1.3 Taste Categories: Myths & Modern Research
According to the text book tongue map above, the taste buds for "sweet" are on the tip of the tongue; the "salt" taste buds are on either side of the front of the tongue; "sour" taste buds are behind this; and "bitter" taste buds are to the rear. (Certain wine glasses are said to cater to this arrangement). Unfortunately, the map itself is wrong. In fact, there are five basic tastes officially recognised so far, and the entire tongue can sense all of these tastes more or less equally.
The Tongue Map Myth
The concept of the classical text book 'tongue map' dates back to last century when a German psychologist at Harvard University, D.P. Hanig was working on a PhD thesis. Hanig's thesis was published in'philosophische studien'in 1901. Hanig's data was misinterpreted for seventy five years (supposedly due to mistranslation), and it was not until 1974 that a paper by Collings re-examined the data and dismissed the theory of the tongue map. Despite this, some quarter of a century later, many textbooks still have not been changed.*
From my own personal observations, I have long being dissatisfied with the very notion of four 'basic tastes'. The model does not account for a host of more complex sensations which the brain seems to interpret as taste. New research has discovered receptors on the tongue capable of identifying the sensation of water and more famously, the "fifth basic taste", 'umami'(also described as 'savoury').Others, including myself, have advanced still more categories of taste. These are outlined below.
The taste of water has only recently been argued as a taste perception.
If water is consumed by humans in a normal manner, that is in the presence of saliva, then the taste of water has been described as flat, bland or tasteless. However, if water is taken up in a medium of citric acid or quinine, then the taste sensation of water has been described as being sweet. On the other hand, if the taste medium of water is either sucrose or sodium chloride (salt) then the reported taste sensations have been described as bitter or sour. Much of the taste perception in humans thus clearly depends upon normal saliva flow, which is the pre-adapting media by which a taste sensation is to be determined. Many people who are undergoing some form of medication will find their ability to taste is altered, due to the fact that some four hundred-odd medications alter saliva flow. The sensations of salt taste and water taste have a dual role, in that they bias the taster to either reject or swallow according to the body's ion / water balance requirements. The body has learnt to reject too much salt just as it has learnt to demand water. These adjustments are initiated by the taste sensory system even before substances are absorbed in the intestine.
Umami / Savoury Tastes
As research has advanced, a taste sensation called "Umami" (pronounced"oo-marmi") has been accepted. It was first identified by Professor Kikunae Ikeda[pictured below]at the Imperial University of Tokyo in 1909. He had observed that "There is a taste which is common to asparagus, tomatoes, cheese and meat but which is not one of the four well-known tastes of sweet, sour, bitter and salty."
It was in 1907 that Ikeda started his experiments to identify the source of this distinctive taste. He knew that it was present in the "broth" made from kombu (a type of seaweed) found in traditional Japanese cuisine. Starting with a tremendous quantity of kombu broth, he succeeded in extracting crystals of glutamic acid (or glutamate, an amino acid and a building block of protein). Ikeda found that glutamate had its own distinctive taste and he named it "umami" - a Japanese noun (literally meaning "delicious flavour").
Umami is now used to designate a pleasant gustatory sensation that is different from sweet, sour, salt or bitter. It is the taste sensation that is most influential in determining how delicious a food is. Sometimes described as "savoury" or "meaty", the same taste is referred to as "xianwei" in Chinese cooking and is considered a fundamental taste in Japanese and Chinese cuisine, but is little discussed in the west. Umami has also been described as a salty, seaweed-like characteristic, especially well defined in certain Scotch Whiskies, particularly those from the island of Islay off the west coast of Scotland. Indeed, the glutamate taste sensation is most intense in combination with sodium. This is one reason why tomatoes exhibit a stronger taste after adding salt.
The active ingredients of umami were initially identified as L glutamate(found in human and chimpanzee milk),other amino acids and small peptides. After this discovery, research investigating the connection between amino acids - a structural element of protein - and the taste of food continued, and it was eventually discovered that each of the twenty kinds of amino acids possesses its own unique taste. The combination of these various tastes is an important element in determining the flavour of foods. Apart from the amino acid glutamate, the umami taste is also given by the nucleotides inosinate, which can be found in meat and fish, and guanylate, which is found in mushrooms. The synergistic effect of these different types of umami has been scientifically proven - that is, that by combining these different kinds of umami, the umami taste is significantly magnified. Examples include onion (glutamate) with veal (inosinate); Chinese cabbage / leak with chicken bones; and Japanese Konbu / kelp with Bonito flakes.
