Oral sense of Touch… (and a bit of Hearing)
from LIFE THE SCIENCE OF BIOLOGY 2007
We’ve been through most of the important 5 senses taking part on wine tasting: Sight, Smell, Taste, including a light “touch” on the sense of Touch, since touch plays a key role in experiencing taste it “deserves” a separate chapter.
Oral touch sensations, include those generated by pressoreceptors, mechanoreceptors and thermoreceptors sensory cells of the oral cavity.
The bodily sense of touch is the first sense to develop. It supplies, major means of information from the proximal environment. The human hand is one of the most important adaptations in our evolutionary history, mainly because we are the only primates able to perform opposition between our thumb and the fingers allowing us the ability to perform minute highly accurate digital manipulations.
The Oral somatosensation plays a crucial role in many aspects of our multisensory perception of food wine and flavour sensation. The tactile stimulation we receive in our mouth supplies informs of food and beverage from the temperature of a food through to its texture. Food texture has been defined by Bourne as: ‘the response of the tactile senses to physical stimuli that result from contact between some part of the oral cavity and the food’. Other researchers included the contribution from other senses, like olfaction, vision, even hearing, and kinesthesia in their definitions, (Kinesthesia is the awareness of the position and movement of the parts of the body using sensory organs). In terms of describing texture of food or wine, these may appear sticky, grainy, sandy, smooth, creamy, harsh, spicy hot or temperature changer (hotter or colder than our body temperature), all of these are felt in the mouth.
When it comes to the tactile experiences associated with the consumption of food and drink, they are obviously important. Oral-somatosensation is recognized as taking a major role in our overall experience of food and drink.
The multisensory aspects of texture
It is, however, not always so easy to ascertain exactly which sense is actually doing the work in terms of giving rise to specific aspects of our multisensory experience of food and drink. We assume that the experience of bursting bubbles of fizzy drinks in the mouth is due to the CO2 bubbles popping in the oral cavity, it turns out that sensation of carbonated or fizzy bubbles on our tongue is not solely tactile but rather a result of the stimulation of the sour taste receptors on the tongue. The perception of fattiness in a food or drink is sensed by tactile receptors, However these sensations do not solely come just from the ability of the oral-somatosensory receptors to sense texture of food or drink consistency, but an accumulation of perception from the olfactory and gustatory receptors. Wine astringency or phenols in fruits and vegetables like brewed tea leaves, squeezed pomegranate or tannins of young red wine, is actually a tactile sensation, although many think of it as part of the wine taste and flavour.
Oral touch sensation is also responsible for the sensation of what we call “mouth-feel”. A menthol candy may evoke a cool mouthfeel sensation, a bite on a hot chilly evokes a burning sensation, alcohol evokes heat sensation etc. Jowitt defined mouth-feel as: “the textural attributes of a food or beverage responsible for producing characteristic tactile sensations on the surfaces of the oral cavity.” (Jowitt, R., “The terminology of food texture”. Journal of Texture Studies, 5:351-358, 1974)
“The tactile stimulation of the oral cavity is also very important for another reason: it turns out that where we localize a tastant follows the location of the tactile stimulus drawn across the tongue and not the point where the taste stimulus itself happens to have been transduced on the receptor surface, the fact that people localize the flavor of food to their mouth, despite the fact that the majority of the information concerning flavour comes from their nose i.e. smell. So smell is likely to attribute in large part to the tactile stimulation that they experience in their oral cavity while eating”
There is also a connection between temperature and taste. Researchers found that simply by raising or lowering the temperature at various surface points on a person’s tongue, temperature changes elicit sensations of sweet, sour, salty and bitter – that is, the four main basic tastes.
Touch sensation and information regarding food or liquid in the mouth are transferred to the brain by means of the Trigeminal nerve (), which projects directly to the primary somatic sensory cortex. This projection carries information concerning touch, texture (mouth-feel), temperature, and proprioception (not to mention nociception or oral pain, and chemical irritation) from the relevant receptors in the mouth. All appear to be represented in the Orbito frontal cortex as well as in several other brain areas.(from: Food Texture and Viscosity: Concept and Measurement M. C. Bourne 1981)
The entire oral cavity has various degrees of the sense of touch, but the parts most sensitive to the “tactile impressions” of wine are the upper, centre part of the tongue and the soft areas of the palate, the inner upper lip, the pharynx, the larynx and the gums. The centre of the tongue contains the filiform papillae (singular: papilla) are one of the four types of lingual papillae (see: https://wine4soul.com/2013/03/16/sense-of-taste-and-wine/ ), they are small prominences on the surface of the tongue.
