THE TRIGEMINAL NERVE

With all this discussion of receptors, you may be wondering where they are located in the mouth, throat, and nose, and what nerves they use for sending their messages.

The major nerve in question is the trigeminal nerve, also known as cranial nerve V. It gets its name from the fact that it has three major branches, which go to the upper, middle, and lower part of the face respectively. The area each branch serves is shown in this drawing  from Gray's Amatomy (1918). Green represents the ophthalmic branch, red(ish) represents the maxillary branch, which serves the inner part of the nose and the roof of the mouth, and yellow shows the area served by the mandibular branch, which serves the lower mouth and tongue.

Branches of the trigeminal nerve spread out all over the surface of the inside of the mouth, with small extensions into the taste buds.  The inside of the nose is also lined with branches of this nerve.

This nerve has two general functions: it sends sensations of touch, position, and pain, as well as warm and cold, to the brain from the face, eyes, and the inside of the nose and mouth; and it controls the muscles we use to chew.

In the inside of both mouth and nose, the sensations this nerve sends to the brain take on an added dimension (in addition to touch and the rest), because receptors on the nerve's endings that are activated by warmth and cold can also be activated by chemicals in the air and in our food. As a result, the trigeminal nerve modulates the sensations we experience from foods and beverages, now amplifying, now muting flavors, depending on which receptors are activated.

The trigeminal nerve enters the central nervous in the brainstem where it makes contact with the nerve centers responsible for making us awake, alert, and aware, for feeling emotions, and for focusing on tasks that require thinking.  Comfort foods are comfort foods — and black tea can be included among comfort foods —  in part because they activate the warm and hot receptors on our trigeminal nerve, which then links the flavor to warm fuzzy feelings. At the same time, you get a little wake-up call of increased awareness.

You may have found that sipping on a cup of green tea leaves you focused and refreshed.  By activating the cool/cold receptors, green tea sends a wake-up-and-pay-attention message via the trigeminal nerve, while we equate feelings of coolness with refreshment, in other words renewal of alertness.

Any questions?

PALATE CLEANSERS

Was in need of a palate cleanser after some sausage and beans, so got to thinking about palate cleansers in general. By definition, a palate cleanser is a dish designed to refresh your palate between rich dishes.

Rich dishes are ones that contain large amounts of umami flavors in the form of meat, and beans as well, coupled with sauces rich in fat, umami, and burnt flavors. A more elegant example than my sausage and beans: roast beef with mushroom demi-glacé. A dish like that virtually cries out for a palate cleanser.

Rebecca Franklin, French Food Expert at aboutfood.com, has a page about traditional French palate cleansers. Chief among them is a sorbet. She lists Apple and Calvados Sorbet, Lemon Sorbet, Lime Sorbet, and Mint Sorbet as typical.

Why do these sorbets work as palate cleansers?

The characteristic receptors activated by a rich dish like the roast beef are all warm and hot: TRPM5 by the umami flavors, and TRPM3 and TRPV1 as well as TRPM5 by ingredients in the sauce—note that the fat receptor CD36 that I mentioned in a previous post (MONDAY, FEBRUARY 22, 2016) also "talks" to the warm receptor TRPM5. Net effect: a mouth that is flooded with warm and hot, which can feel rich and heavy.

When you activate cold receptors you turn off warm and hot receptors: that is exactly what these sorbets do. Not only are they physically cold, they contain ingredients that activate the cool and cold receptors, TRPM8 and TRPA1. Take a spoonful of sorbet, and you will cool down and feel clean and refreshed.

Curiously, these flavors are quick-on/quick-off on their receptors, by which I mean that their effect is immediate, and there is little to no after-taste, because they leave their receptors quickly. 

Another beneficial effect: activation of these cool/cold receptors sends a "wake-up" message to the brain, so you will feel more alert and less sluggish.

As you go beyond the sorbets in Rebecca Franklin's list of palate cleansers, you will find that most of the other foods and beverages mentioned act on the cool/cold receptors—the exception is black tea...though you could have it iced!

But I would prefer a green tea as a palate cleanser, especially cold with lemon myrtle—lemon myrtle gives a deliciously lemony flavor without sourness. Friends of Pairteas at The Tea Spot have a blend for cold tea, consisting of green tea, green rooibos, and lemon myrtle, called "Keep Fit Organic," that's a big hit in my region. 

As Rebecca Franklin points out: "When choosing a palate cleanser, look for something with a clean, bright flavor that leaves little or no aftertaste."  That's exactly what activation of the cool/cold receptors does!

Here's a summer melon and lavender sorbet, by Chef Jeff Fisher of Crust in Cleveland Ohio, courtesy of Wikipedia. I feel refreshed just looking at this image!

PALEO-PANCAKE: HOW YOU CAN MODULATE FLAVORS IN A SINGLE DISH!

