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 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 ...

perceived by taste receptors on the tongue – sourness, bitterness, saltiness,

sweetness Sweetness is a Taste#Basic tastes, basic taste most commonly Perception, perceived when eating foods rich in sugars. Sweet tastes are generally regarded as pleasure, pleasurable. In addition to sugars like sucrose, many other chemical compounds ...

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.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. 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 metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food ...

and

aging of the wine The aging of wine is potentially able to improve the quality of wine. This distinguishes wine from most other consumable goods. While wine is perishable and capable of deteriorating, complex chemical reactions involving a wine's sugars, acids and ...

.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 and are most readily demonstrated in a varietal wine – such as lychees with Gewürztraminer or black currant with

Cabernet Sauvignon Cabernet Sauvignon () is one of the world's most widely recognized red wine grape varieties. It is grown in nearly every major wine producing country among a diverse spectrum of climates from Australia and British Columbia, Canada to Lebanon' ...

. These are smells that are commonly associated with a young wine. As a wine ages, chemical reactions among acids, sugars,

alcohols In chemistry, an alcohol is a type of organic compound that carries at least one hydroxyl () functional group bound to a saturated carbon atom. The term ''alcohol'' originally referred to the primary alcohol ethanol (ethyl alcohol), which is ...

and

phenolic compounds In organic chemistry, phenols, sometimes called phenolics, are a class of chemical compounds consisting of one or more hydroxyl groups (— O H) bonded directly to an aromatic hydrocarbon group. The simplest is phenol, . Phenolic compounds are c ...

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'', ''Peziza ...

in a

Pinot noir Pinot Noir () is a red-wine grape variety of the species ''Vitis vinifera''. The name may also refer to wines created predominantly from pinot noir grapes. The name is derived from the French language, French words for ''pine'' and ''black.' ...

. 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'' vine developed these compounds as an evolutionary tool to aid in procreation by attracting insects to assist with pollination 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

The majority of volatile compounds responsible for aroma combine with

sugars in the wine Sugars in wine are at the heart of what makes winemaking possible. During the process of fermentation, sugars from wine grapes are broken down and converted by yeast into alcohol (ethanol) and carbon dioxide. Grapes accumulate sugars as they grow ...

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, caused by

enzymes Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different molecule ...

acids in the wine The acids in wine are an important component in both winemaking and the finished product of wine. They are present in both grapes and wine, having direct influences on the color, balance and taste of the wine as well as the growth and vitality of ...

, 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 phenomenon. ...

aroma compounds. Olfactory receptors 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 Mass spectrometry (MS) is an analytical technique that is used to measure the mass-to-charge ratio of ions. The results are presented as a ''mass spectrum'', a plot of intensity as a function of the mass-to-charge ratio. Mass spectrometry is used ...

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). In 2004, a winery in South Africa was found to have added illegal flavouring to their

Sauvignon blanc is a green-skinned grape variety that originates from the Bordeaux region of France. The grape most likely gets its name from the French words ''sauvage'' ("wild") and ''blanc'' ("white") due to its early origins as an indigenous grape in ...

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 Methoxypyrazines are a class of chemical compounds that produce odors. The odors tend to be undesirable, as in the case of certain wines, or as defensive chemicals used by insects such as ''Harmonia axyridis'' which produces isopropyl methoxy pyra ...

– grassy, herbaceous aroma compound associated with Cabernet Sauvignon and Sauvignon blanc. *

Monoterpenes Monoterpenes are a class of terpenes that consist of two isoprene units and have the molecular formula C10H16. Monoterpenes may be linear (acyclic) or contain rings (monocyclic and bicyclic). Modified terpenes, such as those containing oxygen funct ...

– responsible for the floral aromatics of varieties like Gewürztraminer, Muscat and Riesling. Includes geraniol, linalool and nerol. *

Norisoprenoids Terpenes () are a class of natural products consisting of compounds with the formula (C5H8)n for n > 1. Comprising more than 30,000 compounds, these unsaturated hydrocarbons are produced predominantly by plants, particularly conifers. Terpenes ar ...

–

Carotenoid Carotenoids (), also called tetraterpenoids, are yellow, orange, and red organic compound, organic pigments that are produced by plants and algae, as well as several bacteria, and Fungus, fungi. Carotenoids give the characteristic color to pumpki ...

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 ''Nicotiana tabacum'', or cultivated tobacco, is an annually grown herbaceous plant of the ''Nicotiana'' genus. The plant is tropical in origin, is commonly grown throughout the world, and is often found in cultivation. It grows to heights bet ...

which produces some of the spice notes associated with

Chardonnay Chardonnay (, , ) is a green-skinned grape variety used in the production of white wine. The variety originated in the Burgundy wine region of eastern French wine, France, but is now grown wherever wine is produced, from English wine, Englan ...

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 B ...

. Other norisoprenoids include

raspberry ketone Raspberry ketone is a natural phenolic compound that is the primary aroma compound of red raspberry, red raspberries. Occurrence Raspberry ketone occurs in a variety of fruits, including raspberries, cranberry, cranberries, and blackberry, blackb ...

which produces some of the

raspberry The raspberry is the edible fruit of a multitude of plant species in the genus ''Rubus'' of the rose family, most of which are in the subgenus '' Idaeobatus''. The name also applies to these plants themselves. Raspberries are perennial with w ...

aromas associated with red wine, damascenone which produces some of the rose oil aromas associated with

, and vanillin. * Thiols/

Mercaptans 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 gro ...

–

sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...

-containing compounds that can produce an aroma of

garlic Garlic (''Allium sativum'') is a species of bulbous flowering plant in the genus ''Allium''. Its close relatives include the onion, shallot, leek, chive, Allium fistulosum, Welsh onion and Allium chinense, Chinese onion. It is native to South A ...

and onion that is considered a wine fault. They have also been found to contribute to some of the varietal aromas associated with Cabernet Sauvignon, Gewürztraminer,

Merlot Merlot is a dark blue–colored wine grape variety, that is used as both a blending grape and for varietal wines. The name ''Merlot'' is thought to be a diminutive of ''merle'', the French name for the blackbird, probably a reference to the ...

, Muscat, Petit Manseng, Pinot blanc, Pinot gris, Riesling, Scheurebe, Semillon and

Sylvaner Sylvaner or Silvaner is a variety of white wine grape grown primarily in Alsace and Germany, where its official name is Grüner Silvaner. While the Alsatian versions have primarily been considered simpler wines, it was included among the vari ...

Esters

Some of the aromas perceived in wine are from esters created by the reaction of acids and alcohol in the wine. Esters can develop during fermentation, with the influence of yeast, 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 ions, found in higher concentration in low pH (high acid) wines, serves as a catalyst 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 Saliva (commonly referred to as spit) is an extracellular fluid produced and secreted by salivary glands in the mouth. In humans, saliva is around 99% water, plus electrolytes, mucus, white blood cells, epithelial cells (from which DNA can be ...

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 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 enhancing the public ...

, developed by

Ann C. Noble Ann C. Noble is a 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 enhancing the public ...

of University of California, Davis) 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.

References