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Taste & Texture, Part One


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#1 eGCI Team

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Posted 23 April 2004 - 05:41 AM

TASTE AND TEXTURE

PART I: TASTE


SOME DEFINITIONS AND TECHNICAL TERMS

In line with most of the writing on the topic, I'll use "taste" to refer specifically to what we perceive through the taste buds and "flavor" to mean the perception that results from the combination of our senses of taste and smell.

Technically, the sense of taste is called the gustatory sense; the sense of smell is called the olfactory sense.

Both the sense of taste and the sense of smell are often called the chemical senses, since they transmit information generated by chemicals to nerve cells, resulting in neural impulses.

Chemosensory irritation is the term used to refer to the burn of mustard or the capsaicin in chiles, the tingle of carbonated beverages or the cool afterglow of menthol. These and other sensations (other than tastes and smells) are also called cutaneous sensations as they are perceived on the surface of the mouth ("cutaneous" = "of the skin").

TASTE, SMELL AND FLAVOR

Being the annoying, teacher's-pet, know-it-all child that I was, I loved amassing facts so I could spout off and prove how smart I was. I especially loved facts about biology and physiology; my older sister and her best friend actually gagged me and tied me to a tree in the backyard when I wouldn't shut up about the humidity of the air in our lungs. Looking back on it, I can't say that I blame them.

But my point in bringing this up is this: for a long time, I thought I knew a lot about a lot of things, the sense of taste included. I knew, for instance, that the bumps on the tongue were taste buds and were the site of our sense of taste, that there were four basic tastes and that we tasted the four tastes on different parts of the tongue. I also knew that an onion would taste like an apple if you plugged your nose, which was a riddle from sixth grade science class that, for some reason, I still remember to this day.

Unfortunately, it turns out that just about everything I thought I knew about taste was wrong, or at least incomplete. Now, taste researchers are learning an amazing amount about how our sense of taste works, and one by one, I'm correcting my earlier mistakes.

Those bumps you see on your tongue, called papillae, are not taste buds. But they contain taste buds (or at least some of them do), which in turn contain the taste cells, which is where the real action happens. Like any other sensory function, taste is, at the neural level, all about electrical charges. The molecules in your food that are responsible for the basic tastes change the electrical charge in the taste cells, which causes them to fire and convey information about taste to your brain.

Scientists agree that the number of different tastes we can perceive is very limited, but they don't all agree on exactly how many basic tastes there are. Sweet, sour, salty and bitter are universally accepted as true tastes; some researchers posit a fifth taste called "umami," a Japanese term that's usually translated as "savory." Some would also argue that "metallic" and "alkaline" (or soapy) count as basic tastes; however, since ideally those two tastes do not occur in our foods, I'm going to ignore them here.

The chemicals in salts and acids that account for their characteristic tastes act directly on the ion channels in the taste cells. Those in sweet and bitter substances are less direct; they bind to surface receptors that are coupled to certain proteins (called "G-proteins" for reasons we need not get into), which begins a series of reactions that ends in the change in electrical charge. Glutamate, the molecule which is now thought to stimulate the umami taste, also binds to receptors, but much less is known about what happens between the binding of the glutamate molecules and the change in polarization.

Because there are a number of reactions involved in our perception of sweet and bitter tastes, it's not surprising that scientists tend to concentrate on these tastes. The more steps involved, after all, the more opportunity for experimenting with the process. For example, by altering one of the G-proteins in mice, researchers actually changed their taste preferences. The altered mice no longer sought out sugar water and avoided bitter compounds, as normal mice would, but instead drank bitter solutions as readily as they did plain water.

But it's not just rodents' taste buds that are the subject of study. It's long been recognized that a chemical in artichokes, cynarin, makes other foods taste temporarily sweeter to most people. More recently, researchers have been working with chemicals that can block our ability to taste sweet or bitter flavors (it's thought that adding these "bitter blockers" to medicines might make them easier to take). Some preliminary research with humans seems to indicate that capsaicin, the chemical that puts the "heat" in chile peppers, temporarily lessens our sensitivity to bitter and sweet flavors but leaves our perception of acids and salts unaffected.

To react with the taste cells, any taste molecule, or "tastant," must be dissolved, which is the reason saliva was invented. That's why, when you swallow a pill – however bitter – you won't taste it if you get it down before it starts to dissolve. It's also why so many nasty tasting pills are encased in a coating that's hard to dissolve. Some tastants dissolve best in water; others are fat-soluble. Still others dissolve in alcohol, which incidentally also dissolves the water- and fat-soluble molecules as well. This is part of the reason why a little alcohol in a dish can make such a big difference to its taste.