The other day I created paleo-pancakes with egg and banana. For those of you who don't know what a paleo-pancake is, here is the recipe:

Take a ripe banana and an egg (one of each—you can increase the recipe proportionately) and mash together. Fry the mashed combo as you would a regular pancake, either in unsalted butter or a little vegetable oil, et voilá! A delicious "paleo" breakfast treat — though I doubt that my Paleolithic ancestors in Northern Europe ever experienced such a thing...

An (over)ripe banana, perfect for paleo-pancakes!

Here comes the trick:

Taste one of your pancakes (part of one, if you only made one) without salt: the banana flavor comes out and the egg is muted. Then sprinkle a little salt on the remainder, and taste again. The egginess comes to the fore loud and clear and the banana practically disappears!

What is happening?  

Ripening bananas develop a number of different weak acids, primarily malic acid, but also good amounts of citric acid, and lesser amounts of a number of other organic weak acids. In other words (unlike the case for most fruits) the level of titratable acid in bananas goes up the more ripe they are. As discussed in a previous post, these acids inhibit our ability to taste the savory umami quality of the egg, so the pancake tastes primarily banana-y. Further, bananas have a number of flavor compounds that activate the cool/cold receptors, so the flavor compounds in egg that activate warm/hot receptors are suppressed.

Cooked egg has a number of characteristic flavor compounds that activate the warm and hot receptors. These include sulfur compounds that bind to warm (TRPV3) receptors. These compounds also enhance the sensation of umami by activating a warm TRP channel type, TRPM5. This channel is used by Type II taste bud cells to send sweet and umami messages on. These sulfur compounds appear to enhance the umami message in particular.

Another set of compounds produced by the cooking process give eggs (and banana too) a caramel-like flavor to the mix. These compounds activate the hot receptors, TRPV1.

What salt does is shift the balance among receptor activations. It, too, activates TRPV1, the hot receptor, so now we have warm, hot, and umami receptors to dial up the egg flavor. The flavor compounds in banana can no longer overcome this increase in "egg" sensation.

BTW, you will find multiple versions of this recipe on line, with a variety of additives. You might be interested in trying some of them and seeing what happens to the banana and egg flavors. If you do, please let me know!

PAIRING DOESN'T HAVE TO BE ONE BEVERAGE TO ONE DISH...

What do I mean by this strange statement?

I mean that when you have a complex dish, such as the French toast that Friend of Pairteas Marzi Pecen (tea expert/perfumery expert/flavor expert) enjoyed recently, you can choose beverages that will bring out different flavors in turn, first one and then the next, in other words two (or more) beverages with one dish.

Here's the dish she had:

It's French toast filled with dulce de leche, topped with apples, and covered with caramel and cinnamon. Incredibly rich!

While the toast, dulce de leche, caramel, and the cinnamon activate the warm and hot receptors, the apple activates primarily the cool receptors.  What beverage would one choose to go with this dish?

Here's a basic principle:  a beverage pairs well with a dish when they both activate the same receptors. When they do, the flavors of both stand out.

And another basic principle: warm and hot receptors inhibit cool and cold receptors and vice versa.

So what should you choose when you have both warm/hot and cool/cold elements in a dish?

Marzi chose grapefruit juice and coffee to go with this dish, with water as a chaser:

Excellent choice! And here's why:

Good coffee has multiple compounds that have a caramel flavor and that activate the warm and hot receptors, particularly the latter—the same receptors that are activated by burnt toast. That's why Marzi found that the coffee brought out the toastiness of the dish, and why it went so well with the caramel flavors. However, with this combination she could hardly taste the apple.

So she took a forkful of the dish with grapefruit juice, and a completely different flavor profile appeared! The apple came to the fore, because grapefruit juice has multiple compounds that activate the cold receptors; and the bitterness of the juice was sufficient to mute the somewhat excessive sweetness of the dish.

Take some water, repeat the sequence, first with coffee and then with grapefruit... Marzi had a kaleidoscope of flavors, and thereby complete enjoyment of a complex dish!

We have the habit of pairing one single beverage with a given dish, no matter how complex that dish is and how many disparate receptors it may activate. I recommend thinking of a dish as opening up like a book, with a new chapter revealed with each bite, with each chapter having its own music, its own accompaniment.

Thanks so much, Marzi, for giving us this excellent pairing example!

Smell and memory: how the olfactory system links to memory centers.

Proust's Madeleine Moment gives us a vivid description of the link between odor, vision, and event memory and, most vividly, place memory. How and why are odor and memory so closely joined?

The how is relatively easy to understand. Between the neurons in the olfactory bulb in the nose and the memory centers in the brain is a mere three steps.

Odorants enter the nose, where they are captured by the endings of nerve cells (olfactory cells) located in the olfactory epithelium at the roof of the nose. These nerve endings pass through holes in the part of the skull called the cribriform plate to reach the olfactory bulb. These nerve endings are shown in yellow in the image from Wikipedia, above.

Once inside the olfactory bulb, these nerves meet up the next nerve cells in line to pass the message along. These next nerve cells compose the olfactory tract. The picture below, from Gray's Anatomy (1918) shows the base of the brain, with the olfactory bulb (the Q-tip shaped pair of structures in yellow at the top), and the olfactory tract leading directly into the brain substance.