Glutamate is naturally present in most foods, such as meat, poultry, seafood and vegetables as are the two kinds of nucleotides that contribute most to the Umami taste, inosinate and guanylate. Inosinate is found primarily in meat, whereas guanylate is more abundant in plants. Another nucleotide, adenylate, is abundant in fish and shellfish. The foods listed below contain high quantities of Umami elements:
* Katsuobush/Dried bonito flakes
* Niboshi/Small dried sardines
* Sea bream
* Shiitake mushrooms
* Enokitake mushrooms
* Soy beans
* Sweet potatoes
* Chinese cabbage
* Parmesan Cheese
* Green tea
It may be conjectured that having a critical need for protein, with amino acids being the building blocks for protein, our taste for umami drives our appetite for high protein foods like meat. Bacon, for example, incites a strong umami sensation because it is a rich source of amino acids. On the tongue, it appears that a subset of savoury taste buds responds specifically to glutamate in the same way that sweet ones respond to sugar.(For more information regarding umami, including recipes and the latest research updates there is now an official website dedicated to the fifth taste:www.umamiinfo.com)
Trigeminal Flavours or "Mouthfeel" Sensations
A further addition to the emerging new model of taste is a more generalized chemical sensitivity in the mouth, which in fact exists over the whole body (even mucus membranes in the anus are sensitive giving rise to the old Hungarian saying that "good paprika burns twice"). In the mouth, this general chemical and tactile irritability is primarily mediated by the trigeminal nerves in the tongue.(Also called the 'fifth' nerve, the trigeminal nerve is one of the twelve paired nerves that originate in the brain stem. It is both the main sensory nerve of the face and also has certain motor functions including biting, chewing and swallowing).
One isn't required to be an experienced wine taster in order to appreciate the significance of trigeminal stimulation or 'mouthfeel': Everyday experiences include the fizzy tingle of CO2 in carbonated drinks, the burn from hot peppers and spices such as ginger and cumin, the tastes of chemical compounds, alcohol, tannins and alkaloids, fats and oils, as well as tactile sensations of pain, texture, temperature, electricity. All of these sensations can be experienced in various parts of the mouth, contributing to the overall sensation of 'flavour'. Taste buds appear organized to provide trigeminal access to the oral milieu with trigeminal fibers ascending around the taste bud forming a chalice-like structure. The trigeminal endings seem to use the specialized structure of the taste bud to find a channel to the external environment. This speculation is consistent with the observation of high responsiveness to pepper chemicals in areas such as the top of the tongue that are rich in fungiform papillae.
However, with mouthfeel, the distinction between a chemical sense and a tactile sense becomes somewhat blurred for the reason that the nerves in question mediate tactile, thermalandpain sensations. This blurring is perhaps best illustrated by sensations of astringency, a familiar characteristic of some red wines. Tannins in wine (and food) are chemical stimuli and yet the astringent sensations they produce seem largely tactile. They make the mouth feel rough and dry, and cause a drawing, puckery or tightening sensation in the cheeks and muscles of the face. Although scientific analysis would categorise astringency as a group of chemically-induced oral tactile sensations, most wine tasters would say that astringency is an important component of wine "flavour." This highlights, once again, the integrative nature of flavour in combining inputs from multiple sources.
The mechanisms giving rise to these sensations are not completely understood, but one long-standing popular theory has it that tannins bind to salivary proteins and mucopolysaccharides (the slippery components of saliva), causing them to aggregate or precipitate, thus robbing saliva of its ability to coat and lubricate oral tissues. One feels this result as rough and dry sensation on oral tissues, even when there is fluid in the mouth. Note that "roughness" and "dryness" are difficult to perceive unless a person moves the tongue against other oral tissues (which we do all the time when eating). **
If we observe our own sensations of wine and food carefully we will note that tongue and mouth receptors are capable of determining many more sensations than those already outlined (salt, sweet, acid, bitter, water & umami). I have attempted to classify these in the following paragraphs as either "taste" or "mouthfeel". For example, I have included the sensation of pressure. Whilst pressure arguably contributes nothing to taste, it cannot be disputed that pressure is a part of mouthfeel. For a wine taster, pressure is a 'taste' sensation because of its influence in creating the sensation of 'gas release' in the mouth, which differentiates the various Champagne qualities and styles. An experienced Champagne taster can pick up pressure in the mouth and recognise the difference between a carbonated, tank fermented and bottle fermented sparkling wine. This recognition is based upon the size of the bubbles and their impact in the mouth. On the other hand, an experienced taster of sparkling wine can also tell when a wine has sufficient pressure, too much pressure or too little pressure. So for these reasons, pressure is incorporated as a category. No doubt my classification is controversial. There are many fine points for the academics and scientists to debate.
