Wine fault
Encyclopedia
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 affect it. In fact, depending on perception
, these concentrations may impart positive characters to the wine. However when the concentration of these compounds greatly exceeds the sensory threshold
, they replace or obscure the flavor
s and aromas that the wine should be expressing. Ultimately the quality of the wine is reduced, making it less appealing and sometimes undrinkable.
There are many causes for the perception in wine faults ranging from poor hygiene
at the winery, excessive and/or insufficient exposure of the wine to oxygen
, excessive or insufficient exposure of the wine to sulphur, overextended maceration
of the wine either pre or post fermentation
, faulty fining, filtering and stabilization of the wine, the use of dirty oak barrels, over extended barrel aging and the use of poor quality corks. Outside of the winery, other factors within the control of the retailer or end user of the wine can contribute to the perception of flaws in the wine. These include poor storage of the wine that exposes it to excessive heat and temperature fluctuations as well as the use of dirty stemware
during wine tasting
that can introduce materials or aromas to what was previously a clean and fault-free wine.
, volatile acidity, Brettanomyces
or "Brett aromas" and diacetyl
or buttery aromas. The amount to which these aromas or attributes become excessive is dependent on the particular tastes and recognition threshold of the wine taster. Generally, a wine exhibiting these qualities is still considered drinkable by the large masses. However, some flaws such as volatile acidity and Brettanomyces can be considered a fault when they are in such an excess that they overwhelm other components of the wine. Wine faults are generally major attributes that make a wine undrinkable to most wine tasters. Examples of wine faults include acetaldehyde
(except when purposely induced in wines like Sherry
and Rancio), ethyl acetate
and cork taint
.
or malolactic fermentation
happening in the bottle. Unusual breaks in the color of the wine could be a sign of excessive copper
, iron
or proteins that were not removed during fining or filtering. A wine with an unusual color for its variety or wine region could be a sign of excessive or insufficient maceration or as well as poor temperature controls during fermentation. Tactile clues of potential wine faults include the burning, acidic taste associated with volatile acidity that can make a wine seem out of balance.
and a catalyst are the only requirements for the process to occur. It is also known as maderized wine, from Madeira wine
, which is intentionally oxidized.
Oxidation can occur throughout the winemaking process, and even after the wine has been bottled. Anthocyanin
s, catechin
s, epicatechins and other phenols present in wine are those most easily oxidised , which leads to a loss of colour, flavour and aroma - sometimes referred to as flattening. In most cases compounds such as sulfur dioxide
or erythorbic acid
are added to wine by winemakers, which protect the wine from oxidation and also bind with some of the oxidation products to reduce their organoleptic effect. Apart from phenolic oxidation, the ethanol
present within wine can also be oxidised into other compounds responsible for flavour and aroma taints.
is an intermediate product of yeast fermentation
; however, it is more commonly associated with ethanol
oxidation catalysed by the enzyme ethanol dehydrogenase
. Acetaldehyde production is also associated with the presence of surface film forming yeasts and bacteria, such as acetic acid bacteria
, which form the compound by the decarboxylation
of pyruvate. The sensory threshold
for acetaldehyde is 100-125 mg/L
. Beyond this level it imparts a sherry
type character to the wine which can also be described as green apple, sour and metallic. Acetaldehyde intoxication is also implicated in hangover
s.
in wine, often referred to as volatile acidity (VA) or vinegar taint, can be contributed by many wine spoilage yeasts and bacteria
. This can be from either a by-product
of fermentation, or due to the spoilage of finished wine. Acetic acid bacteria, such as those from the genera Acetobacter
and Gluconobacter produce high levels of acetic acid. The sensory threshold
for acetic acid is >700 mg/L, with concentrations greater than 1.2-1.3 g/L becoming unpleasant.
There are different opinions as to what level of volatile acidity is appropriate for higher quality wine. Although too high a concentration is sure to leave an undesirable, 'vinegar' tasting wine, some wine's acetic acid levels are developed to create a more 'complex', desirable taste. The renowned 1947 Cheval Blanc
is widely recognized to contain high levels of volatile acidity.
