Tagged: physiology of smell
The scent of wine (Part one)
The Anatomy and physiology of Olfaction-(smell) in Wine Tasting,
The sense of Smell – Sense No. 2 in wine tasting.
Cranial nerve No. 1 the Olfactory nerve.
Smell refers to 1: Olfaction, the actual act of smelling an odor, or 2: odor, as simply the smell that is being emitted by vaporized molecules of a volatile material.
It is through the aromas of wine that wine is tasted. The human tongue is limited to the 5 primary tastes perceived by taste receptors on the tongue: sour, sweet, salty, bitter and Umami, so if an orange is sweet and sour and a strawberry is also sweet and sour, it is the “sweet and sour” with an orange or a strawberry aroma that distinguishes between the two. Taste and aroma together – Flavour, is the final interpretation of consumed food or beverage in our brain. Of the five senses, smell is of the highest sensitivity, approximately 10,000 times more sensitive than the sense of taste. The part of smell in what we define as flavour is 75% smell (olfaction) and 25% taste. Since smell is 10,000 times more sensitive than taste it requires that amount less Chemical Stimuli to be manifested clearly in the brain.
The wide array of fruity, vegetal, earthy, floral, herbal, mineral woody and other flavours perceived in wine are derived from aroma notes interpreted by the olfactory bulb. In wine tasting, wine is often smelled before being drunk in order to identify some components of the wine that may be present. Different terms are used to describe what is being smelled. Aroma can be referred to as “pleasant” even alluring smell as opposed to odor which is referred to as unpleasant or repelling smell (mainly found in wine faults). The term aroma maybe further distinguished from bouquet which generally refers to the smells that arise from the chemical reactions of fermentation and aging of the wine as it ages in the bottle (tertiary aroma).
Smell (or Olfaction) allows humans and other living organisms with smell receptors, to identify their food, mating partner and warn against approaching enemies, it provides both sensual pleasure (the odor of the opposite sex, flowers and perfume) as well as warnings of danger from spoiled food, nearby predators and chemical hazards: toxins and poisons. It is a means by which all living creatures communicate with their surroundings and environment.
The sense of smell is a direct chemical sense, but in order to smell any product, it must be Volatile so that vaporized molecules from it penetrate through the nose, and reach the center is the odor in the nose, the olfactory bulb.
Everything we “smell”: from flowers, vegetables, fruit, baking odors fragrances, perfumes, to even putrid chemicals, are volatile chemical molecules i.e. molecules dissolved as gas vapors in the air. These come to “contact” with the smell center in the upper roof of our nose. Only highly volatile materials are distributors of smell that affect the olfactory bulb our smell center.
General Physiology of Olfaction: The smell sense organ and the OLFACTORY NERVE (Cranial Nerve No.1)
Odorants are volatile chemical compounds that are carried by inhaled air to the Regio olfactoria (olfactory epithelium) located at the roof of the two nasal cavities of the human nose. The olfactory region of each of the two nasal passages in humans is a small area of about 2.5 square centimeters containing in total approximately 50 million primary sensory receptor cells. This is not so many in comparison to a rabbit : 100 million of these olfactory receptors, or a dog: 220 million. Humans are nonetheless capable of detecting certain substances in dilutions of less than one part in several billion parts of air. An odorant must possess certain molecular properties in order to provide sensory properties. It must have some water solubility, a sufficiently high vapor pressure, low polarity, an ability to dissolve in fat (lipophilicity), and surface activity (these are all physical terms) The sense of smell is able to distinguish among a practically infinite number of chemical compounds at very low concentrations .
The olfactory region consists of CILIA (Tiny, hair-like structures) projecting down out of the olfactory epithelium into a layer of mucous which is about 60 microns thick. This mucous layer is a fatty-rich secretion that bathes the receptors at the outer surface. The mucous layer is produced by special glands which are present in the olfactory epithelium. The mucous lipids (fats) assist in transporting the odorant molecules, as only volatile materials that are soluble in the mucous can interact with the smell receptors and initiate the signals that our brain interprets as smell. The olfactory cilia are the sites where molecular reception with the odorant occurs and sensory transmission starts.
For a long while it was thought that there are specific receptors for different odorant molecule and smell is initiated only when the right receptor is affected. An interesting feature of the physiology of smell was discovered by the 2004 Nobel Prize winners Linda Buck and Richard Axel. In contrast to the simple but specific key-lock model that governs taste, smell is dictated by a whole set of sensory cells. One type of fragrant molecule interacts with more than one receptor type, so the overall sensation is created by the combination of activated receptors and not a specific receptor as thought prior to their study.
Humans are able to distinguish between around 10,000 different odors. There are a combination of specific odor-sensing receptor cells that are capable of perceiving o it and the accumulation of the mixed information of these receptors pass the information of the “smell” of the specific odorant, on to the brain for their final disclosure. Although all people can identify most of the smells, some people trained as professionals “sniffers” in the fragrance/ cosmetics industry or professional food and wine tasters are considered to be in the high-end of this sensual ability they are more focused in distinguishing between the different odors and subsequently poses higher ability to describe the smell verbally, mainly by association.