Once the olfactory tract nerves plunge into the substance of the brain, they meet up with the first set of important cells for memory, located in the entorhinal cortex. Cells in this part of the brain are responsible for coordinating input from vision as well as smell. In addition, cells in this part of the brain keep track of our movements and turns via input from the the vestibular system in our inner ear.  In this way they help make navigation and place memory possible.

This combined representation is sent, second by second, to the hippocampus, which records our experiences of action, event and place in memory; and to the amygdala, which gives memories their emotional color; and finally to the orbitofrontal cortex, right above the eyes, to evaluate our overall situation, compare it with our emotions and memories, and decide what to do. 

Why all this coordination focused on smell, vision, and motion? For a very practical reason: we have to remember where we went to get food and water so we can go back for more, and we have to remember where and when we met up with either danger or comfort, in other words where our friends and enemies (human, plant, and animal) were, so we can find them back or avoid them.

An aside that demonstrates the power of the odor-emotion connection, so richly described by Proust: a very recent study showed that if you present people with a pleasant odor followed by a picture of a face with a neutral expression (no emotion), people will consider that person to be pleasant and friendly. Conversely, if you precede the same face with an unpleasant odor, the person will be judged unfriendly and unpleasant!* 

Makes one wonder about the subliminal influence of odors in everyday life — if you meet someone over a deliciously aromatic cup of tea, would you automatically find the person to be so very nice?

* Stephanie Cook, Nicholas Fallon, Hazel Wright, Anna Thomas, Timo Giesbrecht, Matt Field, and  Andrej Stancak. Pleasant and Unpleasant Odors Influence Hedonic Evaluations of Human Faces: An Event-Related Potential Study. Front Hum Neurosci. 2015; 9: 661. Published online 2015 Dec 1. doi:  10.3389/fnhum.2015.0066

AN INTERLUDE...

After all the science in this blog I thought I would offer you an interlude—a paean to the tastes of tea and memory—courtesy of Marcel Proust (translation mine). Will be back to science in the next post, as I explain why Proust had this experience.

The Madeleine Moment

From Du côté de chez Swann by Marcel Proust

…and shortly thereafter, mechanically, loaded down by the dreary day and the prospect of a sad tomorrow, I brought to my lips a spoonful of tea into which I had let a piece of madeleine soften.  But at the very instant that the mouthful mixed with cake crumbs touched my palate, I shuddered, attentive to the extraordinary thing that was happening in me.  A delicious pleasure had invaded me, isolated, without notion of its cause.  It immediately rendered all the vicissitudes of life unimportant, its disasters harmless, its brevity illusory…I stopped feeling mediocre, contingent, mortal.  Where could this powerful joy have come from?  I felt that it was linked to the taste of the tea and the cake, but that it also infinitely outstripped the taste, was not of the same nature.

…I put down my cup and turned to my mind.  It was up to my mind to find the truth.  But how?  Grave uncertainty.  Every time the mind feels itself outstripped by its own self; when he, the searcher, is at the same time the cryptic country which he must search…Search?  Not only search: create.  He is facing something that isn’t yet, that only he can make real and bring to light.

…Of course, what vibrates like this deep inside me must be the image, the visual memory, which, linked to the flavor, tries to follow the flavor to me. 
…And suddenly the memory appeared to me.  The taste was of the little madeleine that…my aunt Leonie offered me after dunking it into her tea.

...But, when nothing remains of a remote past, after the death of beings, after the destruction of things, only smell and flavor, more frail but more lively, more immaterial, more persistent, more faithful, only they last for long, like ghosts, to be recalled, waiting, hoping (on the ruins of all the rest)  to carry, unbowed, on their almost impalpable droplet, the immense edifice of memory.

…and right away the old gray house on the street where she had her room, came to my mind like a stage set, attaching itself to the little pavilion …and with the house came the town, the Square where they sent me before lunch, the streets where I ran errands from morning to night and in all weather, and the paths one took when the weather was good…all the flowers of our garden and those on the grounds belonging to Mr. Swann, and the waterlilies of the Vivonne, and the good folk of the village and their small homes and the church and all Combray and its environs, all that which could take form and solidity, emerged, town and gardens together, from my cup of tea.

BITTER & BURN: A DOUBLE WARNING SYSTEM?

I was just going over a list of compounds that activate bitter receptors, and noticed that many of these compounds also activate the “hot” receptor TRPV1 and/or the “cold” receptor TRPA1, both of which cause pain when activated. These include compounds that activate the bitter receptor TAS2R38: ethanol, which burns by activating TRPV1; mustard and wasabi, which activate TRPA1, but also TRPV1 to some extent; and limonene in citrus fruits—especially their rind which we use for zest—which activates TRPA1. Limonene is what gives the zesty "bite."

Zesting an orange. Image from Wikipedia.

