and ready fuel, in the form of simple sugars, that will provide a very quick source of energy to the body with little work.
- Saltiness: A salty taste signals the presence of Na+ and other salts, which we absolutely must have to stay alive.
- Bitterness: A bitter taste signals what could be a toxic substance, like one of many toxic alkaloids found in plants. Remember that a bitter taste is primarily one we avoid, but not completely. If you tasted an utterly bitter substance, you’d absolutely be averted from it.
- Sourness: A sour signals a high acid food and a high acid food, if we consumed too much, could alter our acid-base balance. Also, spoiled foods tend to be highly acidic. So a very sour taste is one we mostly avoid.
- Unami – The unami taste may signal the presence of protein. Think of a nicely grilled steak and how it makes your mouth water (my apologies to any vegetarians). 2
So, tastes either help us identify nutrient contents of food, such as sweet and salty, or help us avoid things that may be bad for us, such as sour and bitter. And even though we do seek out certain sour tastes, like citric acid and a bit of vinegar (acetic acid), and bitter taste like coffee; most of us have to acquire a taste for these things through repeated exposure, a little at a time. This also helps us learn to tolerate them.
Sucrose, or table sugar, tastes sweet. Obviously, this sweet flavor is always the same, correct?
Actually, our experience of the sweetness of sucrose can be influenced by our sense of smell. If you put sucrose into a mixture that gives off a fruity or floral odor, this mixture will be experienced as tasting more sweet than a mixture with the same level of sucrose that gives off a savory odor. We learn this through association.
Therefore, there is more to our perception of food than just the four “tastes.” Flavor is the total experience of all the taste sensations coming together to produce a unique experience for each food. This is much more complex than the simple act of detecting the individual tastes. People often say that losing your sense of smell causes you not be be able to taste, or to not to be able to taste as well. What they really mean is that your ability to experience flavor can be greatly diminished.
The key to understanding why people think plugging your nose blocks your sense of taste is in how the brain handles flavor as opposed to taste; as well as understanding that taste and flavor are two different things. So now it’s time for more science (neuroscience, isn’t this blog advanced?)
Smell, Taste, Flavor, and Your Brain
Compared to the sense of smell, the sense of taste is a minor and primitive thing. We do not have the olfactory sense of a bloodhound, which has about 200 million olfactory receptors while we have a paltry 20 million. But compare this to the sense of taste. We can detect four tastes, yet tens of thousands of smells. The one sense that has more receptors dedicated to it is vision.
We don’t have to get into how the olfactory receptors in the nostrils work. We just need to look at how the brain handles the signals. It’s a short path. From the olfactory sensors in the nostrils, information is sent to the primary olfactory cortex in a part of the brain called the piriform complex. This is connected to limbic system, where the parts of the brain responsible for emotions are found. This explains why smells can trigger such strong emotions in us. The amygdala and the hippocampus, two limbic structures, communicate with the olfactory system. In fact, only three synapses separate the amygdala from the olfactory bulb and the amygdala is critical in experiencing emotion. Only three synapes away as well, is the hippocampus, which is involved in associative learning and other memory things. You get the associative learning thing, right? You know how we tend to associate smells with memories of past experiences? Yep. This is why smell, memory, and the emotions connected with that memory are so intertwined. The connections between the olfactory area and the amygdala and hippocampus are more direct than to any other sense.
Olfactory information goes from the limbic system to the orbitofrontal cortex, which also receives taste information. It is here that the brain interprets flavor. The interpretation of flavor is a combination of the basic sensations of taste plus the sense of smell. All this information is put together to form your flavor sensation. If you lose your sense of smell, your ability to perceive flavor can be severely compromised. Food can still have basic tastesassociated with it, but there won’t be any overriding sense of flavor. Food will taste bland, or you will experience it in a completely different way. It is hard to predict how the loss of smell will affect each person, because, as you can see, the way flavor is processed is highly complex, depending on many, many factors coming together in the brain.
Now that you understand the difference between taste and flavor perception, you understand why many of us, if not most of us, will be able to tell an apple from a potato with our nose plugged and our eyes blindfolded. The apple may not have the exact flavor it would have had, and the potato may be different as well, but an apple is sweet and a potato is not and there is no reason why the brain will not receive this sweet signal from the taste buds and give you the sensation of sweetness, regardless of whether your nose is plugged. A Sour Granny Smith apple? Same difference. You’ll probably taste sour. And don’t forget the feel of the food in your mouth. Mouthfeel also influences our perception of flavor.
All in all, the oft-repeated experiment involving nose plugs, blindfolds, apples and potatoes; and the oft-repeated prediction that nobody will be able to tell the difference, is a myth. To understand what it’s like to have flavor perception changed by losing your sense of smell, it’s probably best to ask a person who has lost theirs. I’ve actually known three people who had no sense of smell. Which is weird. What is even more strange is I met them all in the same place where I worked! Anyway, all of them could taste but they’re preferences for food changed drastically, causing them to hate certain things they used to love, and vice versa. In fact, one person was really big into apples. Other fruit as well, but mostly apples. As for myself, an apple tastes the same to me whether my nose is plugged or not.