The Filiform papillae are thin, long (upside-down) “V”-shaped cones that don’t contain taste buds but are the most numerous, covering most of the dorsum (upper surface). These papillae are mechanical and are not involved in taste sensation, but tactile sensation only. Swirling wine in the mouth is a second stage (after sniffing) which helps to pinpoint the sensations of wine texture, temperature, astringency, body alcohol content and the “touch” from carbon dioxide in sparkling wines.
Wine Body: is a tactile term which expresses the feeling of weight of a wine in the mouth. At times the impression of full-body is almost like that of a solid substance even thought we are concerned with a liquid. It is created mainly by alcohol sensation which may lean to the “heavy” side due to higher viscosity than the water constituent of wine the higher the alcohol content the “fuller bodied” the wine . Wine dissolved solids (sediments before settling) also contribute to the sensation of “body” in the mouth.
Wine Texture: this refers to the touch of a wine, how it feels in the mouth. It includes sensations such as smoothess, viscosity; watery or rich dessert wines and is with high combination of sugar, glycerin or the “touch of alcohol.
Wine Astringency: caused by high concentration of phenolic substances in young red wines, responsible for the “dry” sensation caused mainly by the tannins present in the wine at this stage. The ageing process reduces astringency due to oxidation, and will be less evident in mature or older wines.
Temperature: refers in this context to the sensation of warmth created by ethyl alcohol, which increases with the wine’s strength.
Fizziness: a prickly sensation is caused by the presence of carbon dioxide bubbles.
Mechanical characteristics are subdivided into the primary parameters of hardness, cohesiveness, viscosity, elasticity, and adhesiveness, and into the secondary parameters of brittleness, chewiness, and gumminess. Since popular terms are used to describe texture they often point only to a degree of intensity of these characteristics rather than an objective description.
Studied showed that: The in-mouth “chalk-like” texture of wine was strongly associated with anthocyanin concentration and was negatively associated with alcohol level and acidity. The astringent sub qualities of “velvet-like” or “emery-like” roughing were mostly related to polyphenol levels. Wines that elicited a “puckery” sensation were characterized by relatively low anthocyanin levels, high acidity, and high pigmented polymer and tannin concentrations. So both acidity anthocyanin and alcohol concentrations affect tactile sensitivity and perception. As currently defined, wine taste sensations fall into four, or possibly five categories: sweet, sour, salty, Phenolic compounds include several hundred chemical compounds that strongly influence taste, color, and mouthfeel. Tannins and anthocyanins pigments. Some of these are naturally present in the fruit and some are created during the winemaking and aging processes. Phenolic compounds such as Resveratrol have been linked to many of the health-beneficial properties of grapes and grape products.
In the case of wine or juice, mouthfeel combines sensations related to the product’s viscosity as well as sensations related to the product’s chemical properties, such as astringency
Sulfites are sulfur-based compounds occur naturally during wine fermentation, but are also often added before, during, or after fermentation as sulphur dioxide (SO2), to protect wine from oxidation and the activity of undesirable microorganisms, particularly bacteria. Sulfites are added at higher levels to white and/or sweet wines to prevent browning and/or spoilage.
Methoxypyrazines are a class of chemical compounds that produces herbaceous odors (e.g,. green bell pepper, leafy, or vegetative). In white wine, the odors can be desirable. However, in red wines high levels of methoxypyrazines are very undesirable. Although this is an element of “flavour” it has an influence on our mouthfeel of wine touch…
Press play to hear music, music by Daphne Sarnat – http://daphodil-music.co.uk/
To include all 5 senses in the experience of wine drinking or wine tasting the sense of Hearing is added in the form of the hearing ringing sound of glasses touching at the raising of a glass, wine glasses toasting is a very closely observed part of drinking culture. In company, no one should drink a sip of alcohol before having toasted every other person at the table by touching each others glass with intention a look into each other’s eyes… the talk around the table about the wine being drunk or tasted, sound of a popping champagne bottle, wine being poured into a wine glass, and the sound of a wine glass or God forbid… a wine bottle shattering in the background. All thought the ear our hearing sense organ with it’s center and specialty sense receptors in the Middle ear connected to our brain via the Auditory nerve – Cranial nerve Number 8.