Tastes can be defined within primary, secondary or tertiary categories.
Primary Taste Sensations
These belong to the unprepared, or unaltered grapes, fruits, vegetables etc, and indicate the taste sensation that one would experience if one was to taste the produce in its unprepared state. For example, winemakers not only test for chemical ripeness of grapes, i.e.- sugar levels, acidity, pH etc, but they taste the grapes to experience the flavour development, even though the sweetness of a grape may have quite a different taste sensation from the sweetness of the finished wine.
Secondary Taste Sensations
These are the taste sensations that most people experience and are the modified taste sensations which have resulted from winemaking practice, food preparation or cooking. For example, the sugar from a grape can be entirely converted into alcohol, thus creating a dry beverage. Alternatively, fermentation can be arrested creating a sugary sweet wine. Semillon and Riesling are two classic grape varieties which can produce grapes and wine with a variety of sugar levels. Acidity will also be different, which will reflect different degrees of ripeness.
Tertiary Taste Sensations
Tertiary taste sensations, like tertiary aromas, develop or are modified over time. A young wine might start out with very high levels of acidity but over the years, this acidity could drop off to the point where the wine tastes 'flat' or 'dull'. The taste sensations of sweetness can also be modified overtime. A Sauternes might have a very high degree of sweetness as a young wine whilst as an old wine it will become significantly drier.
Major Taste Sensations
(i) - fruity (moselle)
(ii) - semi sweet (spatlese)
(iii) - sweet (auslese)
(iv) - very sweet (beerenauslese)
(v) - sugar sweet (troken beerenauslese)
(vi) - cloying
(vii) - sugar
(viii) - honey
(ix) - treacle
2. ACID TASTE SENSATIONS
(i) - sour
(ii) - acetic
(iii) - acid
- - - a. citric
- - - b. lactic
- - - c. malolactic
3. ALKALINE TASTE SENSATIONS
(i) - powdery
(ii) - furry
(iii) - mouthcoating
(v) - astringent
4. BITTER TASTE SENSATIONS
(i) - quince
(ii) - astringent
(iii) - chemical bitter
(iv) - phenolic bitter
(v) - cyanide
5. UMAMI TASTE SENSATIONS
(i) - glucomates
(ii) - seaweed
(iii) - chicken broth etc.
6. SALT TASTE SENSATIONS
(i) - dilute
(ii) - sea salt
(iii) - table salt
(iv) - rock salt
(v) - mineral salt
(vi) - vegetable salt
7. DRY TASTE SENSATIONS
(i) - sweet dry (oloroso sherry)
(ii) - medium dry (amontillado sherry)
(iii) - dry (fino sherry / brut )
(iv) - very dry (manzanilla sherry)
(v) - bone dry
8. WATER TASTE SENSATIONS
(i) - mountain water
(ii) - tap water
(iii) - hard water
(iv) - mineral water x location
(v) - soda water
(vi) - dank, polluted water
(vii) - salty water
(viii) - chemical contaminated
(ix) - medicinal
9. CHEMICAL TASTE SENSATIONS
(i) - various chemical compounds
(ii) - medicines
(iii) - chemical extracts
10. FAT & OIL TASTE SENSATIONS
(i) - soapy
(ii) - vegetable fats and oils by variety
- - - peanut oil
- - - olive oil
- - - sunflower etc
(iii) - animal fats and oils by species
- - - bird domestic
- - - game bird
- - - domestic animals
- - - wild animals, etc
A Note on Fats & Oils...
In discussions regarding taste, it has always struck me as odd that fats and oils seem largely omitted, apart from being used to describe the viscosity of a liquid. (Old Alsatian Gewurztraminers, for example, can be described as 'oily', yet this pertains more to mouthfeel than taste). And yet research indicates that the taste buds are fine-tuned to detect sweet foods which have a very high calorific value, and therefore in the survival game are of great importance. Possibly the reason for the omission from the discussion of fats and oils is their complex molecular structure which is difficult to explain in lay terms. Fats and oils are the most concentrated source of food energy. They provide 9 Kcal of energy per gram which is approximately double the energy provided by proteins or carbohydrates. They are carriers of fat-soluble vitamins and they contribute to food flavour and palatability as well as the feeling of satiety after eating. The question is then to be asked, where does the taste sensation of fat occur in the mouth? A basic understanding of the characteristics of fats and oils will assist us in determining their role in the taste sensations.