What is still commonly taught about localization of taste sensitivity on the tongue is based on the misinterpretation of some early data from taste research. Now it's known that although particular taste cells do seem to respond best to one type of stimuli (salt, sour, sweet or bitter), they are capable of responding to all of them in some degree, and all four (or five) tastes can be sensed on any area of the tongue that contains taste buds. So, that map of the tongue we all learned about – the one where we taste only sweet things on the tip, bitter at the back, sour on the sides and salt along the edges – is wrong. (But many people still believe it; be gentle when you break the news.)

The temperature of the food we're eating has a noticeable effect on how intensely we can taste it. Bitter substances taste less bitter hot than at room temperature, which explains why cooled coffee seems more bitter than the hot brew.

Sweetness, on the other hand, is much less perceptible at very low temperatures than at room temperature. If you've ever made ice cream or sorbet, you may have noticed that the frozen product seemed less sweet than the mixture did before freezing. Similarly, if you've ever drunk a lukewarm soda pop, you likely noticed how sweet it seems. Those drink manufacturers expect their products to be quaffed over ice or straight from the fridge, and they keep that in mind when formulating their recipes. Cocktails, too, are meant to be drunk ice cold; a lukewarm cocktail is a miserable thing indeed.

Sweetness may be the flavor most noticeably subdued by cold, but all flavors, even bitterness, decrease in intensity at very cold temperatures. Despite its popularity, ice-cold beer doesn't have very much flavor, which is why beer aficionados prefer their brew warmer than it's often served. Likewise, chilling a white wine can be easily overdone – most white wines are best cool but not icy. And that's why even foods that are supposed to be "cold," like salads, benefit from sitting at room temperature for a while; they have much more flavor than they do straight from the refrigerator.

Let's go back to neural pathways for one last point. Other neurons in the "taste pathway" respond to and convey information on the intensity of any given taste, the temperature of the food, "mouthfeel" and sometimes pain at the same time the taste cells convey their information about salty, sour, sweet and bitter. These other stimuli are also responsible for the fact that tastes seem to originate from the entire surface of the mouth, and not from just the papillae that contain the taste buds. Thus, while in theory we can talk about "pure" taste sensations, in practice it's much more difficult to isolate them. This is especially true for taste and our sense of smell.

THE OLFACTORY SENSE

Anyone who's ever had a bad head cold knows how much our olfactory sense contributes to what we think of as taste, as does anyone who's ever tried to enjoy dinner while seated near someone with overpowering perfume or cologne. When all you can smell is gardenia blossoms or Old Spice, it's hard to taste your potatoes or cauliflower.

While we can discern only a small handful of different tastes, our sense of smell is much more sensitive. The average person can identify thousands of different odors and discern about ten intensities of each of those. Roughly a thousand different types of olfactory receptors are located on a small patch in the upper part of the nasal cavity.

We sense smells when odor molecules reach the receptors and dissolve; because the receptors are located above the path that air follows when we breathe normally, we can smell odors better if we sniff, drawing the air up to the receptors. The odor molecules can reach the receptors either through the nose or up through the pharynx, the passage connecting the mouth with the nose, which is why one of the best ways to detect the aromas of our food is to exhale with the mouth closed as we're eating – it forces the air up through the pharynx.

The connection between the mouth and the nasal passage accounts for the fact that taste and smell combine so thoroughly to produce the phenomenon we think of as flavor. The passage of odor molecules through the pharynx also accounts for the fact that although holding or plugging your nose will greatly diminish the flavor of your food, it will not completely eradicate it (an onion will not taste like an apple). It takes pretty severe nasal congestion to do that.

All substances, including foods, release more odor molecules when warm or hot than when cold, so their smells are much stronger. That's the reason garbage is so much more revolting on a hot day and the reason warm or hot foods tend to smell so much stronger than cold foods.

NATURAL AND ARTIFICIAL FLAVORS

Maybe you've heard wine geeks talk about flavors of berries, oak, apples, melon, toast, pepper and even grass in various wines. Wait a minute, you say, wine is nothing but grapes and yeast, so how can it have all those other flavors? That's where the molecules come in. As wine ferments and ages, it goes through a lot of chemical changes, which result in all sorts of tastants and, especially, odor molecules being produced. Some of these molecules are very close to the odor molecules in other fruits or even vegetables, spices and grass, so they trigger the same receptor cells that the actual fruits, vegetables and spices do. We thus perceive the wine as smelling and tasting like all those other substances.

Some researchers spend their time delving into the molecular structure of the foods we eat in order to isolate the molecules responsible for various flavors (they have, in fact, isolated more than 4000 such flavor compounds). They can then concentrate them and add them to other foods as "natural flavors." But they can also go one step further and analyze the concentrate with a chromatograph to see how the molecules are actually put together. With such an analysis, researchers can then sometimes reproduce the compounds artificially and use them to create such monstrosities as buttered-popcorn-flavored jelly beans.