In my research for this post, I have been amazed at some of the things that authors have stated as absolute fact which really should have been a “speak for yourself” kind of thing. One such author, Jean Anthelme Brillat-Savarin in his The Physiology of Taste: Or, Meditations on Transcendental Gastronomysaid three things about the influence of smell on taste, one of which is the nose plug thing. 3 These things he wrote as if they are and absolutely indisputable scientific fact, true for one and all. I will paraphrase but I’ll leave the more interesting words intact.
- When the nasal membrane is irritated by a violent coryza (head cold) the sense of taste is completely wiped out.
Now that is a bold statement, but perhaps we should take a clue from the fact that he used the word coryza for cold. First, we have the amazingly inexact concept of the nasal membrane being “irritated.” Obviously, there are degrees of irritation. Here, I take it that the irritation is so profound that the olfactory receptors in your nose are not only irritated, but are so pissed off they’ve beaten your taste buds to death. This is, of course, the oft repeated statement “I can’t taste anything when I have a cold.” Well, I’ve personally had many, many head colds and not once, even during the most severe, did I find my sense of taste “completely wiped out.” Speak for yourself.
- If one eats with his nose pinched shut, he is astonished to find his sense of taste imperfect and faint; by this means, the nastiest dosage can be swallowed easily.
Again, overstatement. If one pinches shut his nose, one being me, one does not find his sense of taste faint at all. One can taste quite fine, thank you. And one does not wish to “swallow the nastiest dosage” in order to convince oneself of this fact. Again, speak for yourself.
- If one (again with the one) continues to leave his tongue pressed against the roof of his mouth at the moment of swallowing instead of letting it return to its natural place, the same effect will be produced because air will not circulate and the the sense of taste is “not aroused” and the act of tasting has not taken place.
I placed the quotations and bolding myself to highlight the funny parts. So this goes to show that the sense of smell and taste, together, comprise something that makes people believe weird things. But this one is so very ridiculous, that coupled with the fancy “ones” and other such language, it is a wonder a publisher was ever found. If you try to leave your tongue on the roof of your mouth while swallowing, what will happen is that you will find it very difficult to swallow, if you don’t outright choke on your food! The act of tasting will not be shut down at all; the act of swallowing will. You start tasting as soon as the first bit of food becomes dissolved and the solution reaches a taste bud or two. In fact, in the case of salt, the “act” of tasting takes place almost immediately.
Now, what is really outrageous is that this book has the gall to have the words “Physiology of Taste” in its title. Since that is followed by the quite meaningless, “Meditations on Transcendental Gastronomy,” one can see what one has got in store for one.
The moral, if there is one, is that if there is a wickedly ridiculous thing to be said about the influence of smell on taste, someone has probably wrote it in a book and printed it in mass. However, before we get too down on the author, I’ll admit that the book was originally written in the late 1800’s, when people, for one, used one too much, and for two, didn’t know as much as we do today about how taste and smell works (not that we know a whole lot.) Also, it was translated from French so some of the over-the-top language was probably the choice of the translator, republished in 1949. I sure hope nobody translates anything I write into another language and makes me sound like a complete and utter boor! I can do that for myself, thank you.
I fooled you a bit by not letting you in on the fact that the book was so old. But there is a point. The point is that a lot of what people commonly say about smell and taste may be held over from stuff like this written in books long ago. It happens all the time.
Losing the Sense of Smell
While it does seem strange to me to have known three people working in the same place who had lost their sense of smell, it apparently is not that unusual, affecting perhaps one out of a hundred, if not more (remember what I said about numbers, above). You can lose your sense of smell, which is called anosmia, through injury or illness. A blow to the head, as in sports, is a likely culprit. Such a blow might knock the cribiform plate out of its normal alignment. As this plate moves, it can shear off the olfactory axons that pass through it. This would result in permanent loss of smell. Upper respiratory viral infections or nasal polyps are other causes, but in these cases, smell might be regained. Nasal polyps, for instance, can be removed through surgery. I knew someone who lost their smell when they were electrocuted.
It is also possible to be unable to smell only certain compounds, but be otherwise able to smell normally. The compounds involved are usually steroidal musks like androstenone, and this is a genetic condition. (Additional sources: 4 5 6)
- Lindemann, Bernd, et al. “The Discovery of Umami.” Oxford Journals: Chemical Senses 27.9 (2002): 843-44. Web. 4 Oct. 2012.
- Chaudhari, N., and S. D. Roper. “Review Series: The Cell Biology of Taste.” The Journal of Cell Biology 190.3 (2010): 285-96.
- Brillat-Savarin, and M. F. K. Fisher. The Physiology of Taste: Or, Meditations on Transcendental Gastronomy. New York: Heritage, 1949.
- Brown, Amy C. Understanding Food: Principles and Preparation. Belmont, CA: Wadsworth Pub, 2011. 3-4.
- Longstaff, Alan. Instant Notes in Neuroscience. London: Bios Scientific, 2005. 211-214.
- Drobnick, Jim. The Smell Culture Reader. Oxford: Berg, 2006.