Fats and oils are classed into five characteristic groups:
10.1 MILK FAT GROUP. (This relates to milk of the cow, water buffalo, sheep, goats, etc.)
Milk fat is particularly susceptible to variations as a consequence of the animal diet (pasture, feed etc.), time of year, type of grass, quality of water etc..
10.2 LAURIC ACID GROUP
The most widely used are coconut, seeds of the oil palm and coquilla nut. These generally melt at low temperature due to the short carbon chains.
10.3 THE OLEIC - LINOLEIC ACID GROUP
This is the largest and most varied group and contains only fats and oils of vegetable origin. They contain less than 20% saturated fatty acids, with oleic and linoleic acid being dominant. These fats are derived from seeds of cotton, corn, sesame, peanut, sunflower, safflower, and fruit pulp of olive and oil palm
10.4 LINOLENIC ACID GROUP
The Linolenic acid group contains substantial amounts of linolenic acid, but also also high levels of oleic acid and linoleic acid. The most important source is soybean, but it may also be found in the oils of wheat germ, hempseed, perilla and linseed. The high linolenic content contributes to the drying oil characteristic e.g. linseed oil.
10.5 ANIMAL FAT GROUP
The animal fat group consists of lard from the pig and tallows from bovine and ovine sources. This group is characterised by 30-40% C16 and 30/40% C18 -these are saturated fatty acids- and up to 60% oleic and linoleic acid. Fat from sheep, goats, goose, duck, chicken, quail etc, all have their own characteristic taste and, like the milk of cows, this taste is very much dependent upon diet, season, environment and water. The melting point of the animal fat group is relatively high. The fat from wild plants and animals is different from that of domesticated plants and animals. This is again dependent upon management regimes, clonal selection, environmental considerations (indoors or outdoors), season, and water quality. There is no doubt that a wild duck tastes completely different from a domestic duck. The animal fat group consists of the following components:
(Refers to the number of carbon atoms)
All these fats have different melting and boiling points. Fats and oils seem to be discernible at the top of the hard palate. After finding their way there and 'sticking to it' they are moved around by the action of the tongue and in particular, the top of the underside of the tongue. Recent research has revealed a potential taste receptor called the CD36 receptor to be reacting to fat, more specifically, fatty acids. This receptor was found in mice, but probably exists among other mammals as well. In experiments, individual mice not having the receptor (due to a genetic defect) didn't show an unusual urge to consume the fatty acids that other mice did. Mice missing the receptor also failed to prepare gastric juices in their digestive tracts to digest fat. This discovery may reveal a better understanding of the biochemical reasons behind this behavior, although more research is still necessary to confirm the relationship of CD36 and the cravings of fat.
11 . ALCOHOL TASTE SENSATIONS
(i) - dilute
(ii) - soft
(iii) - smooth
(iv) - warm
(v) - hot
(vi) - rough
(vii) - dirty
(viii) - burning
12. TANNIN TASTE SENSATIONS
a... wood tannin - - b... grape tannin
(i) - velvet smooth
(ii) - soft
(iii) - fine grained
(iv) - coarse
(v) - firm
(vi) - furry dry
(vii) - very firm dry
(viii) - excessive
Neutral Wine..... 0 - 1 Second
Cask Wine..... 1 - 3 Seconds
Commercial Wine..... 3 - 4 Seconds
Good Commercial Wine..... 5 - 6 Seconds
Complex Wine..... 8 - 10 Seconds
Very Complex Wine..... 10 - 15 Seconds
Multilayered Wine..... 15 - 20 Seconds
Memorable Wine..... 20++ Seconds
Major Mouthfeel Sensations (Trigeminal Flavours)
As mentioned above, these are technically not 'tastes' but belong to the sense of touch and augment the overall perception of flavour in the mouth. Nevertheless, their significance should not be underestimated. Considering CO2 alone as a trigeminal flavour, the carbonated beverage industry which includes soda, beer and sparkling wine production, amounts to billions of dollars in annual sales of 'trigeminal flavour' worldwide. Similarly, the pepper business and so-called ethnic foods have experienced rapid growth in the West due to a continuing influx of immigrants from cultures with hot, spicy cuisines, and a growing trend toward more adventurous dining on the part of many Westerners. (Salsa was outselling ketchup in the U.S. as early as 1992).