The problem with either natural or artificial flavors, the reason they never quite taste like the original, is that foods have numerous molecular compounds responsible for their characteristic flavors (fruits, for instance, can have hundreds of such compounds). Researchers necessarily focus on a few that seem to provide the most recognizable flavor and aroma, but they can't reproduce them all, so the resulting flavoring is fairly one-dimensional. Technology is improving in this area, though, so who knows? Maybe someday watermelon candy will actually taste like watermelon.

THRESHOLDS AND DESENSITIZATION

All of our senses react best to changes in stimuli. Studies with infants show that they quickly become bored watching the same scene; their interest increases whenever a new element comes into view and then fades if the object stays in view for long. Similarly, we can usually "tune out" a constant, unchanging noise without much effort, but our ears will still perk up at the sound of anything new and different.

It's the same with taste and smell. We get used to odors and flavors pretty quickly if they don't change much, and it takes stronger and stronger concentrations of the taste or odor molecules to elicit the same reactions. That's why some people wear so much perfume or cologne, especially if they've been wearing the same scent for a long time – they've adapted to the smell, so they keep dousing themselves with ever-increasing amounts to be able to detect it.

Likewise, someone who uses a lot of salt regularly will require more and more of it in order to notice it; that person's salt threshold has increased. It doesn't even take long-term exposure to a certain taste to become desensitized; depending on the taste, we can start to adapt quite quickly. As we'll see in the next section, it can happen with chemosensory irritants as well, such as the capsaicin in chile peppers.

TASTERS, NONTASTERS AND SUPERTASTERS

So far, I've been working on the basis that everyone's sense of taste and smell is exactly the same -- that we all taste the same things with the same intensity. But this is not true. Certain medical conditions can affect our gustatory and olfactory senses, and some physiological factors also affect our sense of taste.

If you're old enough, you might remember a day in science class when the teacher passed out little slips of paper and told you all to put them on your tongues. She then sat back and watched, probably with some amusement, while some of the class sucked on them for minutes with nothing but a puzzled expression and others immediately spat them out, violently and with looks of betrayal.

Those little slips of paper were coated with PROP (6-n-propylthiouracil), or PTC (phenylthiocarbamide), chemicals that taste extremely bitter to some people but are tasteless to others. It turns out there's a genetic component to how strongly we taste things. In technical terms, the ability to taste these chemicals is determined by whether one has a particular dominant gene: those with two recessive "taste" genes are known as "nontasters," those with one recessive and one dominant are "tasters" and those with two dominant genes are called "supertasters." Overall, about a quarter of the population are nontasters, one quarter supertasters, and the remaining half are tasters.

Supertasters have a significantly higher number of taste buds than tasters, and both groups outnumber nontasters for taste buds. The averages for the three groups are 96 taste buds per square centimeter for nontasters, 184 for tasters, and a whopping 425 for supertasters. Not surprisingly, then, supertasters tend to taste everything more strongly, not just those two chemicals from science class. Sweets are sweeter, bitter things more bitter, and salty things saltier. I've heard more than one supertaster report that pickled foods taste like ammonia. Supertasters are less likely to enjoy the taste of alcohol as well.

When I first started reading about this phenomenon, I thought, "I want to be a supertaster -- it sounds so refined, so superior." Alas, I concluded, I'm not. Then, as I continued to read up on the subject, I realized that it might not be so great to be a supertaster. Not only do many foods taste unpleasantly strong to them, but also (since our taste buds also convey information on temperature, pain and mouthfeel) the bite of chiles, mustard and ginger is unbearable and very hot or cold foods can be practically unpalatable. Foods with a high fat content seem unpleasantly greasy. Thus, supertasters tend to be very picky eaters. Nontasters will eat damn near anything, neither greatly liking nor disliking what they eat. Tasters, the least homogeneous group, vary a great deal in their likes and dislikes, but overall they tend to genuinely enjoy the widest variety of foods.

So, we've looked at the way we perceive the basic tastes on the cellular level. Now, on to a more general look.

THE BIG FOUR (OR IS IT FIVE?)

Sweet

We're born with an affinity for sweet tastes, one of the few instincts we have and apparently the only taste preference we have from birth. From an evolutionary standpoint, it makes perfect sense: sweet foods are energy-rich foods. Even though most of us in the developed world don't lack for calories, we still like sweet foods, at least to some degree. Many of us, however, lose some of our love of purely sweet foods as we grow older; we prefer our sweets tempered with a touch of acid or even bitterness.

As an element of flavor, sugar and other sweeteners often have the effect of softening or rounding out sharper flavors, which is why a sweet ingredient pairs so well with acidic or bitter ones. But eating sweets can temporarily skew your taste buds so that mildly acidic foods will taste very sour. That's why only the sweetest of wines can match well with desserts. And heavily sweet foods also have a tendency to deaden the palate somewhat, which is one reason that very sweet drinks and foods are usually served after meals.