Ethyl acetate
is formed in wine by the esterification of ethanol and acetic acid. Therefore wines with high acetic acid levels are more likely to see ethyl acetate formation, but the compound does not contribute to the volatile acidity. It is a common microbial fault produced by wine spoilage yeasts, particularly Pichia anomala, Kloeckera apiculata, and Hanseniaspora uvarum. High levels of ethyl acetate are also produced by lactic acid bacteria
and acetic acid bacteria
. The sensory threshold for ethyl acetate is 150–200 mg/L. Levels below this can give an added richness and sweetness, whereas levels above impart nail polish remover, glue
, or varnish
type aromas.
is used as an additive
throughout the winemaking process, primarily to stop oxidation as mentioned above but also as antimicrobial
agent. When managed properly in wine, its presence there is often undetected, however when used recklessly it can contribute to flavour and aroma taints which are very volatile and potent. Sulfur compounds typically have low sensory thresholds.
Sulfur dioxide
is a common wine additive, used for its antioxidant
and preservative
properties. When its use is not managed well it can be overadded, with its perception in wine reminiscent of matchsticks, burnt rubber, or mothballs. Wines such as these are often termed sulfitic.
Hydrogen sulfide
(H2S) is generally thought to be a metabolic by-product of yeast fermentation in nitrogen
limited environments. It is formed when yeast ferments via the sulfate reduction pathway. Fermenting wine is often supplemented with diammonium phosphate
(DAP) as a nitrogen source to prevent H2S formation. The sensory threshold for hydrogen sulfide is 8-10 μg/L, with levels above this imparting a distinct rotten egg aroma to the wine. Hydrogen sulfide can further react with wine compounds to form mercaptans and disulfide
s.
Mercaptans (thiols) are produced in wine by the reaction of hydrogen sulfide with other wine components such as ethanol or sulfur containing amino acids, such as methionine
. They can be formed if finished wine is allowed prolonged contact with the lees
. This can be prevented by racking
the wine. Mercaptans have a very low sensory threshold, around 1.5 µg/L
, with levels above causing onion, rubber, and skunk type odours.
Dimethyl sulfide
(DMS) is naturally present in most wines, probably from the breakdown of sulfur containing amino acids. Like ethyl acetate, levels of DMS below the sensory threshold can have a positive effect on flavour, contributing to fruityness, fullness, and complexity. Levels above the sensory threshold of >30 µg/L in white wines and >50 µg/L for red wines, give the wine characteristics of cooked cabbage, canned corn, asparagus or truffles. Note that dimethyl sulfide is not formed from the oxidation of mercaptans, but dimethyl disulfide
is.
Cork taint is a wine fault mostly attributed to the compound 2,4,6-trichloroanisole
(TCA), although other compounds such as guaiacol
, geosmin
, 2-methylisoborneol
, 1-octen-3-ol
, 1-octen-3-one, 2,3,4,6-tetrachloroanisole, pentachloroanisole, and 2,4,6-tribromoanisole
are also thought to be involved. TCA most likely originates as a metabolite
of mould growth on chlorine
-bleached wine corks and barrels. It causes earthy, mouldy, and musty aromas in wine that easily mask the natural fruit aromas, making the wine very unappealing. Wines in this state are often described as "corked". As cork taint has gained a wide reputation as a wine fault, other faults are often mistakenly attributed to it.
, and may even push up between the cork and bottle and leak from the top. When opening a bottle of wine, if a track of wine is visible along the length of the cork, the cork is partially pushed out of the bottle, or wine is visible on the top of the cork while it is still in the bottle, it has most likely been heat damaged. Heat damaged wines often become oxidized, and red wines may take on a brick color.
Even if the temperatures do not reach extremes, temperature variation alone can also damage bottled wine through oxidation. All corks allow some leakage of air (hence old wines become increasingly oxidized), and temperature fluctuations will vary the pressure differential between the inside and outside of the bottle and will act to "pump" air into the bottle at a faster rate than will occur at any temperature strictly maintained.
