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The aromas of wine are more diverse than its flavours. The human tongue is limited to the primary tastes perceived by taste receptors on the tongue –
sourness The gustatory system or sense of taste is the sensory system that is partially responsible for the perception of taste. Taste is the perception stimulated when a substance in the mouth reacts chemically with taste receptor cells located on t ...
, bitterness,
saltiness The gustatory system or sense of taste is the sensory system that is partially responsible for the perception of taste. Taste is the perception stimulated when a substance in the mouth biochemistry, reacts chemically with taste receptor cells l ...
,
sweetness Sweetness is a basic taste most commonly perceived when eating foods rich in sugars. Sweet tastes are generally regarded as pleasurable. In addition to sugars like sucrose, many other chemical compounds are sweet, including aldehydes, ketones ...
and savouriness. The wide array of fruit, earthy, leathery, floral, herbal, mineral, and woodsy flavour present in wine are derived from aroma notes sensed by the
olfactory bulb The olfactory bulb (Latin: ''bulbus olfactorius'') is a neural structure of the vertebrate forebrain involved in olfaction, the sense of smell. It sends olfactory information to be further processed in the amygdala, the orbitofrontal cortex (OF ...
.J. Robinson (ed) ''"The Oxford Companion to Wine"'' Third Edition p. 683 Oxford University Press 2006 In wine tasting, wine is sometimes smelled before taking a sip in order to identify some components of the wine that may be present. Different terms are used to describe what is being smelled. The most basic term is aroma which generally refers to a "pleasant" smell as opposed to odour which refers to an unpleasant smell or possible
wine fault A wine fault is a sensory-associated (organoleptic) characteristic of a wine that is unpleasant, and may include elements of taste, smell, or appearance, elements that may arise from a "chemical or a microbial origin", where particular sensory expe ...
. The term aroma may be further distinguished from bouquet which generally refers to the smells that arise from the chemical reactions of
fermentation Fermentation is a type of anaerobic metabolism which harnesses the redox potential of the reactants to make adenosine triphosphate (ATP) and organic end products. Organic molecules, such as glucose or other sugars, are catabolized and reduce ...
and aging of the wine.J. Robinson (ed) ''"The Oxford Companion to Wine"'' Third Edition p. 35 Oxford University Press 2006


Aroma vs. bouquet

In professional wine tasting, there is generally a distinction made between "aromas" and a wine's "bouquet" while in casual wine tasting these two terms are used interchangeably. An aroma refers to the smells unique to the
grape variety This list of grape varieties includes cultivated grapes, whether used for wine, or eating as a table grape, fresh or dried (raisin, Zante currant, currant, sultana (grape), sultana). For a complete list of all grape species, including those unimp ...
and are most readily demonstrated in a varietal wine – such as lychees with Gewürztraminer or black currant with Cabernet Sauvignon. These are smells that are commonly associated with a young wine. As a wine ages, chemical reactions among acids, sugars, alcohols and phenolic compounds create new smells that are known as a wine's bouquet. These can include
honey Honey is a sweet and viscous substance made by several species of bees, the best-known of which are honey bees. Honey is made and stored to nourish bee colonies. Bees produce honey by gathering and then refining the sugary secretions of pl ...
in an aged Sauternes or truffles in a
Pinot noir Pinot noir (), also known as Pinot nero, is a red-wine grape variety of the species ''Vitis vinifera''. The name also refers to wines created predominantly from Pinot noir grapes. The name is derived from the French language, French words fo ...
. The term bouquet can also be expanded to include the smells derived from fermentation and exposure to oak. In Burgundy, the aromas of wines are sub-divided into three categories – primary, secondary and tertiary aromas. Primary aromas are those specific to the grape variety itself. Secondary aromas are those derived from fermentation. Tertiary aromas are those that develop through either bottle or oak aging. The technique of microoxygenation affects the aromatic bouquet.