Sugar also has an interesting effect on some other flavors, allowing us to perceive tastes we wouldn't otherwise. Researchers in England had their subjects chew mint-flavored gum, which was sweet, until the flavor had gone. The molecules responsible for the smell and thus the flavor of the mint were still present, but the volunteers could no longer perceive them. However, when they added a pinch more sugar to the gum, they once again smelled and tasted the mint.

Salty

As a rule, our love of sugar only barely edges out our fondness for salt. Most of us start to develop a liking for salty things between four and six months of age. Salt being an essential mineral for life, it's no wonder we seek it out. Add to that the fact that it's an excellent preservative for food, and it makes even more sense, from an evolutionary standpoint, that salty foods appeal to most of us.

If sugar rounds and softens flavors, salt heightens and perks them up, often without really making its presence explicitly known. If you've ever eaten pasta cooked in unsalted water or bread made without salt, you know what I mean here. They're incredibly bland, compared with the versions cooked with salt. But the pasta and bread cooked with salt don't taste salty, so much as they just taste like something. Any time I make a dish that seems one-dimensional, flat or boring, my first remedy is almost invariably to add a pinch more salt. It's not always the answer, but in most cases, it's a good guess.

Sour

It takes most children much longer to develop a fondness for sour foods than either sweet or salty foods. Some of us never really take to purely sour foods, although most of us grow to enjoy mildly acidic ingredients, since acids are as much of a flavor booster as salt can be.

But the tang of citrus or vinegar perks up flavors in a different way from salt. I describe the difference by saying that salt heightens flavor, while acid sharpens it. Acidic ingredients make us salivate, which, as we've seen, means that more tastants reach our taste buds. So while sour ingredients make their own presence known, they also make other flavors come forward. Sometimes when you're tasting a dish and it's a bit "flat," it's difficult to tell if it needs more salt or more acid. If you think you've added enough salt to a dish but it's still not quite right, try a squeeze of lemon or a splash of vinegar to see if that's what's missing.

While sugar and salt are nutrients we need for survival, acid does not appear to be. So why, then, can we distinguish sour as one of the basic tastes? The reason isn't entirely clear, but it may have been beneficial for our ancestors to be able to gauge the pH level of the water they drank. Or perhaps the ability to reject unripe fruits, which tend to be sour, made for fewer stomach aches and less gastrointestinal distress.

Just as important as their taste is the role that acids play in mouthfeel, and we'll investigate that aspect of them in the next section.

Bitter

The last of the "big four" tastes is bitter. Although we can detect bitter tastes early in our development, we don't tend to enjoy them; instead we do our best to avoid them. A liking for bitter tastes develops very late in life compared with the other three; indeed, some people never develop a taste for bitter foods at all (very generally speaking, Americans tend to shun bitter foods more than other cultures). That's probably the reason that the bitter foods we do eat are often looked upon as sophisticated and "grown-up." Coffee, dark chocolate, quinine (tonic) water, beer, bitter alcoholic aperitifs, bitter salad greens like arugula – we speak of them as "acquired tastes."

And it's no surprise that bitter foods are scorned by so many. In the wild, bitter things are usually trouble -- they make us sick or kill us. In terms of evolution, we probably developed the ability to detect bitterness so we could spit out the offending plants before we swallowed them. So why on earth do some people develop a liking for something so initially repelling? Part of the reason is that bitter foods, like spicy foods, make our taste buds stand up and take notice, so to speak. They provide novelty, which we've already seen is something we need if we want to avoid becoming desensitized. Think of bitterness (in small doses) as nature's palate cleanser.

UMAMI

Earlier, we took a quick look at what researchers have found about glutamate and how it results in the flavor known as "umami" (often described as "savory" or "broth-like"). We saw that they aren't agreed on whether it counts as a basic taste.

On the one hand, the Japanese have long regarded umami as a quality separate from the "big four" of sweet, salty, sour and bitter. And it's true that current research suggests that glutamate triggers taste cells in a completely different way from the tastants that trigger the other four tastes. Two researchers from the University of Miami have isolated a receptor that binds glutamate and proposed that it underlies the umami taste.

Empirically speaking, it's possible to measure the glutamate levels in foods and thus determine their umami level. Generally, protein-rich foods like cheese, meat, seafood and mushrooms contain significant amounts of glutamate. Aging, curing and fermenting enhance umami, as does ripeness (a ripe nectarine, for example, has more glutamate than an unripe one). Monosodium glutamate (MSG), which occurs naturally in many foods and is used as an additive in others, is the form of glutamate we're probably most familiar with.

But that's not the whole story. Part of the problem stems from the wide variety of foods that are high in glutamate. Although many of them can be accurately described as "savory," some of them, like grapefruit or green tea, don't seem to fall into that category as neatly. It's thus not always easy to recognize the umami "taste" in the same way we can recognize the other four tastes.