Reputedly, heat damage is the most widespread and common problem found in wines. It often goes unnoticed because of the prevalence of the problem, consumers don't know it's possible, and most often would just chalk the problem up to poor quality, or other factors.
light, particularly in the range 325 to 450 nm. Very delicate wines, such as Champagnes, are generally worst affected, with the fault causing a wet cardboard or wet wool type flavour and aroma. Red wines rarely become lightstruck because of the phenolic compounds present within the wine that protect it. Lightstrike is thought to be caused by sulfur compounds such as dimethyl sulfide
. In France lightstrike is known as "goût de lumière", which translates to a taste of light. The fault explains why wines are generally bottled in coloured glass, which blocks the ultraviolet light, and why wine should be stored in dark environments.
s, that are perceived as rancid peanut butter
, bitter herbaceous, green bell pepper
, or cat urine. This is also a naturally occurring compound in Sauvignon grapes and so ladybug taint has been known to make Riesling
s taste like Sauvignon Blanc
.
The yeast Brettanomyces
produces an array of metabolite
s when growing in wine, some of which are volatile phenolic compounds. Together these compounds are often referred to as "Brettanomyces character", or simply "Brett". The main constituents are listed below, with their sensory threshold and common sensory descriptors:
is a compound with a very distinct earthy, musty, beetroot, even turnip flavour and aroma and has an extremely low sensory threshold of down to 10 parts per trillion. Its presence in wine is usually derived as metabolite from the growth of filamentous actinomycetes
such as Streptomyces
, and mould
s such as Botrytis cinerea
and Penicillium expansum, on grapes. Wines affected by but not attributed to geosmins are often thought to have earthy properties due to terroir
. The geosmin fault occurs worldwide and has been found in recent vintages of red wines from Beaujolais
, Bordeaux
, Burgundy
and the Loire
in France. Geosmin is also thought to be a contributing factor in cork taint
.
have a useful role in winemaking converting malic acid to lactic acid in malolactic fermentation
. However after this function has completed the bacteria may still be present within the wine, where they can metabolise other compounds and produce wine faults. Wines that have not undergone malolactic fermentation may be contaminated with lactic acid bacteria, leading to refermentation of the wine with it becoming turbid
, swampy, and slightly effervescent
or spritzy. This can be avoided by sterile filtering wine directly before bottling. Lactic acid bacteria can also be responsible for other wine faults such as those below.
Bitterness taint or amertume is rather uncommon and is produced by certain strains of bacteria from the genera Pediococcus
, Lactobacillus
, and Oenococcus
. It begins by the degradation of glycerol
, a compound naturally found in wine at levels of 5-8 g/L, via a dehydratase
enzyme to 3-hydroxypropionaldehyde. During ageing this is further dehydrated to acrolein
which reacts with the anthocyanin
s and other phenols present within the wine to form the taint. As red wines contain high levels of anthocyanins they are generally more susceptible.
Diacetyl
in wine is produced by lactic acid bacteria
, mainly Oenococcus oeni
. In low levels it can impart positive nutty or caramel characters, however at levels above 5 mg/L it creates an intense buttery or butterscotch
flavour, where it is perceived as a flaw. The sensory threshold for the compound can vary depending on the levels of certain wine components, such as sulfur dioxide. It can be produced as a metabolite of citric acid
when all of the malic acid
has been consumed. Diacetyl rarely taints wine to levels where it becomes undrinkable.
Geranium taint, as the name suggests, is a flavour and aroma taint in wine reminiscent of geranium
leaves. The compound responsible is 2-ethoxyhexa-3,5-diene, which has a low sensory threshold concentration of 0.1 mg/L. In wine it is formed during the metabolism
of potassium sorbate
by lactic acid bacteria
. Potassium sorbate is sometimes added to wine as a preservative
against yeast, however its use is generally kept to a minimum due to the possibility of the taint developing. The production of the taint begins with the conversion of sorbic acid
to the alcohol sorbinol. The alcohol is then isomerised
in the presence of acid to 3,5-hexadiene-2-ol, which is then esterified with ethanol to form 2-ethoxy-3,5-hexadiene
.
