![Smelling the wine](https://upload.wikimedia.org/wikipedia/commons/0/07/Smelling_the_wine.jpg)
The aromas of wine are more diverse than its flavours. The
human tongue
The tongue is a muscular organ in the mouth of a typical tetrapod. It manipulates food for mastication and swallowing as part of the digestive process, and is the primary organ of taste. The tongue's upper surface (dorsum) is covered by taste bu ...
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 (flavor). Taste is the perception produced or stimulated when a substance in the mouth reacts chemically with taste recepto ...
,
bitterness,
saltiness
The gustatory system or sense of taste is the sensory system that is partially responsible for the perception of taste (flavor). Taste is the perception produced or stimulated when a substance in the mouth reacts chemically with taste receptor ...
,
sweetness 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 ( ...
.
[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 or defect is an unpleasant characteristic of a wine often resulting from poor winemaking practices or storage conditions, and leading to wine spoilage. Many of the compounds that cause wine faults are already naturally present in wine ...
. The term aroma may be further distinguished from bouquet which generally refers to the smells that arise from the chemical reactions of
fermentation and
aging of the wine.
[J. Robinson (ed) ''"The Oxford Companion to Wine"'' Third Edition p. 35 Oxford University Press 2006 ]
Aroma vs. bouquet
![Litchi chinensis Luc Viatour](https://upload.wikimedia.org/wikipedia/commons/f/f4/Litchi_chinensis_Luc_Viatour.jpg)
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, currant, sultana). For a complete list of all grape species including those unimportant to agriculture, see Viti ...
and are most readily demonstrated in a
varietal
A varietal wine is a wine made primarily from a single named grape variety, and which typically displays the name of that variety on the wine label.The American Heritage Dictionary of the English Language, Fourth Edition, 2000.winepros.com.au. ...
wine – such as
lychee
Lychee (US: ; UK: ; ''Litchi chinensis''; ) is a monotypic taxon and the sole member in the genus ''Litchi'' in the soapberry family, ''Sapindaceae''.
It is a tropical tree native to Southeast and Southwest China (the Guangdong, Fujian, Yun ...
s with
Gewürztraminer
Gewürztraminer () is an aromatic wine grape variety, used in white wines, and performs best in cooler climates. In English, it is sometimes referred to colloquially as Gewürz (; although this is never the case in German, because "Gewürz" me ...
or
black currant
The blackcurrant (''Ribes nigrum''), also known as black currant or cassis, is a deciduous shrub in the family Grossulariaceae grown for its edible berry, berries. It is native species, native to temperate climate, temperate parts of central ...
with
Cabernet Sauvignon. These are smells that are commonly associated with a young wine. As a wine ages, chemical reactions among
acids
In computer science, ACID ( atomicity, consistency, isolation, durability) is a set of properties of database transactions intended to guarantee data validity despite errors, power failures, and other mishaps. In the context of databases, a ...
,
sugars
Sugar is the generic name for sweet-tasting, soluble carbohydrates, many of which are used in food. Simple sugars, also called monosaccharides, include glucose, fructose, and galactose. Compound sugars, also called disaccharides or double ...
,
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 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 plants (primar ...
in an aged
Sauternes or
truffles
A truffle is the fruiting body of a subterranean ascomycete fungus, predominantly one of the many species of the genus ''Tuber''. In addition to ''Tuber'', many other genera of fungi are classified as truffles including '' Geopora'', '' Pe ...
in a
Pinot noir. The term bouquet can also be expanded to include the smells derived from fermentation and exposure to
oak
An oak is a tree or shrub in the genus ''Quercus'' (; Latin "oak tree") of the beech family, Fagaceae. There are approximately 500 extant species of oaks. The common name "oak" also appears in the names of species in related genera, notably ''L ...
. 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 Micro-oxygenation is a process used in winemaking to introduce oxygen into wine in a controlled manner. Developed in 1991 by Patrick DuCournau, working with the exceptionally tannic grape Tannat in Madiran, the process gained usage in modern win ...