To complicate matters further, Japanese chefs (and now some Western chefs as well) seem to use the term umami metaphorically rather than literally. That is, chefs will speak of the umami of any food, meaning the best or perfect specimen of that particular food. They don't seem to be talking about glutamate levels; they almost seem to be speaking of what, given my philosophy background, I would call Platonic forms.

Whichever sense of the term umami people mean, though, it's clear that whatever it is, taste or sensation or Platonic form, it's not easy to talk about, at least not for non-Japanese. Even the experts have a hard time defining it. One sensory psychologist at Monell Chemical Senses Center in Philadelphia (the place for taste research) described it as "that meaty, mouth-filling, savory sensation" -- not what I'd call the most precise definition.

But even though the psychologist's response was not ideal, it says one thing loud and clear to me. She doesn't call umami a savory taste, she calls it a "sensation" -- more specifically, a "mouth-filling" sensation. I assume that most taste researchers are pretty precise when talking about this sort of thing, so when she said it was a sensation she no doubt meant it.

From my experience as well as my research, I think umami is not so much a taste as it is a cutaneous sensation. Or, more precisely, it seems to me that we experience glutamate simultaneously in two ways: as a unique combination of taste and sensation. And further, I think it's the sensation part, the textural element, that we experience most strongly, and thus I'll talk about umami again in the section on texture and mouthfeel.

There is one undeniable effect of umami on our sense of taste, however, so let me mention it before we go. Foods high in umami (glutamates) intensify many other flavors. They do this in ways we don't quite understand. One theory is that the presence of glutamates makes certain taste molecules adhere to our taste cells longer than they would otherwise, so their taste is more intense. Whatever the exact mechanism, though, the food industry has counted on the flavor boosting qualities of MSG and other glutamates for years. And so have countless cooks who use fermented foods, mushroom essence or aged cheeses to enhance their menus. Food scientists and chefs might not know precisely how it works, but they know it does.

THE FOUR TASTES IN COMBINATION

For the most part, the basic tastes don't occur in foods solo. We've seen that our sense of taste reacts best to changes in stimuli, so perhaps it's no surprise that we like foods that excite more than one type of taste reaction. Because sweetness, salt, acid and bitterness are the foundation of our entire experience of flavor, the balance among the basic tastes can make or break a dish, even if we don't consciously realize it. Experiencing and studying the ways these tastes combine and balance each other, then, is one of most basic and crucial steps in analyzing dishes and learning to cook.

Sweet and Sour

Lemonade, sweet and sour pork, the perfectly ripe orange: all of these share, to varying degrees, a balance of sweetness and acidity. Probably the first example of the sweet and sour combination that most of us taste and enjoy is the flavor of fresh fruit. We often talk as if ripe peaches, strawberries and pears are sweet, period, but actually their sweetness is balanced with a slightly tart element. Oranges and tangerines might display their acid more obviously, but virtually all ripe fruit has a sour edge that holds that sweetness in check.

It's a two-way street with sweet and sour ingredients. On the one hand, sweetness is full and round, but by itself, it can be cloying and overwhelming. Sour ingredients by themselves are sharp and "cutting." Add a bit of something sour to your sweet base, and you get the best of both worlds -- round, full flavor with a sharp edge that cuts through the cloying sweetness. Add more acid so that sour is your primary taste, and you still have the softening effect of the sweet ingredient to hold the tang in check. It's a match made in heaven.

Bittersweet

No, wait, the match made in heaven is the bittersweet one. Sweetness does have an affinity for both the sour and the bitter; it's a toss-up which is the more sublime combination.

We've seen that purely bitter foods are rarely eaten alone; most often the bitter is balanced by sweetness. Bitter aperitifs all contain a hefty dose of sugar or other sweetener, as does tonic water. The bitter edge to coffee is something many people prefer to soften with sugar.

But looked at from the other direction, the sweet is also balanced by the bitter. Like acid, a touch of bitterness can cut the cloying quality of purely sweet foods. That cola you're drinking? You might not notice it, but it's got a fairly strong bitter kick to it. Even the sweetest milk chocolate contains a bitter undertone, and few sweets are more popular than chocolate.

Sweet and Salty

Maybe this coupling is not as obvious as sweet and sour or bittersweet, but sweetness and salt do a lot for each other as well. A pinch of salt can add amazing depth to caramel or custard, even though you don't really taste anything salty. Likewise, a tiny bit of sugar in a savory dish can bring together the flavors in a way that salt alone cannot.

But the match-up between salt and sugar goes further than merely supporting the other's feature role. While French and Italian cuisines rarely use a noticeable sweet element in savory dishes, this combination is very common in Asian cuisines. British and American cooks make use of it as well, in such dishes as lamb with mint jelly or roasts served with Cumberland sauce. And think about the snacks we eat – salty popcorn and a soda. Honey roasted nuts. Salted nuts in caramel. We enjoy a lot of sweet and salty combinations.