Mannitol
is a sugar alcohol
, and in wine it is produced by heterofermentative lactic acid bacteria, such as Lactobacillus brevis
, by the reduction
of fructose
. Its perception is often complicated as it generally exists in wine alongside other faults, but it is usually described as viscous, ester
-like combined with a sweet and irritating finish. Mannitol is usually produced in wines that undergo malolactic fermentation with a high level of residual sugars still present.
and a slimey or fatty mouthfeel of a wine. In France the fault is known as "graisse", which translates to fat. The problem stems from the production of dextrin
s and polysaccharide
s by certain lactic acid bacteria, particularly of the genera Leuconostoc
and Pediococcus
.
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Mousiness is a wine fault most often attributed to Brettanomyces but can also originate from the lactic acid bacteria
Lactobacillus brevis
, Lactobacillus fermentum
, and Lactobacillus hilgardii, and hence can occur in malolactic fermentation
. The compounds responsible are lysine
derivatives, mainly;
The taints are not volatile at the pH
of wine, and therefore not obvious as an aroma. However, when mixed with the slightly basic pH of saliva they can become very apparent on the palate, especially at the back of the mouth, as mouse cage or mouse urine.
are bottled in non-sterile
conditions, allowing the presence of microorganisms. The most common yeast to referment wine is the standard wine fermentation yeast Saccharomyces cerevisiae
, but has also been attributed to Schizosaccharomyces pombe
and Zygosaccharomyces bailii
. The main issues associated with the fault include turbidity
(from yeast biomass
production), excess ethanol production (may violate labelling
laws), slight carbonation
, and some coarse odours. Refermentation can be prevented by bottling wines dry (with residual sugar levels <1.0g/L), sterile filtering wine prior to bottling, or adding preservative chemicals such as dimethyl dicarbonate
. The Portuguese wine
style known as "vinhos verdes
" relies on this
secondary fermentation in bottle to impart a slight spritziness to the wine.
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...
often resulting from poor winemaking
Winemaking
Winemaking, or vinification, is the production of wine, starting with selection of the grapes or other produce and ending with bottling the finished wine. Although most wine is made from grapes, it may also be made from other fruit or non-toxic plant material...
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 affect it. In fact, depending on perception
Perception
Perception is the process of attaining awareness or understanding of the environment by organizing and interpreting sensory information. All perception involves signals in the nervous system, which in turn result from physical stimulation of the sense organs...
, these concentrations may impart positive characters to the wine. However when the concentration of these compounds greatly exceeds the sensory threshold
Sensory threshold
Sensory threshold is a theoretical concept used in psychophysics. A stimulus that is less intense than the sensory threshold will not elicit any sensation...
, they replace or obscure the flavor
Flavor
Flavor or flavour is the sensory impression of a food or other substance, and is determined mainly by the chemical senses of taste and smell. The "trigeminal senses", which detect chemical irritants in the mouth and throat as well as temperature and texture, are also very important to the overall...
s and aromas that the wine should be expressing. Ultimately the quality of the wine is reduced, making it less appealing and sometimes undrinkable.
There are many causes for the perception in wine faults ranging from poor hygiene
Hygiene
Hygiene refers to the set of practices perceived by a community to be associated with the preservation of health and healthy living. While in modern medical sciences there is a set of standards of hygiene recommended for different situations, what is considered hygienic or not can vary between...
at the winery, excessive and/or insufficient exposure of the wine to oxygen
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
, excessive or insufficient exposure of the wine to sulphur, overextended maceration
Maceration (wine)
Maceration is the winemaking process where the phenolic materials of the grape— tannins, coloring agents and flavor compounds— are leached from the grape skins, seeds and stems into the must. Maceration is the process by which the red wine receives its red color, since 99% of all grape juice is...
of the wine either pre or post 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...
, faulty fining, filtering and stabilization of the wine, the use of dirty oak barrels, over extended barrel aging and the use of poor quality corks. Outside of the winery, other factors within the control of the retailer or end user of the wine can contribute to the perception of flaws in the wine. These include poor storage of the wine that exposes it to excessive heat and temperature fluctuations as well as the use of dirty stemware
Stemware
Stemware is drinkware that stands on stems above a base. It is usually made from glass, but may be made from ceramics or metals.Stemware includes:* Wine glasses* Champagne flutes* Chalices and goblets...
during wine tasting
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...
that can introduce materials or aromas to what was previously a clean and fault-free wine.