Aroma refers to any volatized odor that reaches the olfactory bulb at the top of our nose. This odor can be sensed either through the nose or retro-nasally through the back of the mouth in the form of flavour. When the brain combines the taste stimuli with the aroma stimuli, flavor is perceived. (Tactile sensations such as the astringency from tannin or alcohol also play a role in flavour. Partially from: http://www.cf.ac.uk/biosi/staffinfo/jacob/teaching/sensory/olfact1.html#Tasteandsmell
Groups of Odors:
the Primary odor groups that appear in wine are: Fruity: ethyl acetate, Floral: flowers scent jasmine, roses, Spicy: ginger, pepper, Minty – Herbal: either from the mint family or fresh herbs, Resinous: resin, smoke, Burning: tar, toasted wood, Pungent: vinegar ,formic acid, acetic acid. There are Other Odor groups such as: Ethereal : Dry cleaning chemicals : Musky: muscone, Camphor – the smell of mothballs, eucalyptus oil, Rancid: smell of decomposition (isovaleric acid, butyric acid), Putrid: Foul rotten egg. Many esters have distinctive fruit-like odors, and many occur naturally in the essential oils of plants.
Ethyl acetate is the most common ester in wine, being the product of the most common volatile organic acid — acetic acid, and the ethyl alcohol generated during the fermentation. The aroma of ethyl acetate is most vivid in younger wines and contributes towards the general perception of “fruitiness” in the wine. Excessive amounts of ethyl acetate are considered a wine fault. Exposure to oxygen can exacerbate the fault due to the oxidation of ethanol to acetaldehyde, which leaves the wine with a sharp vinegar-like taste. (from Wikipedia)
Ester Name s and their Odors: Allyl hexanoate : pineapple, Benzyl acetate : pear, strawberry, jasmine, Bornyl acetate : pine, Butyl butyrate: pineapple, Ethyl acetate : nail polish remover, model airplane glue, Ethyl butyrate : banana, pineapple, strawberry, Ethyl hexanoate: waxy-green banana, Ethyl cinnamate : cinnamon, Ethyl formate: lemon, rum, strawberry, Ethyl heptanoate : apricot, cherry, grape, raspberry, Ethyl isovalerate: apple, Ethyl lactate: butter, cream, Ethyl nonanoate: grape, Ethyl pentanoate: apple, Geranyl acetate: geranium, Geranyl butyrate: cherry, Isobutyl acetate: cherry, raspberry, strawberry, Isobutyl formate: raspberry, Isoamyl acetate: pear, banana, Isopropyl acetate: fruity, Linalyl acetate: lavender, sage, Linalyl butyrate: peach, Linalyl formate: apple, peach, Methyl anthranilate: grape, jasmine, Methyl cinnamate: strawberry, Methyl pentanoate (methyl valerate): flowery, Octyl acetate: fruity-citrus, Pentyl butyrate (amyl butyrate): apricot, pear, pineapple, Propyl hexanoate: blackberry, pineapple, cheese, wine.
The sense of smell (or olfaction) is our most primitive sense. Scent messages pass directly through the limbic system (the emotional center of the brain), on its way to a conscious identification in the cortex. The Limbic system, supports a variety of functions, including emotion, behavior, creativity, motivation, long-term memory, and olfaction. It appears to be primarily responsible for our emotional life, and has a great deal to do with the formation of memories.
Since wine only very rarely possesses the tastes of the juice of the grape it is made of, Professional wine tasters use associations and analogies to everyday materials to describe aromas. Wine tasters Experts practice and use their sense of smell very frequently and they in fact “train” their sense of smell to improve, by methodical exposure to specific smells of a known origin. Accumulation of memories from known smells increases the smell vocabulary to a point that wine taste will “provoke” an association to other memorized smells from the Brain’s library of thousands of smells.
The sense of smell is one of the few senses that can be improved by training. It is possible to train our nose (and brain) to distinguish better, between smells. This can be achieved by sniffing something with a strong odor for a period several times a day. If we add new odors at set intervals continually for some time, our “vocabulary” of different odors will increase and we will be able through learning and memory to distinguish between larger arrays of the 10,000 or so existing odors. Our sense of smell, will also get stronger and association to known odors emitting materials will get faster.
People list smells which “make them happy. These are all part of their top 20 smell vocabulary: Freshly baked bread, Clean sheets, Freshly mown grass, Fresh flowers, Freshly ground coffee, Fresh air after rain fall, Vanilla, Chocolate, Fish & Chips, Bacon frying, Roast Dinner, Babies, Lemon zest, Lavender, Petrol, Apple and blackberry crumble in the oven, A freshly lit match, Roses, Party poppers, Rubber tyres. Apparently smell emotion and memory are interrelated in the brain as they originate in the same Limbic system
Next post on the specific scents of wine… soon.