Unlike bittersweet or sweet and sour combinations, though, sweet and salty elements seem to balance each other in a different sense. While bitter and sweet (or sour and sweet) combine so thoroughly as to almost be a single new taste, sweet and salty combinations don't really lose their duality. It's as if our taste buds keep themselves entertained by switching back and forth between the two tastes without ever really reconciling them.

Salty and Sour

Since salt and acid are both sharp, it's perhaps surprising that combining them would work. But, on reflection, of course it does. Almost everything pickled is packed in a combination of salt and vinegar, and even when salt is the sole ingredient added (as is the case with cabbage to make sauerkraut), acid is a byproduct of the fermentation process. But this combination is not universally liked. I mentioned earlier that supertasters often report that pickled foods taste like ammonia, and I know plenty of people who don't seem to like anything pickled. Me? I could eat a whole jar of pickles or olives standing in front of the refrigerator. (They have to be really good pickles, though.)

Many cookbooks will tell you that acid will help an oversalted soup or stew. Research, however, shows that the story is not that simple. The tests aren't very conclusive, but in small amounts, acid seems to enhance salty flavors; in larger amounts, some, not all, acids do seem to diminish the salty flavor. I find that the amount of acid necessary to counteract too much salt in, say, chicken broth, will make the broth overtly sour, which may not be an improvement.

Salty and Bitter

Now, this may not seem like a combination we'd ever strive for, but salt actually helps to cancel the bitterness of foods. A couple of years ago I heard Harold McGee, a food scientist and author, report on an experiment he participated in wherein the subjects added salt to tonic water. They used a salt other than sodium chloride, one that didn't taste "salty," so they didn't have that taste to contend with. McGee said that given enough salt, the tonic water eventually tasted just sweet, not bitter at all.

If you add table salt to tonic water, you can start to taste this effect, but it will begin to taste salty before it stops tasting bitter, which can be confusing. If you're interested in another way to test this phenomenon, though, try adding a little extra salt to a salad dressing for bitter greens and see if it doesn't help to temper the bitterness.

Sour and Bitter

Nope, not by themselves. I can't think of a single food or dish that combines only these two elements, or at least not one I'd want to eat. But with a sweet element, it can work. Think of cranberry juice -- not only are cranberries sour, they also have a bitter edge. Add sugar and the juice is surprisingly refreshing. Likewise with grapefruit juice; it may be mostly sweet and sour, but a little bitterness is there too.

Taste Triads

The sour-bitter-sweet combination is also common in cocktails. And, if you add a bit of salt, you have the basis for one of the classic cocktails: the margarita. A well made margarita is a good mix (some might say the perfect combination) of all four elements: you have sweetness from the triple sec, sourness from the lime juice, which also has a definite bitter side, and the salt on the rim.

I'm getting ahead of myself here. However, it does lead me to the next level -- that is, combining more than two of the basic tastes. As I've just mentioned, we do it occasionally, although we might not realize it. A chocolate lover who eats orange filled truffles is combining sweet, sour and bitter flavors. Sweet pickles are not only sweet and sour; they're also salty. Likewise for some vinaigrettes. Generally speaking, when three of the basic tastes are present, one appears as a mere background note, not as prominent as the other two.

Threesomes, you see, are tricky. No, I didn't mean it that way, but now that you mention it, it's not a bad analogy. Even leaving aside the menage à trois types of relationships, friendships among three friends typically require a lot more balancing and effort than do friendships between two people. It's the same with basic taste elements. Adding a third one to a twosome inserts a whole new dynamic; it can be a brilliant success, or a dismal failure.

OTHER FLAVOR CATEGORIES

Now I'm going to venture out past the four basic tastes. We're on much shakier scientific ground here, because researchers don't write about flavor categories the way they do they do about the sense of taste. Chefs and cookbook authors are not much help either. Generally when they mention categories of flavor, they don't offer much in the way of explanation; rather, they assume we know what they're talking about. And even those authors who do explicitly mention flavor categories are not in agreement on what they are. One book lists 14 elements of taste ranging from "bulby" to "spiced aromatic" to "oceanic." Another lists such flavors as "pungent" and "puckery" and other less helpful categories as "intense."

I'm not disparaging these authors' efforts, honestly. It's tough going when you try to categorize flavors. Although I've tried to stick with the sorts of terms that show up regularly in cookbooks, reference books and restaurant reviews, my list is somewhat subjective as well.

Why group flavors into categories at all? Well, it's because we're all human here (I assume) and that's what humans do -- we categorize things. It's the way we learn about the world. So you probably categorize foods without even really thinking about it. Listing some basic categories and analyzing how our foods fit into them is simply a way to harness that usually unconscious process and improve upon it, enhance it, sharpen it.