Differences between flaws and faults
In wine tasting, there is a distinction made between what is considered a flaw and a fault. Wine flaws are minor attributes that depart from what is perceived as a normal wine characteristics. These include excessive sulfur dioxideSulfur dioxide
Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...
, volatile acidity, Brettanomyces
Brettanomyces
Brettanomyces is a non-spore forming genus of yeast in the family Saccharomycetaceae, and is often colloquially referred to as "Brett". The genus name Dekkera is used interchangeably with Brettanomyces, as it describes the teleomorph or spore forming form of the yeast. The cellular morphology of...
or "Brett aromas" and diacetyl
Diacetyl
Diacetyl is a natural byproduct of fermentation. It is a vicinal diketone with the molecular formula C4H6O2...
or buttery aromas. The amount to which these aromas or attributes become excessive is dependent on the particular tastes and recognition threshold of the wine taster. Generally, a wine exhibiting these qualities is still considered drinkable by the large masses. However, some flaws such as volatile acidity and Brettanomyces can be considered a fault when they are in such an excess that they overwhelm other components of the wine. Wine faults are generally major attributes that make a wine undrinkable to most wine tasters. Examples of wine faults include acetaldehyde
Acetaldehyde
Acetaldehyde is an organic chemical compound with the formula CH3CHO or MeCHO. It is one of the most important aldehydes, occurring widely in nature and being produced on a large scale industrially. Acetaldehyde occurs naturally in coffee, bread, and ripe fruit, and is produced by plants as part...
(except when purposely induced in wines like Sherry
Sherry
Sherry is a fortified wine made from white grapes that are grown near the town of Jerez , Spain. In Spanish, it is called vino de Jerez....
and Rancio), ethyl acetate
Ethyl acetate
Ethyl acetate is the organic compound with the formula CH3COOCH2CH3. This colorless liquid has a characteristic sweet smell and is used in glues, nail polish removers, and cigarettes...
and cork taint
Cork taint
Cork taint is a broad term referring to a wine fault characterized by a set of undesirable smells or tastes found in a bottle of wine, especially spoilage that can only be detected after bottling, aging and opening...
.
Detecting faults in wine tasting
The vast majority of wine faults are detected by the nose and the distinctive aromas that they give off. However, the presence of some wine faults can be detected by visual and taste perceptions. For example, premature oxidation can be noticed by the yellowing and browning of the wine's color. The sign of gas bubbles in wines that are not meant to be sparkling can be a sign of refermentationFermentation (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...
or malolactic fermentation
Malolactic fermentation
Malolactic fermentation is a process in winemaking where tart-tasting malic acid, naturally present in grape must, is converted to softer-tasting lactic acid. Malolactic fermentation tends to create a rounder, fuller mouthfeel. It has been said that malic acid tastes of green apples...
happening in the bottle. Unusual breaks in the color of the wine could be a sign of excessive copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
, iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
or proteins that were not removed during fining or filtering. A wine with an unusual color for its variety or wine region could be a sign of excessive or insufficient maceration or as well as poor temperature controls during fermentation. Tactile clues of potential wine faults include the burning, acidic taste associated with volatile acidity that can make a wine seem out of balance.
