Aroma of wine
Encyclopedia
Wine
Wine is an alcoholic beverage, made of fermented fruit juice, usually from grapes. The natural chemical balance of grapes lets them ferment without the addition of sugars, acids, enzymes, or other nutrients. Grape wine is produced by fermenting crushed grapes using various types of yeast. Yeast...
that wine is actually tasted
Wine tasting
Wine tasting is the sensory examination and evaluation of wine. While the practice of wine tasting is as ancient as its production, a more formalized methodology has slowly become established from the 14th century onwards...
. The human tongue is limited to the primary tastes perceived by taste receptors on the tongue-acidity, bitterness, saltiness, sweetness
Sweetness
Sweetness is one of the five basic tastes and is almost universally regarded as a pleasurable experience. Foods rich in simple carbohydrates such as sugar are those most commonly associated with sweetness, although there are other natural and artificial compounds that are sweet at much lower...
and umami
Umami
Umami , popularly referred to as savoriness, is one of the five basic tastes together with sweet, sour, bitter, and salty.-Etymology:Umami is a loanword from the Japanese meaning "pleasant savory taste". This particular writing was chosen by Professor Kikunae Ikeda from umai "delicious" and mi ...
. The wide array of fruit, earthy, floral, herbal, mineral and woodsy flavor perceived in wine are derived from aroma notes interpreted by the olfactory bulb
Olfactory bulb
The olfactory bulb is a structure of the vertebrate forebrain involved in olfaction, the perception of odors.-Anatomy:In most vertebrates, the olfactory bulb is the most rostral part of the brain. In humans, however, the olfactory bulb is on the inferior side of the brain...
. 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. The most basic term is aroma which generally refers to a "pleasant" smell as opposed to odor which refers to an unpleasant smell or possible wine fault
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 but at insufficient concentrations to adversely...
. The term aroma maybe further distinguished from bouquet which generally refers to the smells that arise from the chemical reactions of fermentation
Fermentation (wine)
The process of fermentation in wine turns grape juice into an alcoholic beverage. During fermentation, yeast interact with sugars in the juice to create ethanol, commonly known as ethyl alcohol, and carbon dioxide...
and aging of the wine.
Aroma vs bouquet
Varietal
"Varietal" describes wines made primarily from a single named grape variety, and which typically displays the name of that variety on the wine label. Examples of grape varieties commonly used in varietal wines are Cabernet Sauvignon, Chardonnay and Merlot...
wine--such as lychee
Lychee
The lychee is the sole member of the genus Litchi in the soapberry family, Sapindaceae. It is a tropical and subtropical fruit tree native to Southern China and Southeast Asia, and now cultivated in many parts of the world...
s with Gewürztraminer
Gewürztraminer
Gewürztraminer is an aromatic wine grape variety that performs best in cooler climates. It is sometimes referred to colloquially as Gewürz, and in French it is written '...
or black currant with Cabernet Sauvignon
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 Canada's Okanagan Valley to Lebanon's Beqaa Valley...
. 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
Honey is a sweet food made by bees using nectar from flowers. The variety produced by honey bees is the one most commonly referred to and is the type of honey collected by beekeepers and consumed by humans...
in an aged Sauternes
Sauternes (wine)
Sauternes is a French sweet wine from the Sauternais region of the Graves section in Bordeaux. Sauternes is made from Sémillon, Sauvignon Blanc, and Muscadelle grapes that have been affected by Botrytis cinerea, also known as noble rot. This causes the grapes to become partially raisined,...
or truffles in a Pinot noir
Pinot Noir
Pinot noir is a black wine grape variety of the species Vitis vinifera. The name may also refer to wines created predominantly from Pinot noir grapes...
. 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 and oak aging. Tertiary aromas are those that develop through bottled aging.
Components of a wine's aroma
Within wine there are volatileVolatility (chemistry)
In chemistry and physics, volatility is the tendency of a substance to vaporize. Volatility is directly related to a substance's vapor pressure. At a given temperature, a substance with higher vapor pressure vaporizes more readily than a substance with a lower vapor pressure.The term is primarily...