Researchers at Canada's Brock University have made a study (2008) to define wine taste by a range of textures rather than aromas and flavours, thus accentuating the importance and understanding of the mouthfeel. They have devised a vocabulary based on familiar liquids, foods and household materials they feel best describe the wide range of textures experienced in wine. The Australian Wine Research Institute has also created a flavour wheel based upon red wine mouthfeel.
1 . CAPSICUM SENSATIONS (also referred to as "false heat" & "spiciness".)
(i) - white pepper
(ii) - black pepper
(iii) - capsicum
(iv) - hot pepper
(v) - chilli pepper ***
Substances such as ethanol and capsaicin cause a burning sensation by inducing a trigeminal nerve reaction together with normal taste reception. The two main plants providing this sensation are chilli peppers (those fruits of the Capsicum plant that contain capsaicin) and black pepper. Due to lack of a specific word for this flavour in English ("hot" properly refers to temperature; "spicy", to any spice), the French term 'piquant' is occasionally used. The term pungent is also used for this, especially among people of Anglo-Indian ethnicity. Indeed, many languages have a specific term.
2. MENTHOL (also referred to as "false coolness".)
Some substances activate cold trigeminal receptors. One can sense a cool sensation (also known as "cold", "fresh" or "minty") from spearmint, menthol, ethanol or camphor for example. The reactions behind this sense are analogous to those behind the hot sense.
3. ELECTRICAL SENSATIONS
(i) - tingle
(ii) - tang
(iii) - jolt
4. TEMPERATURE SENSATIONS
(i) - ice cold
(ii) - cold ..... 4 Degrees Celsius
(iii) - chilled ..... 8 Degrees Celsius
(iv) - cellar temperature ..... 14 Degrees Celsius
(v) - room temperature ..... 21 Degrees Celsius
(vi) - luke warm
(vii) - warm
(viii) - hot
(ix) - very hot
(x) - boiling ..... 100 Degrees Celsius
Temperature is an essential element of human taste experience. Food and drink which - within a given culture - is considered to be properly served hot is often considered distasteful if cold, and vice versa.
5. TEXTURAL SENSATIONS
(i) - watery
(ii) - thin
(iii) - medium body
(iv) - creamy
(v) - buttery
(vi) - luscious
(vii) - viscous
(viii) - texture
6. PAIN SENSATIONS
(i) - tinge
(ii) - tingle
(iii) - mild
(iv) - medium
(v) - long
(vi) - intense
(vii) - unbearable
Chinese cooking includes the idea of "mÃ¡," the sensation of "tingling numbness" caused by spices such as Sichuan pepper.
7. PRESSURE SENSATIONS
(i) - spritzig
(ii) - carbonated
(iii) - cremant
(iv) - sparkling, methode champenoise
(v) - flat
While the number of accepted taste sensations will undoubtedly continue to be added to, the tongues sensitivity is meager compared with that of the nose. Our olfactory system has at its disposal fifty million plus chemo-receptors. The number of odours recognisable by humans remains a matter of debate; the combinations at least, are likely to be infinite. Olfaction remains the last sense to be explained by science and its ongoing study forms the subject of the remaining chapters in this section.
* See for example, "The Encyclopedic Atlas of the Human Body", a major visual guide published by The Five Mile Press. An edition as recent as 2004 still promotes Hanig's tongue map.
** Information regarding Trigeminal flavours adapted from: Trigeminal Response, Cornell University 2006. Excerpted from H.T. Lawless (1996) Flavor.Ch.8 in Cognitive Ecology, Academic Press (pp. 325-380)
*** The various degrees of pepper heat were broken down in more detail by Wilbur Scoville in 1912, in his "Scoville scale", however it must be remembered that heat values for any given species of pepper will vary considerably depending upon seed lineage and growing conditions.
1. Bartoshuk, L. M. 1993. The biological basis of food perception and acceptance. Food Qual. Pref. 4:21-32
2. Boring, E. 1942. Sensation and perception in the history of experimental psychology. New York: Academic Press
3. Collings, V. B. 1974. Human taste response as a function of location of stimulation on the tongue and soft palate. Percep. Psychophys. 16:169-74
4. Hanig, D. P. 1901. Zur psychophysik des geschmacksinnes. Philosophische Studien 17:576-623
5. Some information regarding umami adapted from the official website dedicated to the fifth taste: www.umamiinfo.com