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 79 accepted species of vining plants in the flowering plant family Vitaceae. The genus is made up of species predominantly from the Northern Hemisphere. It is economically important as the source of grapes, ...
'' vine developed these compounds as an
evolutionary
Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
tool to aid in
procreation
Reproduction (or procreation or breeding) is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or parents. Reproduction is a fundamental feature of all known life; each individual org ...
by attracting insects to assist with
pollination
Pollination is the transfer of pollen from an anther of a plant to the stigma of a plant, later enabling fertilisation and the production of seeds, most often by an animal or by wind. Pollinating agents can be animals such as insects, birds, a ...
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 ]
![Bee and grape cluster](https://upload.wikimedia.org/wikipedia/commons/d/d7/Bee_and_grape_cluster.jpg)
The majority of volatile compounds responsible for aroma combine with
sugars in the wine to form odourless
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, elimination, and solvation reactions in which water is the nucleophile.
Biological hydrolys ...
, caused by
enzymes or
acids in the wine, they revert to an aromatic form. The act of tasting wine is essentially the act of smelling these
vaporized
Vaporization (or vaporisation) of an element or compound is a phase transition from the liquid phase to vapor. There are two types of vaporization: evaporation and boiling. Evaporation is a surface phenomenon, whereas boiling is a bulk phenom ...
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 ri ...
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
In chemical analysis, chromatography is a laboratory technique for the separation of a mixture into its components. The mixture is dissolved in a fluid solvent (gas or liquid) called the ''mobile phase'', which carries it through a system (a ...
–
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 (, ; french: parfum) is a mixture of fragrant essential oils or aroma compounds (fragrances), fixatives and solvents, usually in liquid form, used to give the human body, animals, food, objects, and living-spaces an agreeable scent. Th ...
). In 2004, a winery in
South Africa
South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bounded to the south by of coastline that stretch along the Atlantic Ocean, South Atlantic and Indian Oceans; to the ...
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
In viticulture, the canopy of a grapevine includes the parts of the vine visible aboveground - the trunk, cordon, stems, leaves, flowers, and fruit. The canopy plays a key role in light energy capture via photosynthesis, water use as regulated ...
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
Muscat ( ar, مَسْقَط, ) is the capital and most populated city in Oman. It is the seat of the Governorate of Muscat. According to the National Centre for Statistics and Information (NCSI), the total population of Muscat Governorate was ...
and
Riesling
Riesling (, ; ) is a white grape variety that originated in the Rhine region. Riesling is an aromatic grape variety displaying flowery, almost perfumed, aromas as well as high acidity. It is used to make dry, semi-sweet, sweet, and sparkling wh ...
. Includes
geraniol
Geraniol is a monoterpenoid and an alcohol. It is the primary component of citronella oil and is a primary component of rose oil, palmarosa oil. It is a colorless oil, although commercial samples can appear yellow. It has low solubility in w ...
,
linalool
Linalool () refers to two enantiomers of a naturally occurring terpene alcohol found in many flowers and spice plants. Linalool has multiple commercial applications, the majority of which are based on its pleasant scent (floral, with a touch of ...
and
nerol
Nerol is a monoterpenoid alcohol found in many essential oils such as lemongrass and hops. It was originally isolated from neroli oil, hence its name. This colourless liquid is used in perfumery. Like geraniol, nerol has a sweet rose odor but it ...
.
*
Norisoprenoids –
Carotenoid derived aromatic compounds
[Carotenoid 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
Zingerone, also called vanillylacetone, is a major flavor component of ginger, providing the sweet flavor of cooked ginger. Zingerone is a crystalline solid that is sparingly soluble in water and soluble in ether.
Zingerone is similar in chemica ...
responsible for the different spice notes associated with
Syrah. Other norisoprenoids include
raspberry ketone
Raspberry ketone is a natural phenolic compound that is the primary aroma compound of red raspberries.