What follows here is not exhaustive; it's not definitive, but it's a starting point. Keep in mind that not every food falls into one of these categories, and many foods fall into more than one:


  • Earthy: Think mushrooms. Also carrots and other root vegetables, which often also have a sweet dimension as well.

  • Fermented: Wine and beer obviously fall in here, but also sour cream, yogurt, cheese, buttermilk. Some breads, especially sourdough. Soy sauce and fish sauce are both fermented, but the salty taste partially masks the fermented flavor.


  • Herbal: We'll look at herbs and spices in detail in the second part of the course, but for now just think of the clean, "green" scent and flavor of dill, parsley, basil and the like.


  • Meaty: This term is so often used to describe a texture that it's difficult to isolate it as a flavor alone, but that's what I'm aiming for here. So mushrooms, although they can have a "meaty" texture, do not always or even often have a meaty taste.


  • Nutty: Nuts, obviously, but also some grains and cheeses and even avocados have a hint of nuttiness about them.


  • Poultry: No, everything does not taste like chicken, but most of the birds we eat fall into this category. Apparently, so does a mushroom called chicken of the woods.


  • Seafood: The natural name for this category would be "fishy," but that term has such negative connotations that I hesitate to use it. It's used to describe old fish. But fresh seafood and fish do have a common element in their flavor, and that's what I mean by "seafood." (Freshwater fish, although generally milder, also fit in here.)



  • Spicy: This one's tricky. We often use the term to mean "hot" in the sense of chile peppers or horseradish, but as we'll see in the next section, "hot" is not a flavor, it's a chemosensory irritation. So think about "spicy" as what's left over after you remove any of those sensations: usually somewhat bitter, often musty, and always fragrant.


  • Starchy: This is one of those terms that have elements of both taste and texture. Since there's a whole group of foods we commonly refer to as "starches," it's not hard to identify this taste. It's what's common to potatoes and some other root vegetables, rice and corn, to name a few. We'll talk again about starch when we get to textures.


  • Vegetal: Here I'm thinking mostly of green vegetables, and not of the culinary vegetables that are botanically fruit, such as tomatoes, peppers, and squash. Likewise, I wouldn't include roots and tubers like potatoes and carrots here.


  • Toasted/Roasted: Think about the difference between a slice of bread and a slice of toast, or the difference between raw almonds and roasted ones. Basically we're talking about the flavor effects of browning here.


  • Smoked: Cheese or meats, fish or fowl, these foods get their flavor from the smoke they're cured in. They generally also have a salty side, as the curing process usually involves brine or salt.




FLAVOR AND BEYOND

So, now that we have a starting list of flavor categories, what do we do with it? Along with the information on basic tastes, use it to begin analyzing the foods that you cook and eat. As you taste a dish, ask yourself which basic tastes it has, and which flavor categories it belongs to.

"Why?" you may ask, "what's in it for me?" First, if you like to cook, analyzing foods in terms of tastes and flavors (and, as we'll see, textures) can provide you with a lot of knowledge about substituting ingredients and improvising in the kitchen. For instance, suppose I have a recipe that calls for beets and I don't like them. To come up with a workable substitute, it helps a lot to know that beets are sweet, starchy and slightly earthy. What other foods have those attributes? Maybe sweet potatoes. Maybe rutabagas. The point is, I've got a place to start.

Second, the better you get at analyzing at tastes and flavors, the better you'll be at figuring out what's in dishes that you like (or those you don't like, for that matter). Maybe this has happened to you: you're at a restaurant eating dinner. That sauce on your prawns is delicious and you'd really like to know what's in it. Let's face it, you're probably not going to get a recipe from the chef, but if you know your flavors, you can do some experimenting and probably be able to come up with at least a close approximation.

What's even more amazing is that with enough practice, you may even be able to tell not only what's in a dish, but what's missing from it. Suppose you're trying your hand at cooking something new, and it's blander than you expected, or it just needs something. If you've had practice tasting critically and thoughtfully, your chances of figuring out just what that "something" is are much better than if you haven't. You'll be able to think back to similar dishes that did taste good and isolate what those dishes had that your current dish lacks -- garlic, or lemon juice, or salt, or a pinch of sugar. Spices, perhaps. And believe me, if you can rescue bad tasting food, or make average food good, you've got an enviable skill.

So now that you’ve made it through the theory, it's time to practice a little. Take some time to try at least some of the experiments that follow. Start to analyze what you eat and drink. After that, we’ll turn to texture, mouthfeel and chemosensory irritations, but we’re hardly leaving taste and flavor behind. They’ll be coming along for the ride.

EXPERIMENTS

None of these experiments are very difficult or time consuming; most require only a couple of common ingredients to perform. As you read through them, they may, in fact, strike you as terribly simple and obvious. Indeed, they are simple. But to get the most out of them, they do require two things: thought and concentration. If you're going to perform them, take the time to really think about your sensations as you do. You may want to take notes, if that helps you to concentrate.