| Wine fault | Characteristics |
| Acetaldehyde Acetaldehyde Acetaldehyde is an organic chemical compound with the formula CH3CHO or MeCHO. It is one of the most important aldehydes, occurring widely in nature and being produced on a large scale industrially. Acetaldehyde occurs naturally in coffee, bread, and ripe fruit, and is produced by plants as part... |
Smell of roasted nuts or dried out straw. Commonly associated with Sherries where these aromas are considered acceptable |
| Amyl-acetate | Smell of "fake" candy banana flavoring |
| Brettanomyces Brettanomyces Brettanomyces is a non-spore forming genus of yeast in the family Saccharomycetaceae, and is often colloquially referred to as "Brett". The genus name Dekkera is used interchangeably with Brettanomyces, as it describes the teleomorph or spore forming form of the yeast. The cellular morphology of... |
Smell of barnyards, fecal and gamey horse aromas |
| Cork taint Cork taint Cork taint is a broad term referring to a wine fault characterized by a set of undesirable smells or tastes found in a bottle of wine, especially spoilage that can only be detected after bottling, aging and opening... |
Smell of a damp basement, wet cardboard or newspapers and mushrooms |
| Diacetyl Diacetyl Diacetyl is a natural byproduct of fermentation. It is a vicinal diketone with the molecular formula C4H6O2... |
Smell of rancid butter |
| Ethyl acetate Ethyl acetate Ethyl acetate is the organic compound with the formula CH3COOCH2CH3. This colorless liquid has a characteristic sweet smell and is used in glues, nail polish removers, and cigarettes... |
Smell of vinegar, paint thinner and nail polish remover |
| Hydrogen sulfide Hydrogen sulfide Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million... |
Smell of rotten eggs or garlic that has gone bad |
| Iodine Iodine Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor.... |
Smell of moldy grapes |
| Lactic acid bacteria Lactic acid bacteria The lactic acid bacteria comprise a clade of Gram-positive, low-GC, acid-tolerant, generally non-sporulating, non-respiring rod or cocci that are associated by their common metabolic and physiological characteristics. These bacteria, usually found in decomposing plants and lactic products, produce... |
Smell of sauerkraut |
| Mercaptans | Smell of burnt rubber and/or cooked cabbage |
| Oxidation | Smell of cooked fruit and walnuts. Also detectable visually by premature browning or yellowing of the wine |
| Sorbic acid Sorbic acid Sorbic acid, or 2,4-hexadienoic acid, is a natural organic compound used as a food preservative. It has the chemical formula C6H8O2. It is a colourless solid that is slightly soluble in water and sublimes readily... plus lactic acid bacteria Lactic acid bacteria The lactic acid bacteria comprise a clade of Gram-positive, low-GC, acid-tolerant, generally non-sporulating, non-respiring rod or cocci that are associated by their common metabolic and physiological characteristics. These bacteria, usually found in decomposing plants and lactic products, produce... |
Smell of crushed geranium leaves |
| Sulfur dioxide Sulfur dioxide Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel... |
Smell of burnt matches. Can also come across as a pricking sensation in the nose. |
Oxidation
The oxidation of wine is perhaps the most common of wine faults, as the presence of oxygenOxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
and a catalyst are the only requirements for the process to occur. It is also known as maderized wine, from Madeira wine
Madeira wine
Madeira is a fortified Portuguese wine made in the Madeira Islands. Some wines produced in small quantities in California and Texas are also referred to as "Madeira", or "Madera", although those wines do not conform to the EU PDO regulations...
, which is intentionally oxidized.
Oxidation can occur throughout the winemaking process, and even after the wine has been bottled. Anthocyanin
Anthocyanin
Anthocyanins are water-soluble vacuolar pigments that may appear red, purple, or blue according to pH...
s, catechin
Catechin
Catechin is a natural phenol antioxidant plant secondary metabolite. The term catechins is also commonly used to refer to the related family of flavonoids and the subgroup flavan-3-ols ....
s, epicatechins and other phenols present in wine are those most easily oxidised , which leads to a loss of colour, flavour and aroma - sometimes referred to as flattening. In most cases compounds such as sulfur dioxide
Sulfur dioxide
Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...
or erythorbic acid
Erythorbic acid
Erythorbic acid, formerly known as isoascorbic acid and D-araboascorbic acid, is a stereoisomer of ascorbic acid . It is a vegetable-derived food additive produced from sucrose. It is denoted by E number E315, and is widely used as an antioxidant in processed foods.Clinical trials have been...
are added to wine by winemakers, which protect the wine from oxidation and also bind with some of the oxidation products to reduce their organoleptic effect. Apart from phenolic oxidation, the ethanol
Ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...
present within wine can also be oxidised into other compounds responsible for flavour and aroma taints.
Acetaldehyde
AcetaldehydeAcetaldehyde
Acetaldehyde is an organic chemical compound with the formula CH3CHO or MeCHO. It is one of the most important aldehydes, occurring widely in nature and being produced on a large scale industrially. Acetaldehyde occurs naturally in coffee, bread, and ripe fruit, and is produced by plants as part...
is an intermediate product of yeast 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...