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
Vitis is a genus of about 60 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, both for direct consumption of the fruit and for fermentation to produce...
vine developed these compounds as a evolutionary tool to aid in procreation by attracting insects to assist with pollination
Pollination
Pollination is the process by which pollen is transferred in plants, thereby enabling fertilisation and sexual reproduction. Pollen grains transport the male gametes to where the female gamete are contained within the carpel; in gymnosperms the pollen is directly applied to the ovule itself...
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.
Hydrolysis
Hydrolysis is a chemical reaction during which molecules of water are split into hydrogen cations and hydroxide anions in the process of a chemical mechanism. It is the type of reaction that is used to break down certain polymers, especially those made by condensation polymerization...
, caused by enzymes or acids in the wine, they revert into an aromatic form. The act of tasting wine is essentially the act of smelling these vaporized aroma compounds. Olfactory receptors cells, each sensitive to a different aromas, pick up these compounds and transfers the information to the brain by way of the olfactory bulb. 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
Mass spectrometry is an analytical technique that measures the mass-to-charge ratio of charged particles.It is used for determining masses of particles, for determining the elemental composition of a sample or molecule, and for elucidating the chemical structures of molecules, such as peptides and...
to identify volatile aroma compounds in various grape varieties.
Study of the compounds responsible for aroma and flavor, as well as their correlation with a wine's quality, is ongoing. 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
Perfume is a mixture of fragrant essential oils and/or aroma compounds, fixatives, and solvents used to give the human body, animals, objects, and living spaces "a pleasant scent"...
) . In 2004, a winery in South Africa was found to have added illegal flavoring to their Sauvignon blanc
Sauvignon blanc
Sauvignon Blanc is a green-skinned grape variety which originates from the Bordeaux region of France. The grape most likely gets its name from the French word sauvage and blanc due to its early origins as an indigenous grape in South West France., a possible descendant of savagnin...
to enhance the aroma. Viticultural studies
Viticulture
Viticulture is the science, production and study of grapes which deals with the series of events that occur in the vineyard. When the grapes are used for winemaking, it is also known as viniculture...
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 RieslingRieslingRiesling is a white grape variety which originated in the Rhine region of Germany. 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 white wines. Riesling wines are usually varietally...
. Includes geraniolGeraniolGeraniol is a monoterpenoid and an alcohol. It is the primary part of rose oil, palmarosa oil, and citronella oil . It also occurs in small quantities in geranium, lemon, and many other essential oils. It appears as a clear to pale-yellow oil that is insoluble in water, but soluble in most common...
, linalool and nerolNerolNerol is a monoterpene 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 is considered to be fresher.Isomeric with nerol is geraniol,...
. - Norisoprenoids-CarotenoidCarotenoidCarotenoids are tetraterpenoid organic pigments that are naturally occurring in the chloroplasts and chromoplasts of plants and some other photosynthetic organisms like algae, some bacteria, and some types of fungus. Carotenoids can be synthesized fats and other basic organic metabolic building...
derived aromatic compound that includes megastigmatrienone which produces some of the spice notes associated with ChardonnayChardonnayChardonnay is a green-skinned grape variety used to make white wine. It is originated from the Burgundy wine region of eastern France but is now grown wherever wine is produced, from England to New Zealand...
and zingeroneZingeroneZingerone, also called vanillylacetone, is a key component of the pungency of ginger. Zingerone is a crystalline solid that is sparingly soluble in water, but soluble in ether....
responsible for the different spice notes associated with Syrah. Other norisoprenoids include raspberry ketoneRaspberry ketoneRaspberry ketone is a natural phenolic compound that is the primary aroma compound of red raspberries. It is used in perfumery, in cosmetics, and as a food additive to impart a fruity odor. It is one of the most expensive natural flavor components used in the food industry. The natural compound...
which produces some of the raspberryRaspberryThe raspberry or hindberry is the edible fruit of a multitude of plant species in the genus Rubus, most of which are in the subgenus Idaeobatus; the name also applies to these plants themselves...
aromas associated with red wine, damascenoneDamascenoneDamascenones 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...