The structure of TAS2R38 differs considerably from person to person. Some people carry a version that functions well while others carry a version that doesn't function at all. The compound propylthiouracil (PROP) has been used to define who is and who isn't a "supertaster" based on whether a person carries a functioning TAS2R38 or not.

My thought is that even when a person fails to sense the bitterness of a compound, pain from activation of TRPV1 or TRPA1 may stop further consumption.

We think that the capacity to sense bitter tastes developed in order to warn us of potentially poisonous compounds in our foods. Perhaps the simultaneous activation of the bitter and the pain receptors is nature’s double fail-safe warning system.

ADD FAT to the LIST of BASIC TASTES!

Chances are you haven't heard of this, even though the data have been accumulating since 2005...fat isn’t just texture, though of course texture is part of the experience of fat in the mouth. Data from both humans and experimental animals suggest that we are able to taste fat, or, to be more exact, we can taste long chain fatty acids.

In a series of elegant experiments, Fabienne Laugerette and her colleagues demonstrated that rats and mice sense fat through a receptor protein on the tongue called CD36.* As it turns out, humans taste fat in the same way.** 

In other parts of the body this same protein carries fatty acids into cells. On the tongue, however, CD36 appears to activate the same mechanisms as do the bitter, sweet and umami receptors, and it  sends messages to the same taste nerves in the tongue as do bitter, sweet, umami, and sour.

CD36 is associated with taste buds on the sides and back of the tongue, with a few on the tip of the tongue. It sits anchored to the surface of cells near the tip of taste buds. On the part of the protein outside the cell it has a cleft lined with amino acids that are hydrophobic. In other words, these amino acids don’t like to associate with water but do like to associate with lipid. This cleft can trap free long chain fatty acids, but not triglycerides. 

This image from the paper by Laugerette and her colleagues, shows a taste bud on the left, with a taste cell with CD36 attached. On the right is a model of the CD36 protein (the green ribbon) in the cell membrane, with fatty acids entering into the cleft. We don't know whether the fatty acid can trigger the cell to send a taste message by just sitting in the cleft or whether it needs to actually enter the cell. In any event we do know that in other locations CD36 is a fatty acid transporter that brings fatty acids into cells.

The fats we eat come in in the form of triglycerides—three fatty acids held together by a glycerol molecule. The fatty acids have to be detached from the glycerol for us to sense “fat.” The enzyme that does this breakdown is called lingual lipase—and (surprise!) where there is CD36 on a taste bud there is also lipase sitting on the surface of the tongue right next to it! 

It takes a little while for the lipase to break down the triglycerides, so fat has to be in the mouth for a longish time for you to taste it, while the sensation of sweet is sent to the nerves practically instantaneously. 

Think of eating something deliciously fatty such as hot fudge sauce. Do you savor it, moving it around your tongue to get maximum flavor? Now you know why you do this!

* Fabienne Laugerette et al. CD36 involvement in orosensory detection of dietary lipids, spontaneous fat preference, and digestive secretions. J Clin Invest. 2005;115(11):3177-3184. doi:10.1172/JCI25299.

** Pepino MY1, Love-Gregory L, Klein S, Abumrad NA. The fatty acid translocase gene CD36 and lingual lipase influence oral sensitivity to fat in obese subjects. J Lipid Res. 2012 Mar;53(3):561-6. doi: 10.1194/jlr.M021873. Epub 2011 Dec 31. Note that the authors of this paper looked at genetic variation in CD36. This variation leads to different thresholds for fat taste and intensity. In other words some people are much more sensitive to the taste of fat than others, on a genetic basis.

BITTERNESS & HOW WE PERCEIVE IT in WINE & TEA (& COFFEE)

One of the outstanding characteristics of both tea and wine is their bitterness, yet the compounds that confer bitterness to each of these beverages are quite different chemically.  In tea, caffeine and the catechins are major bitter compounds (example below: (+)-catechin), 

while in wine it’s primarily alcohol (ethanol).

How can such different chemicals yield pretty much the same sensation that we call bitter? and why do people differ so much in their perception and appreciation of bitterness? The answers to these two questions lie in the genes for bitter receptors.  

We humans have some 43 different functional genes for bitterness receptors in a family of genes called TAS2R.  Each of these genes codes for a specific protein. Bitter-sensing taste bud cells use to these proteins to catch bitter molecules as they pass by.  Once caught, the cell sends a non-specific message — “bitter” — to the brain.

As you can quickly see, this number of different proteins (and therefore different receptors) is far lower than the number of different chemicals we call bitter. In other words there is no receptor that responds to just one bitter compound. For example,  the receptor protein produced by gene TAS2R38 responds to ethanol, but also to phenylthiocarbamide (PTC), the compound that you may (or may not) have tasted on a piece of paper when you were in biology class.

At the same time, ethanol binds not just to TAS2R38, but also to other bitterness proteins, for example the one from a gene called TAS2R13. A different TAS2R gene — TAS2R7 — produces a protein that responds to caffeine, and at least four different proteins from four different TAS2R genes respond to epicatchins. None of these epicatechin-responsive proteins appears to be the same as the protein that responds to either caffeine or alcohol!