All of our 5 senses take part during wine drinking, appreciation, and wine tasting. All of these arise in the head area; they all have specialty sense organs which are connected to our brain via one or more of the 12 Cranial nerves sometimes simultaneously by several cranial nerves. What a wonder our body is, what a wonder wine is…it is indeed a symphony of senses (see: https://wine4soul.com/2012/05/11/symphony-of-senses/ )
Drink, Sense, Enjoy.
Anatomy and physiology of the sense of Taste (Gestation), in wine tasting (Part 1)
(Anthelme Brillat-Savarin, writer of: “The physiology of taste”, French gastronomer- the “father” of Food Writing. (1755-1826)
Taste is another sense which communicates knowledge of our surrounding to the brain. Multiple cranial nerves, including cranial nerves VII, IX and X, transmit taste information from the mouth and pharynx to the brain via the brain stem. Cranial nerve V is responsible for the oral sense of touch which with the sense of smell are complimentary to the overall sense of flavour.
ANATOMY and PHYSIOLOGY of TASTE
The sense of taste is one of the five senses. Taste is the sensation produced when a substance of certain chemical properties reacts chemically in the mouth with the chemo-receptors of the taste buds on the tongue.
Wine like any other food or beverage, consumable product, affects our sense of taste and smell through the chemical effect of its constituents on the chemoreceptors of the smell and taste sense organs. The sense of taste is basically our ability to sense and react to soluble molecules and Ions called tastants –or taste emitting products.
Although there are five different types of taste receptors known: salt, sweet, sour, bitter, and Umami, Since there are very few salty or savoury, (Umami) wines tastes, wine is manifested taste wise, only as one of the 3 primary tastes: sour, sweet, bitter. Or their combined tastes.
All of our taste receptors are located in the oral region and most of those, are on the tongue. These receptors are known as taste cells, and they are contained in bundles called taste buds, which are contained in raised areas known as papillae. They are located on the upper surface of the tongue, soft palate, upper esophagus and epiglottis.
There are four types of papillae present in the human tongue:
• Fungiform papillae – these are mushroom-shaped protrusions that make up most of the coating of the dorsal surface of the tongue, as well as at the sides contain taste receptors and Innervated by the Facial nerve (cranial nerve 7)
• Foliate papillae – these are ridges and grooves towards the back part of the tongue on both sides. They contain taste receptors and are Innervated by facial nerve (front papillae) and glossopharyngeal nerve (papillae at the back).
• Circumvallate papillae – there are around 12 of these papillae in most people, and they are present at the very back of the tongue, and form the far border of our tongue. These papillae are associated with the ducts of Von Ebner’s glands, contain taste receptors and are innervated by the glossopharyngeal nerve.
• Filiform papillae – these are thin, “V”-shaped cones, elongated papillae that do not contain taste buds and are not involved in gestation, but are the most numerous. These papillae provide mechanical reception (sense of touch). They are characterized by increased keratinization contributing to the roughness of the tongue surface and probably an evolutionary remnant that allows “scraping meat remains” off bones (highly evolved in the Cat family)
Each taste bud houses gustatory cells that control the function of taste sensation. Soluble food particles dissolved in the saliva, flow into the taste bud and the cells react. Nerve signals are sent to the brain and reach the gustatory section of the sensory cortex, the so-called taste center.
The primary gustatory cortex is a brain structure responsible for the perception of taste the: anterior insula on the insular lobe and the frontal operculum on the inferior frontal gyrus.
There are some 10,000 little taste buds on our tongue that perceive the taste of food and wine. Once signals reach the taste center, the brain interprets the food by its tastes as good or bad. Chewing food also sends volatile molecules of food via the Nasopharynx to the olfactory center in the nose which is interpreted as smell. Taste and smell receptors send signals to the brain, which simultaneously is translated as flavour (combined smell and taste) in the brain. Nasal congestion may diminish the sense of taste (inability to smell essentially obliterates the sense of taste).
The cerebellum, or the forebrain, controls taste buds. Sensory neurons from the tongue send electrical impulses to the brain to determine a substance’s taste. The “primary gustatory region” is located just behind the temporal lobe.