Components of a wine's aroma

Within wine there are volatile and non-volatile compounds that contribute to the make up of a wine's aroma. During the fermentation and for the first few months of a wine's existence, chemical reactions among these compounds occur frequently and a wine's aroma will change more rapidly during this period than at any other point. As a wine ages and matures, changes and developments in aroma will continue to take place but at a slower and more gradual pace. Volatile aroma compounds are present in the skin and juice of a grape berry and will vary in composition according to the individual grape variety. It is theorized that the ''
Vitis ''Vitis'' (grapevine) is a genus of 81 accepted species of vining plants in the flowering plant family Vitaceae. The genus consists of species predominantly from the Northern Hemisphere. It is economically important as the source of grapes, bot ...
'' vine developed these compounds as an
evolutionary Evolution is the change in the heritable characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, resulting in certa ...
tool to aid in procreation by attracting insects to assist with
pollination Pollination is the transfer of pollen from an anther of a plant to the stigma (botany), stigma of a plant, later enabling fertilisation and the production of seeds. Pollinating agents can be animals such as insects, for example bees, beetles or bu ...
and birds and other animals to eat the berries and disperse the seeds. The diverse spectrum of aromas associated with individual grape varieties is a reflection of the vine's adaptation to ecological conditions and competition among other plants.J. Robinson (ed) ''"The Oxford Companion to Wine"'' Third Edition pp. 273–274 Oxford University Press 2006 The majority of volatile compounds responsible for aroma combine with sugars in the wine to form odourless
glycosides In chemistry, a glycoside is a molecule in which a sugar is bound to another functional group via a glycosidic bond. Glycosides play numerous important roles in living organisms. Many plants store chemicals in the form of inactive glycosides. ...
. Through the process of
hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...
, caused by
enzymes An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as pro ...
or acids in the wine, they revert to an aromatic form. The act of tasting wine is essentially the act of smelling these vaporized aroma compounds.
Olfactory receptors Olfactory receptors (ORs), also known as odorant receptors, are chemoreceptors expressed in the cell membranes of olfactory receptor neurons and are responsible for the detection of odorants (for example, compounds that have an odor) which give ...
cells, each sensitive to a different aroma, pick up these compounds and transfer the information to the brain by way of the olfactory bulb.K. MacNeil ''The Wine Bible'' pp. 100–104 Workman Publishing 2001 In the 1980s there was renewed focus in studying the correlation between aroma/flavor compounds in grapes and the resulting quality of wine. Scientists were able to use chromatograph – mass spectrometers to identify volatile aroma compounds in various grape varieties. Study of the compounds responsible for aroma and flavour, as well as their correlation with a wine's quality, continues. As understanding of these compounds grows, there is concern that wines in the future could be "manipulated" through the use of chemical additives to add complexity and additional aromas to wine (such as creating a manufactured
perfume Perfume (, ) is a mixture of fragrance, fragrant essential oils or aroma compounds (fragrances), Fixative (perfumery), fixatives and solvents, usually in liquid form, used to give the human body, animals, food, objects, and living-spaces an agre ...
). In 2004, a winery in
South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...
was found to have added illegal flavouring to their Sauvignon blanc to enhance the aroma. Viticultural studies have focused on how aroma compounds develop in the grapes during the annual growth cycle of the vine and how viticultural techniques such as canopy management may contribute to developing desirable aromatics in the wine.


Identified aroma compounds

Some of the identified aroma compounds include the following: * Methoxypyrazine – grassy, herbaceous aroma compound associated with Cabernet Sauvignon and Sauvignon blanc. * Monoterpenes – responsible for the floral aromatics of varieties like Gewürztraminer, Muscat and Riesling. Includes geraniol, linalool and nerol. * Norisoprenoids – Carotenoid derived aromatic compoundsCarotenoid breakdown products the – norisoprenoids – in wine aroma. Maria Manuela Mendes-Pinto, Archives of Biochemistry and Biophysics, 15 March 2009, Volume 483, Issue 2, pp. 236–245, that includes megastigmatrienone which produces some of the spice notes associated with Chardonnay and zingerone responsible for the different spice notes associated with
Syrah Syrah (), also known as Shiraz, is a dark-skinned grape variety grown throughout the world and used primarily to produce red wine. In 1999, Syrah was found to be the offspring of two obscure grapes from southeastern France, Dureza and Mondeuse ...
. Other norisoprenoids include raspberry ketone which produces some of the
raspberry The raspberry is the edible fruit of several plant species in the genus ''Rubus'' of the Rosaceae, rose family, most of which are in the subgenus ''Rubus#Modern classification, Idaeobatus''. The name also applies to these plants themselves. Ras ...
aromas associated with red wine, damascenone which produces some of the rose oil aromas associated with
Pinot noir Pinot noir (), also known as Pinot nero, is a red-wine grape variety of the species ''Vitis vinifera''. The name also refers to wines created predominantly from Pinot noir grapes. The name is derived from the French language, French words fo ...
, and vanillin. * Thiols/ mercaptans –
sulfur Sulfur ( American spelling and the preferred IUPAC name) or sulphur ( Commonwealth spelling) is a chemical element; it has symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms ...
-containing compounds that can produce an aroma of garlic and
onion An onion (''Allium cepa'' , from Latin ), also known as the bulb onion or common onion, is a vegetable that is the most widely cultivated species of the genus '' Allium''. The shallot is a botanical variety of the onion which was classifie ...
that is considered a
wine fault A wine fault is a sensory-associated (organoleptic) characteristic of a wine that is unpleasant, and may include elements of taste, smell, or appearance, elements that may arise from a "chemical or a microbial origin", where particular sensory expe ...
. They have also been found to contribute to some of the varietal aromas associated with Cabernet Sauvignon, Gewürztraminer, Merlot, Muscat, Petit Manseng, Pinot blanc, Pinot gris, Riesling, Scheurebe, Semillon and Sylvaner.