Occurrence
Raspberry ketone occurs in a variety of fruits, including raspberries, cranberries, and blackberries. It is biosynthesized from co ...
which produces some of the
raspberry aromas associated with red wine,
damascenone
Damascenones are a series of closely related chemical compounds that are components of a variety of essential oils. The damascenones belong to a family of chemicals known as rose ketones, which also includes damascones and ionones. ''beta''-Dam ...
which produces some of the
rose oil
Rose oil (rose otto, attar of rose, attar of roses, or rose essence) is the essential oil extracted from the petals of various types of rose. ''Rose ottos'' are extracted through steam distillation, while ''rose absolutes'' are obtained through ...
aromas associated with
Pinot noir, and
vanillin
Vanillin is an organic compound with the molecular formula . It is a phenolic aldehyde. Its functional groups include aldehyde, hydroxyl, and ether. It is the primary component of the extract of the vanilla bean. Synthetic vanillin is now u ...
.
*
Thiols
In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl grou ...
/
Mercaptans –
sulfur-containing compounds that can produce an aroma of
garlic and
onion
An onion (''Allium cepa'' L., from Latin ''cepa'' meaning "onion"), 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 onio ...
that is considered a
wine fault
A wine fault or defect is an unpleasant characteristic of a wine often resulting from poor winemaking practices or storage conditions, and leading to wine spoilage. Many of the compounds that cause wine faults are already naturally present in wine ...
. They have also been found to contribute to some of the varietal aromas associated with Cabernet Sauvignon, Gewürztraminer,
Merlot, Muscat,
Petit Manseng
Petit Manseng (sometimes translated: Small Manseng, rarely "Little Manseng") is a white wine grape variety that is grown primarily in South West France. It produces the highest quality wine of any grape in the Manseng family. The name is deriv ...
,
Pinot blanc
Pinot blanc is a white wine grape. It is a point genetic mutation of Pinot noir. Pinot noir is genetically unstable and will occasionally experience a point mutation in which a vine bears all black fruit except for one cane which produces white ...
,
Pinot gris
Pinot Gris, Pinot Grigio (, ) or Grauburgunder is a white wine grape variety of the species ''Vitis vinifera''. Thought to be a mutant clone of the Pinot Noir variety, it normally has a grayish-blue fruit, accounting for its name, but the gra ...
, Riesling,
Scheurebe
Scheurebe or Sämling 88 is a white wine grape variety. It is primarily grown in German wine, Germany and Austrian wine, Austria, where it often is called Sämling 88 (''English'': Seedling 88), and some parts of the New World. Scheurebe wines ar ...
,
Semillon and
Sylvaner.
Esters
Some of the aromas perceived in wine are from
ester
In chemistry, an ester is a compound derived from an oxoacid (organic or inorganic) in which at least one hydroxyl group () is replaced by an alkoxy group (), as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides a ...
s created by the reaction of acids and alcohol 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. The first yeast originated hundreds of millions of years ago, and at least 1,500 species are currently recognized. They are estimated to constit ...
, or later during aging by chemical reactions. 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 the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
ions, found in higher concentration in low
pH (high acid) wines, serves as a
catalyst
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
in the formation of esters from 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. These two counterbalancing acts gradually inch a wine closer to a state of
equilibrium where there is equal parts alcohol, acids, esters and water (a by product of the reactions). During this period the ester influenced bouquet of the wine is constantly changing due to the concentration, formulation and splitting of different esters. 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
Ann C. Noble is a Sensory analysis, sensory chemist and retired professor from the University of California, Davis. During her time at the UC Davis Department of Viticulture and Enology, Noble invented the "Aroma Wheel" which is credited with enha ...
, developed by
Ann C. Noble of
University of California, Davis
The University of California, Davis (UC Davis, UCD, or Davis) is a public land-grant research university near Davis, California. Named a Public Ivy, it is the northernmost of the ten campuses of the University of California system. The inst ...
) 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
The Speyer wine bottle (or ''Römerwein'') is a sealed vessel, presumed to contain liquid wine, and so named because it was unearthed from a Roman tomb found near Speyer, Germany. It is considered the world's oldest known bottle of wine.
Histor ...
References
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Wine
Wine tasting