I used the word functional above because we have at least six TAS2R genes that don’t produce a receptor protein. We know that these were once functional genes because of their DNA sequence—mutations that accumulated during evolution have rendered them non-functional. 

Evolution has also affected the functional TAS2R genes in humans—in fact TAS2R genes are among the most variable that we have! Above I mentioned PTC. This is a chemical that some people taste as extremely bitter, while others can’t taste it all. The reason for the difference lies in variations in the TAS2R38 gene: some people produce a protein from this gene that can bind successfully to PTC while others produce a protein that cannot.

You may have noticed that ethanol binds to TAS2R38…and yes, you are right in thinking that if you have a non-functional version of the gene ethanol will taste less bitter.  But that’s not the whole story: there is at least one other protein that responds to ethanol with a bitter signal, from gene TAS2R13. This gene also has variations. Importantly, variations in TAS2R13 determine the overall bitterness of ethanol, and modulate the overall intensity of the experience of ethanol—both burn and bitterness. 

From this ethanol example, you can quickly guess that people differ in their experience of tea bitterness as well. As noted above, TAS2R7 dictates the extent of our ability to sense the bitterness of caffeine. There is a variant of this gene that leads to loss of function, that is, a protein that does not sense caffeine. An initial single short steeping time extracts caffeine from tea without extracting significant amounts of catechins. People who have the non-functional version of this gene won’t taste bitterness in tea that is steeped for a short time, and won’t taste much bitterness in coffee either.

That isn’t the whole story with respect to coffee, however, because there are at least four other genes, TAS2R3, TAS2R4, and TAS2R5, and possibly more, that influence its bitterness. Each of these genes has variants that lead to function or non-function. Importantly, these variants are inherited together in what is called a haploblock. In other words, if you have the non-functional variant of one, you will almost always have the non-functional variant of the others.

In my research with Tim Hanni MW, we found that people who tolerate high alcohol “big red” wines drink their coffee black, while people who prefer lower alcohol white wines and sweet wines prefer tea and put a lot of sugar in their coffee if they drink it at all — activation of sweet taste bud cells inhibit bitter taste bud cells. 

Bottom line: the intensity of bitterness you experience in tea, wine, and coffee, and therefore the need for sweet or salt to modulate the bitterness, may be very different from the bitterness your friends experience. Makes sense?

PS: if you want the references to this article, please contact me—the list is very long so I haven’t included it here.

PPS: couldn't resist including this image, from: Noever, R., J. Cronise, and R. A. Relwani. 1995. Using spider-web patterns to determine toxicity. NASA Tech Briefs 19(4):82. Also: New Scientist magazine, 29 April 1995 and http://www.caffeineweb.com/?p=15.

MORE about HÄNIG's STUDIES & WHAT PARTICIPANTS SAID

In yesterday's post I talked about the misinterpretation of the tongue illustrations by David P. Hänig, that led to the development of the erroneous "tongue map." 

In his 1901 paper,* Hänig described a whole series of experiments he performed using his colleagues as participants with the goal of understanding the nature of taste and taste sensitivity.

Some of his other observations are quite remarkable. For example, he was the first to observe that we are far more sensitive to bitter than to the other tastes. Further, our sensitivity to salty is twice that to sweet, but an order of magnitude less than our sensitivity to sour, and three orders of magnitude less than our sensitivity to bitter.

One of Hänig's major concerns was to discover whether there are more than four basic tastes. He was particularly curious to know whether there metallic sensations could be a basic taste, and came to the conclusion that he could not tell. This is a matter of dispute to this day!

In the process of trying to find out the answer to the question of whether the taste of alkali could be one of the basic tastes, Hänig gave his participants tastes of a sodium hydroxide and a potassium hydroxide solution and asked them to describe what they experienced.  He gave quotes from them in his paper. 

Here's one of these quotes (translation mine):

"Salty is prominent, but there is something else with it. Salty, perhaps also sweet and savory with it. It can be a mixture of salty, savory, and sweet. Burning and pricking savory sweet."

He was this close to identifying what we now know as umami!!! 

Here's another quote: 

"Strongly salty, then after that bitter. Salty and bitter—pulling together. A very peculiar experience, I'll recognize it again anytime. One must have the experience, I can't describe it completely."

And the third:

"Primarily salty, perhaps also a bit sweetish and burning. After rinsing the mouth, definitely sweet. It isn't pure salt, ja, how can I express it."

Hänig was clearly frustrated by his participant's inability to describe experience. However, the concept of four basic tastes, derived from the ancient Greeks, dominated his thinking. He was puzzled, but concluded that the experience of these alkaline compounds represented the result of the nervous system combining the four basic tastes.