Temperature and Flavor

Buy two cans or bottles of any one type of juice drink or soft drink, preferably not something with a lot of carbonation. Leave one at room temperature while you chill the other as cold as you can get it (if it's just starting to get a little slushy around the edges, that's perfect). Taste them both and compare. Does the warmer drink taste sweeter? Can you taste other flavors (good or bad) that seem to be missing in the ice-cold drink?

Salt

This requires a kitchen scale. Gather as many different kinds of salt as you can: iodized table salt, non-iodized salt, kosher salt and, if you can find it, at least one of the specialty sea salts: Fleur de Sel, or the gray salt from Brittany or something similar (most of them are French).

By weight, measure out equivalent amounts of each. It's crucial to measure by weight and not by volume, because the different grain size and shape in the various salts result in vastly different amounts of salt per unit of volume. You won't need much, so use the smallest measurement you can. Mix each kind of salt with enough hot water to make a 2 or 3% solution.

Let the solutions cool and taste them. It helps to have some unsalted crackers and some water with a little lemon squeezed in it to "cleanse" your palate between tastes. Can you tell the difference? If so, what is the difference?

Now taste the various salts sprinkled on top of tomato slices. What differences do you experience this time?

Umami

First, run out and buy some monosodium glutamate. The most widely available form of MSG that I know of is Ac'cent; you should be able to find it at any grocery store. (I know, you're thinking, "MSG? Is she serious?" Yes, I do know about everything written concerning MSG. I've read the scary stories. The deal is, it's really difficult for the average consumer to isolate glutamate any other way, and I honestly think a little monosodium glutamate in the diet is not harmful. However, if you're concerned or you think otherwise, by all means skip this experiment.)
Next, dissolve a small amount into a cupful of hot water (hotter than tepid, but cool enough to sip without scalding your tongue). Say, half a teaspoon of Ac'cent to a cup. Sip it and think about it. What's it taste like? What's it feel like on your tongue?

Sweet and sour:

First, make a simple syrup with sugar and water. In a small saucepan, add one cup water and two cups sugar. Heat to dissolve and bring to a boil. Simmer for a couple of minutes and let cool. Meanwhile, squeeze a couple of lemons.

Mix two tablespoons of syrup with one cup water. Taste the mixture. Now, add one tablespoon lemon juice and taste again. What does the addition of the lemon juice do to the sugar water?

Next, start at the other end. Mix two tablespoons of lemon juice with one cup water, taste, and then add one tablespoon of syrup. (You'll have the opposite proportions, obviously.) What do you think of that mixture?
Try different proportions and think about the balance of sweet and sour. What proportions do you like best?

Bittersweet

Get as many chocolates of different sweetness levels as you can find. Many chocolates are now labeled by levels of cocoa mass and cocoa butter. For instance, a chocolate labeled "70 percent" contains that amount of cocoa, with the remaining 30% being sugar and other ingredients (milk chocolate will have the lowest percentage of cocoa and will also contain milk solids). Include unsweetened chocolate (sometimes called "baking" chocolate) as well. Starting with the least sweet, taste them and compare. If you start with unsweetened, it will probably be almost unbearably bitter. As you taste, think about the level of sweetness you prefer.

Now, for part two, get some caramels or caramel sauce. Taste the chocolates again, this time with a small bite of caramel accompanying each taste. How does the additional sweetness alter the chocolate? Do you find your previous favorite too sweet with the addition of the caramel?

Salty and Sour

Scoop out the flesh from a ripe avocado and mash it up. Taste a small bite as a basis for comparison. Divide the remaining avocado into three portions. To the first, add a pinch of salt. To the second, add a squeeze of lemon juice.

Taste the first sample. Now add a squeeze of lemon to the salted avocado. How does it change the flavor? Is the salt more or less pronounced, or is it unaltered?

Taste the second sample (the one with only lemon juice). Add a pinch of salt and taste again. How does the salt affect the acid? Does it make the lemon flavor more pronounced?

Now add enough salt to the third portion to make it taste noticeable salty to you (this could vary quite a bit depending on your tolerance for salt). Add a squeeze of lemon and see if that diminishes the salty flavor.

Sweet and Salty

Make a small batch of popcorn. Divide it into three portions. Sprinkle one with salt, one with sugar, and one with a combination of salt and sugar. Taste the three samples and concentrate on the way the salt and sugar affect each other.

Another way to experiment with salt and sugar is add a pinch of sugar to a savory sauce, such as tomato sauce, and see how it changes the flavor. Or add a pinch of salt to a sweet sauce such as caramel or a custard and see if it intensifies the flavor.

Ask your questions about this course here.

Look out for the announcement of "PART TWO:TEXTURE" soon.

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