which produces some of the rose oilRose oilRose oil, meaning either rose otto or rose absolute, is the essential oil extracted from the petals of various types of rose...
aromas associated with Pinot noirPinot NoirPinot noir is a black wine grape variety of the species Vitis vinifera. The name may also refer to wines created predominantly from Pinot noir grapes...
and vanillinVanillinVanillin is a phenolic aldehyde, an organic compound with the molecular formula C8H8O3. Its functional groups include aldehyde, ether, and phenol. It is the primary component of the extract of the vanilla bean. It is also found in Leptotes bicolor, roasted coffee and the Chinese red pine...
. - Thiols-sulfurSulfurSulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
contain compounds that can produce an aroma of garlicGarlicAllium sativum, commonly known as garlic, is a species in the onion genus, Allium. Its close relatives include the onion, shallot, leek, chive, and rakkyo. Dating back over 6,000 years, garlic is native to central Asia, and has long been a staple in the Mediterranean region, as well as a frequent...
and onionOnionThe onion , also known as the bulb onion, common onion and garden onion, is the most widely cultivated species of the genus Allium. The genus Allium also contains a number of other species variously referred to as onions and cultivated for food, such as the Japanese bunching onion The onion...
that is considered a wine faultWine faultA 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 but at insufficient concentrations to adversely...
(mercaptans). They have also been found to contribute to some of the varietal aromas associated with Cabernet Sauvignon, Gewürztraminer, MerlotMerlotMerlot is a darkly blue-coloured wine grape, that is used as both a blending grape and for varietal wines. The name Merlot is thought to derive from the Old French word for young blackbird, merlot, a diminutive of merle, the blackbird , probably from the color of the grape. Merlot-based wines...
, Muscat, Petit MansengPetit MansengPetit 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 derived from its small, thick skin berries. Coupled with the small yields of the grapevine, most Petit Manseng farmers...
, Pinot blancPinot BlancPinot 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 produced white fruit....
, Pinot grisPinot grisPinot gris is a white wine grape variety of the species Vitis vinifera. Thought to be a mutant clone of the Pinot noir grape, it normally has a grayish-blue fruit, accounting for its name but the grape can have a brownish pink to black and even white appearance...
, Riesling, ScheurebeScheurebeScheurebe or Sämling 88 is a white wine grape variety. It is primarily grown in Germany and Austria, where it often is called Sämling 88 , and some parts of the New World...
, SemillonSémillonSémillon is a golden-skinned grape used to make dry and sweet white wines, most notably in France and Australia.-History:The origin of the Sémillon grape is hard to determine. It is known that it first arrived in Australia in the early 19th century and by the 1820s the grape covered over 90 percent...
and Sylvaner.
Esters
Some of the aromas perceived in wine are from esterEster
Esters are chemical compounds derived by reacting an oxoacid with a hydroxyl compound such as an alcohol or phenol. Esters are usually derived from an inorganic acid or organic acid in which at least one -OH group is replaced by an -O-alkyl group, and most commonly from carboxylic acids and...
s created by the reaction of acids and alcohol in the wine. Esters can develop during fermentation, with the influence of yeast
Yeast
Yeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with 1,500 species currently described estimated to be only 1% of all fungal species. Most reproduce asexually by mitosis, and many do so by an asymmetric division process called budding...
, 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
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
ions, found in higher concentration in low pH
PH
In chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
(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 counter-balancing 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.
In wine tasting
When wine is sipped, it is warmed in the mouth and mixes with saliva
Saliva
Saliva , referred to in various contexts as spit, spittle, drivel, drool, or slobber, is the watery substance produced in the mouths of humans and most other animals. Saliva is a component of oral fluid. In mammals, saliva is produced in and secreted from the three pairs of major salivary glands,...
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
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 understanding of wine tasting and terminology...
of University of California, Davis
University of California, Davis
The University of California, Davis is a public teaching and research university established in 1905 and located in Davis, California, USA. Spanning over , the campus is the largest within the University of California system and third largest by enrollment...
) 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 flavors from another taster sampling the very same wine.