With this research, Hänig earned his PhD in Leipzig under the guidance of Wilhelm Wundt (1832–1920), considered by many the father of modern psychology. Wundt believed that you could study the human mind through introspection and evaluation of the conscious experience. Wundt had been a student of Hermann von Helmholtz (1821–1894), from whom he received a thorough background in experimenting with sensory perception from a physicist's point of view—Helmholtz had applied physics to the study of vision, hearing, and nerve conduction with some success. Wundt tried to carry out his experiments in this vein.

But taste and smell proved impervious to the Helmholtzian style of analysis. Furthermore, you tend to find what you look for. Wundt and Hänig came to their research with the concept of four basic tastes, and so Hänig's experiments involved primarily these basic tastes, with a side-excursion into the experience of alkali. No savory sensations to experience, except by chance.

It's worth noting here that another of Wundt's students, Edward Bradford Titchener (1867–1927), became a professor at Cornell University (where I worked for most of my career). He developed largest research program in psychology at the time, and mentored the the first woman graduate student in psychology in the US, Margaret Floy Washburn (look her up!). 

Margaret Floy Washburn. Image from Wikipedia.

At Cornell Titchener continued Wundt and Hänig's work on sensory perception. His widely used and influential college textbook "An Outline of Psychology" (1896) was instrumental in reinforcing the idea here in American that there were only four basic tastes, another one of these myths.

* You can see and download the paper here:  Hänig, David (1901). Zur Psychophysik des Geschmackssinnes. Philosophische Studien 17: 576–623.

THE TONGUE MAP...

As I mentioned in today's Facebook post (Facebook.com/pairteas), I was browsing through a book about tea that had emerged during my house cleaning. The authors presented a tongue map, stating that, because tastebuds can respond to different tastes, "you can create a tongue map."

The existence of a tongue map such as the one in the book I found is derived from a misinterpretation of the following figure:

This image was compiled from illustrations in a paper by David P. Hänig* about tongue perception and sensitivity to these four flavors.

Here's what Hänig did: with the participation of seven of his colleagues, he put tiny amounts of solution on eight different parts of the tongue and mouth to determine where each tastant could be experienced.  His colleagues tasted each of these solutions everywhere in the mouth except in the middle of the tongue and under the tip. Hänig even tried the uvula and tonsils, though didn't get data from some of his participants at these locations because they gagged! But those who didn't gag could taste the sweet, bitter, sour, and salty in those locations as well.

The drawings above correspond to the results Hänig obtained from five colleagues who gave the intensity of the sensations. The presence of dots indicates that the tasting was perceived in that location, while the closeness of the dots corresponds to the intensity of the sensations. For example sweet was most intense at the tip of the tongue, but could be tasted everywhere except in the middle of the tongue where there are few if any taste buds.

I think it is easy to misunderstand this diagram, given the artistic conventions of the turn of the Twentieth Century. Shading was represented by dots, so in a regular drawing of the tongue the edges  would have had more dots than the middle, to indicate the shape of the tongue. People probably interpreted the less closely spaced dots simply as shading and the dark areas where the dots blend into each other as the locations where each of the tastants could be perceived.

Hänig's paper is fascinating in more ways than this. In my next post, I will discuss how he anticipated  the interactions among salt, sweet, and savory discussed in yesterday's post.

* You can see and download the paper here:  Hänig, David (1901). Zur Psychophysik des Geschmackssinnes. Philosophische Studien 17: 576–623.

HOW DOES SOUR MAKE SWEET & SWEET MAKE SOUR?

In my previous post, about Tim Hanni's approach to make big red wines tolerable to those of us who are sensitive tasters, I promised to answer the question: how does sour make sweet and sweet make sour? It all depends on concentrations and the order of events.

But first, here's Tim's diagram again:

http://www.timhanni.com

In order to understand this cryptic answer, let's go back to a diagram I had on my Facebook.com/pairteas page:

The ovals in this diagram shows three different types of cells in taste buds. 

• Type III cells (yellow, on the right) have at least two functions: first, they send the final taste messages to the nerve that in turn send the message to the brain; second, they sense sour from aicids such as citric, acetic, and lactic acid (more about this function below)
• Type I cells (grey, on the left) respond to salt. When salt arrives on their surface, they stop bitter-sensing Type II cells from sending the "bitter" message to Type III cells. That's why Tim advocates a touch of salt to inhibit the bitterness of the tannins in wine. Inhibition of bitterness also inhibits astringency—will explain this point in a future post. Suffice it to say here that the perception of astringency requires activation of the bitter receptor.
• Bitter, sweet, and umami molecules bind to receptors on Type II cells (the three cells in the middle). Note that each individual cell responds to only one of these three kinds of tastants. 
• At high concentrations of sweet, activated Type II cells for sweet can turn off Type II cells responsive to bitter.
• Type II cells that respond to bitter compounds inhibit the response of Type II cells that respond to sweet. That's why you can't taste sweet when you eat something bitter unless you add a enough sweetness to overcome the bitterness blockade. That's a lot of sweetness! Or...if you add salt! Now bitterness is inhibited, so any sweetness present in the food or beverage has a chance to come to the fore.
• Finally Type III cells (yellow, on the right) do at least two things, as mentioned before: they respond to signals from Type II cells, and pass the message (sweet, bitter, umami) on to the taste nerves. BUT when sour compounds such as acetic acid (wine/vinegar), lactic acid (wine) or citric acid (from citrus fruits like lemon) are present, these cells inhibit Type II cells from sending messages of bitter, sweet, and umami. 