Cranial nerves associated with taste are: Cranial nerve VII – Facial nerve controlling the front 2/3 tongue , Cranial nerve IX – glossopharyngeal nerve the back 1/3 of the tongue , Cranial nerve X – Vagus the Epiglottis
Taste unlike the sense of sight (Optic nerve), or hearing (Auditory nerve) which are large, visible bundles of neurons with all sensory information carried through them to one center in the brain (sight or hearing), utilizes several cranial nerves to take part in transforming the stimuli none of which is doing so as its primary function.
Taste (gestation), along with smell (olfaction) and trigeminal nerve sensation of touch (the sensation of texture, pain, and temperature), determines flavors, the sensory impressions of wine or other substances.
Taste Buds Structure:
The bud is formed by two kinds of cells: supporting cells and gustatory-taste cells.
The supporting cells form an outer envelope for the bud. Some are found between the taste cells.
The gustatory (taste) cells are spindle-shaped, and each possesses a large spherical nucleus near the middle of the cell, with a chemoreceptor, that occupies the central portion of the bud.
Each cell ends up at the gustatory pore (hole) in a fine hair filament, the gustatory hair. Soluble chemicals in the saliva affect the receptors and give rise to a certain taste sensation.
Wine is a special drink in the sense that it is revealed taste wise in layers of exposure, it contains 3 of the 4 tastes whether directly sweet, sour and bitter or in case of very dry wine (there are still 4gr of sugar /Liter) sweetness can often be felt by association.
Although each bud contains receptors to all tastes there are zones on the tongue sensitive to one of the 5 tastes in particular.
Sweet sensation is located mainly at the tip of the tongue (front).
Salty sensation are around the sweet zone.
Sour sensation: acidic foods like vinegar or lemon are located along both sides of the tongue
Bitter taste: alkaline foods like quinine or unsweetened coffee are located at the base of the tongue (far back)
Sweet sensation is produced by the presence of sugars. At least two different variants of the “sweetness receptors” must be activated for the brain to register sweet sensation. The average human detection threshold for sucrose is 10 millimoles per liter. For lactose it is 30 millimoles per liter.
Sourness is the taste that detects acidity. The sourness of substances is rated relative to dilute hydrochloric acid; Sour taste is detected by small groups of cells that are distributed across all taste buds in the tongue. The most common food group that contains naturally sour foods is fruit, such as all citrus especially lemons, tamarinds, grapes. Wine also has a sour tinge to its flavor, and if not kept correctly, it will spoil and attain the sour taste of vinegar.
Saltiness is a taste produced primarily by the presence of sodium ions. Other ions of the alkali metals group also taste salty.
Bitterness is the most sensitive of the tastes, and many perceive it as unpleasant, sharp, or disagreeable, but it is sometimes desirable and intentionally added via various bittering agents. Common bitter foods and beverages include coffee, unsweetened cocoa, olives, citrus peel. Quinine is also known for its bitter taste and is found in tonic water. A large number of natural bitter compounds are known to be toxic. The ability to detect bitter-tasting, toxic compounds at low thresholds is considered to provide an important protective function. Taste receptors, type 2, also known as T2Rs coupled to the G proteingustducin are responsible for the human ability to taste bitter substances.
Umami is a savory (appetitive) taste described as meaty taste. Monosodium glutamate (MSG), produces a strong Umami taste It can be tasted in cheese, soy sauce, meats and in many other fermented and aged foods. Some say that Umami taste buds respond specifically to glutamate in the same way that “sweet” ones respond to sugar. Glutamate binds to a variant of G protein coupled glutamate receptors.
Others say that Umami is not one of the primary tastes but rather a “taste” evoked by conditioning and is a result of a learning process. When we eat proteins they are broken through digestion into amino acids one of which is Glutamate. Glutamate receptors in the “in our intestine” sense glutamate and send signals to the brain regarding Protein consumption which is connected to the meat, cheese, eggs we have just consumed and since proteins are required as body building materials the brain “makes us like” them through glutamate receptors in the gut and not on the tongue – taste receptors. We learn to like body builders essential to our body, same goes with fats, fats are tasty because our body needs them not because they have taste.
The sense of taste and olfaction are connected to our emotional state as well as their chemical effect on the chemo receptors and their proximity to the “emotional and memory centers” in the brain.
On Gustation and wine tasting in particular on my next anatomy and physiology post