Esters

Some of the aromas perceived in wine are from
ester In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...
s created by the reaction of organic acids and alcohols in the wine. Esters can develop during fermentation, with the influence of
yeast Yeasts are eukaryotic, single-celled microorganisms classified as members of the fungus kingdom (biology), kingdom. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are est ...
, or later during aging by a chemical reaction called esterification. The precise yeast strain used during fermentation and temperature are two of the strongest indicators of what kind of esters will develop and helps explain partially why Chardonnay grown in the same vineyard but made by two different producers could have different aromatics. During bottle aging
hydrogen Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
ions, found in higher concentration in low pH (high acid) wines, serves as a catalyst in the formation of esters from carboxylic acids and alcohols present in the wine. However, at the same time these hydrogen ions encourage esters to also split apart back into acids and alcohols. This creates many different types of carboxylic acids and alcohols at different times in the wines evolution which are then able to recombine with a different acid or alcohol. Each unique combination of alcohol and carboxylic acid produces a unique ester. During this period the ester influenced bouquet of the wine is dynamic and constantly changing. This is partly the reason why a wine will have one set of aromas at one time and other aromas later in its life.J. Robinson (ed) ''"The Oxford Companion to Wine"'' Third Edition p. 258 Oxford University Press 2006


In wine tasting

The sense of smell and detecting the aromas in wine is the primary means through which wine is tasted and evaluated. Prior to tasting the wine, wine drinkers will often smell the wine in the glass.T. Stevenson ''"The Sotheby's Wine Encyclopedia"'' p. 10 Dorling Kindersley 2005 Large bowl glasses with tapered openings, some of which are specifically designed to enhance aromatics of different wines, can assist in capturing more aromatics within the glass for the drinker to detect. Wines served at warmer temperature will be more aromatic than wine served cooler due to heat's ability to increase the volatility of aromatic compounds in the wine. Swirling, or aerating, the wine will increase available surface area, increasing the rate at which aroma molecules volatilize. Some subtle aromatics can be overwhelmed by more dominant aromatics that arise after swirling, so most professional tasters will sniff the wine briefly first before swirling. The closer the nose is to the wine, even right inside the glass, the greater chances of aromatics being captured. A series of short, quick sniffs versus one long inhale will also maximize the likelihood of aromatics being detected. The human nose starts to "fatigue" after around six seconds and so a pause may be needed between sniffs. When wine is sipped, it is warmed in the mouth and mixes with saliva to vaporize the volatile aroma compounds. These compounds are then inhaled "retro-nasally" through the back of the mouth to where it is received by nearly five million nerve cells. The average human can be trained to distinguish thousands of smells but can usually only name a handful at a time when presented with many aromas. This phenomenon, known as the "tip of the nose phenomenon", is countered when a person is given a list of possible choices, through which they can often positively identify the aroma. Professional wine tasters will often mentally cycle through a list of potential aromas (and may use visual aids like the aroma wheel, developed by Ann C. Noble of
University of California, Davis The University of California, Davis (UC Davis, UCD, or Davis) is a Public university, public Land-grant university, land-grant research university in Davis, California, United States. It is the northernmost of the ten campuses of the University ...
) until one choice stands out and can be identified in the wine. Detecting an aroma is only part of wine tasting. The next step is to describe or communicate what that aroma is and it is in this step that the subjective nature of wine tasting appears. Different individuals have their own way of describing familiar scents and aromas based on their unique experiences. Furthermore, there are varying levels of sensitivity and recognition thresholds among humans of some aromatic compounds. This is why one taster may describe different aromas and flavours from another taster sampling the very same wine.


See also

* Speyer wine bottle


References

{{Wines Wine Wine tasting