The key words in the previous bullet point is "when sour compounds are present." As I noted in a previous post (WEDNESDAY, FEBRUARY 17, 2016), the sour receptor is an "off" receptor. In other words you taste sour after the cell no longer brings the acid into itself because the concentration of acid outside the cell has dropped. However, the important point is that messages from the bitter, sweet and umami Type II cells are inhibited the moment acid enters Type III cells. Once the sour is diluted by saliva, the sweet and umami have a chance to come through, and there is even a rebound increase in sweet. Note that salt will inhibit bitter independently of sour, as does sweet, though more sweet than salt is needed to be effective.

That's why, by having a bite of something that is salty and mildly acid, such as a piece of steak with a good dollop of Béarnaise sauce—or something more intensely sour, such as a lemon (which induces massive salivation) along with some salt—before you take a sip of the wine, the wine will be diluted, sourness will be gone, and your taste buds will be ready to appreciate the sweetness and fruitiness in the wine, characteristics that had been hidden by the wine's tannins and acid.

Image from Wikipedia: 

Strip steak with tatin of shallots and bearnaise sauce.

Restaurant "les Ministères", 30 rue du Bac, Paris 7th arrond.

Notice the salt on top of the steak! Just imagine the wine...or the tea!

Conversely, if you start with something sweet, such as a highly sugared dessert, or a high umami food such as a piece of steak plain with no sauce or salt, and then drink the wine, the acidity of the wine will immediately turn off your ability to sense the food's sweetness and umami. The result is that the wine will taste extra dry, and as you salivate the wine will taste extra sour and bitterness and astringency will come through.

HOW SOUR and SALT WORK with WINE, PART ONE

On the previous blog post, I mentioned Tim Hanni MW (that stands for Master of Wine). Tim was  the person who got me thinking seriously about pairing issues.

Tim maintains that we should always drink wines that we like. For many people, this means embracing sweet wines and avoiding the bold reds that are supposed to be the pinnacle of a palate's sophistication.

In fact, as Tim points out, the more sensitive a taster you are, the less likely you are to tolerate bold reds. The alcohol burns more painfully, and the sourness, bitterness, and astringency of these wines are too strong for comfort.

Here is Tim showing us what to do if we are stuck with a bold unbearable red: use lemon and salt.

I've seen Tim blow the minds of people who hate the bold reds (but are scared to admit it), by having them taste the wine before and after sucking on a lemon with a little salt. The wine, which was so impossible to drink before, is now sweeter and less bitter, and its fruitiness is enjoyable.

(By the way, no power on earth, not even Tim with his lemon and salt, can make me like big California Cabernet Sauvignons—they have a chemical in them, 2-isobutyl-3-methoxypyrazine, the major flavor compound in green peppers, which I can't stand. Some Chinese pan-fired green teas I've tasted seem to have this chemical as well, so I can barely drink them. But back to the story...)

Here's a diagram from Tim's book, "Why You Like the Wines You Like: Changing the Way the World Thinks about Wine" (you can find out more about the book at http://www.timhanni.com):

This is the most general pairing diagram for wines, according to Tim, and it works!

What this diagram says is: go ahead and have the big red wine with your umami-rich steak, but only if you like your wine to taste bitter, astringent, and (this is my addition) with a strong burn from alcohol.

If that's not your idea of pleasure, but you must have the big red to show your sophistication, or just to make your host or guests happy, then salt your steak and enjoy it with a good Béarnaise sauce—this sauce is made with vinegar, which provides sourness, and with fat, which turns off the burn of the alcohol hitting your "hot" TRPV1 receptors. Yum!

In my next post I'll explain how to understand the paradox of using sour to make sweet and sweet to make sour. Stay tuned!

WHAT IS SOUR ALL ABOUT?

The following is an expansion of what I wrote on my Facebook page (Facebook.com/pairteas) on February 8, with additional new information, and some editing.

Have been interested in sourness, in part because I have an addiction for these:

Am fascinated by the succession of flavors that these sour-sweet gummies give — and as we shall see, the idea of a succession of flavors is critical to understanding what sour is all about. 

What is an acid?
Acid is a general term for compounds to which hydrogen ions can attach and detach. If the hydrogen ions are detached when the compound is in solution, the compound is called a strong acid—hydrochloric acid, for example. If only some of the hydrogen ions are detached, the compound is called a weak acid. Examples: acetic acid in vinegar, lactic acid in sour milk, and citric acid in lemon.

What are pH and titratable acid?
You may have heard the terms pH and titratable acid, particularly in connection with wines. 

• pH refers to the concentration of free unattached hydrogen ions in a solution —the lower the pH the higher the free hydrogen in concentration. 
• Titratable acid refers to the concentration of hydrogen ions that would be present in a solution if you were to separate them from the acidic molecule to which they are loosely bound. The process of measuring this concentration is called titration. Titratable acid concentration includes the concentration of both strong and weak acids in a solution. 

The tongue recognizes titratable acid as sour at fairly low concentrations. Surprisingly, you need much higher concentrations of a strong acid like hydrochloric acid, in which all the hydrogen ions are free (hence very low pH), to sense its sourness.

How do we sense hydrogen ions in the mouth?
We sense hydrogen ions through three different mechanisms. In the first two, the acid has to enter the cell with its hydrogen ion attached in order to elicit sourness. The third, a much less sensitive mechanism, senses free hydrogen ions.

The first mechanism involves cells in taste buds called Type III cells. Taste buds with these cells are abundant in the front and sides of the tongue, and are designed to sense sourness in foods and beverages as they come into the mouth.

The second mechanism involves a special receptor, TRPA1, on the nerve endings of the trigeminal nerve. This nerve has branches in taste buds, as well as throughout the mouth, nose, and throat. TRPA1 is a receptor for cold as well as for a number of different food compounds. Activation of this receptor causes us to feel pain as well as cold.

The third mechanism involves the hot receptor on trigeminal nerve endings, TRPV1. This receptor responds to free hydrogen ions on the outside of the nerve endings, giving a hot painful sensation. This receptor is abundant in the back of the mouth and throat.

How do the first two mechanisms, activated by weak acids, work?

To experience what the first two mechanisms do in response to a weak acid such as acetic acid, take a tiny spoonful of vinegar and dip the tip of your tongue into it. Don't put the vinegar into your mouth—you just want to get the sensation from your taste buds on the tip of your tongue. Your first sensation will be a sharp pain—that's activation of TRPA1—followed quickly by salivation and a sense of sourness, followed by...sweet (more about sweet in a second).

Vinegars at the supermarket. Image from Wikipedia

What is happening on your tongue?

First, TRPA1 on the trigeminal nerve ending cells take up the acetic acid with its hydrogen attached. In the cell the hydrogen ions separate from the acid, which drops the pH inside the cell, making the inside more acid, but in a controllable way. Then the nerve cell sends the pain message to the brain, and a message to salivate to the brainstem. Salivation dilutes the acetic acid so there is less acid for TRPA1 to sense, and the pain ceases.

=>> Note that it is important for the cell to control free hydrogen ions inside it because otherwise its metabolic processes would go awry. That's why the cell doesn't let free hydrogen ions in, just acids with their hydrogen ions attached—it can control exactly how many hydrogen ions are free inside it.

Acetic acid enters the Type III taste bud cell with its hydrogen ion attached as well. But here is a difference: the Type III cells respond to acid when the pH in the cell starts to go up again. In other words, it responds by sending the "sour" message when the acetic acid is diluted by saliva so that the amount of acid entering the cell drops! This is why the sense of sourness comes after the sense of pain when you dip the tip of your tongue into the vinegar.

While the message for sour is in force, Type III cells inhibit the taste bud cells for sweet, bitter and umami, but once the sour message ends, the other taste bud cells are released, and you get a rebound sense of sweetness. 

That's why I think sweet-sour foods are such a delight—you see-saw between the two tastes over time as you have the food in your mouth, and if TRPA1 is activated (for example with sauerkraut, which is acidic enough) you get a burst of coolness as well as slight pain, which dissipates only to return with the next bite.

What about the third response, with the hot receptor TRPV1?

If there are too many free hydrogen ions for your saliva to neutralize, then TRPV1 (hot) receptors in the back of the tongue and in the throat take over. These receptors sense free hydrogen ions directly. Furthermore, it is made more sensitive to these hydrogen ions by activation of TRPA1. TRPV1 sends its "burn" message, with the goal of making you stop drinking or eating, and making you want to grab some water to dilute the acid. 

What does this mean for tea?

When you add lemon to tea at low concentrations, citric acid doesn't activate the trigeminal nerve endings but it does enter the Type III cells in the taste buds. These cells send the "sour" message while turning off the "bitter" message. As you finish your sip, the tea may taste sweet. That's what you may need to decrease the bitterness of a bagged tea.
.
If you put in too much lemon, you get a double whammy of painful sour, first from the cold receptor TRPA1 which responds to the citric acid, and then from TRPV1—lemon juice also has a lot of free hydrogen ions. If these hydrogen ions are not neutralized by saliva and tea, they hit the TRPV1 receptors in the back of the mouth and in the throat. The result is not pretty.
=>> In other words a little lemon is nice, but too much...Oh my!!!

And for those of you into wine...

I started this post by discussing titratable acid, one of the measures performed on wine for purposes of determining (among other things) the degree of fermentation. In my next post, I'll talk about how my friend Tim Hanni's system for pairing food and wine works by changing the balance among acid, salt, and ethanol. Stay tuned!

Friend of Pairteas and Master of Wine Tim Hanni