; however, it is more commonly associated with ethanol
Ethanol
Ethanol, also called ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol, is a volatile, flammable, colorless liquid. It is a psychoactive drug and one of the oldest recreational drugs. Best known as the type of alcohol found in alcoholic beverages, it is also used in thermometers, as a...
oxidation catalysed by the enzyme ethanol dehydrogenase
Alcohol dehydrogenase
Alcohol dehydrogenases are a group of dehydrogenase enzymes that occur in many organisms and facilitate the interconversion between alcohols and aldehydes or ketones with the reduction of nicotinamide adenine dinucleotide...
. Acetaldehyde production is also associated with the presence of surface film forming yeasts and bacteria, such as acetic acid bacteria
Acetic acid bacteria
Acetic acid bacteria are bacteria that derive their energy from the oxidation of ethanol to acetic acid during fermentation. They are Gram-negative, aerobic, rod-shaped bacteria. Not to be confused with the genus Acetobacterium which are anaerobic homoacetogenic facultative autotrophs and can...
, which form the compound by the decarboxylation
Decarboxylation
Decarboxylation is a chemical reaction that releases carbon dioxide . Usually, decarboxylation refers to a reaction of carboxylic acids, removing a carbon atom from a carbon chain. The reverse process, which is the first chemical step in photosynthesis, is called carbonation, the addition of CO2 to...
of pyruvate. The sensory threshold
Sensory threshold
Sensory threshold is a theoretical concept used in psychophysics. A stimulus that is less intense than the sensory threshold will not elicit any sensation...
for acetaldehyde is 100-125 mg/L
Litre
pic|200px|right|thumb|One litre is equivalent to this cubeEach side is 10 cm1 litre water = 1 kilogram water The litre is a metric system unit of volume equal to 1 cubic decimetre , to 1,000 cubic centimetres , and to 1/1,000 cubic metre...
. Beyond this level it imparts a sherry
Sherry
Sherry is a fortified wine made from white grapes that are grown near the town of Jerez , Spain. In Spanish, it is called vino de Jerez....
type character to the wine which can also be described as green apple, sour and metallic. Acetaldehyde intoxication is also implicated in hangover
Hangover
A hangover describes the sum of unpleasant physiological effects following heavy consumption of alcoholic beverages. The most commonly reported characteristics of a hangover include headache, nausea, sensitivity to light and noise, lethargy, dysphoria, diarrhea and thirst, typically after the...
s.
Acetic acid
Acetic acidAcetic acid
Acetic acid is an organic compound with the chemical formula CH3CO2H . It is a colourless liquid that when undiluted is also called glacial acetic acid. Acetic acid is the main component of vinegar , and has a distinctive sour taste and pungent smell...
in wine, often referred to as volatile acidity (VA) or vinegar taint, can be contributed by many wine spoilage yeasts and bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
. This can be from either a by-product
By-product
A by-product is a secondary product derived from a manufacturing process or chemical reaction. It is not the primary product or service being produced.A by-product can be useful and marketable or it can be considered waste....
of fermentation, or due to the spoilage of finished wine. Acetic acid bacteria, such as those from the genera Acetobacter
Acetobacter
Acetobacter is a genus of acetic acid bacteria characterized by the ability to convert ethanol to acetic acid in the presence of oxygen. There are several species within this genus, and there are other bacteria capable of forming acetic acid under various conditions; but all of the Acetobacter are...
and Gluconobacter produce high levels of acetic acid. The sensory threshold
Sensory threshold
Sensory threshold is a theoretical concept used in psychophysics. A stimulus that is less intense than the sensory threshold will not elicit any sensation...
for acetic acid is >700 mg/L, with concentrations greater than 1.2-1.3 g/L becoming unpleasant.
There are different opinions as to what level of volatile acidity is appropriate for higher quality wine. Although too high a concentration is sure to leave an undesirable, 'vinegar' tasting wine, some wine's acetic acid levels are developed to create a more 'complex', desirable taste. The renowned 1947 Cheval Blanc
Château Cheval Blanc
Château Cheval Blanc , is a wine producer in Saint-Émilion in the Bordeaux wine region of France. Its wine is one of only two to receive the highest rank of Premier Grand Cru Classé status in the Classification of Saint-Émilion wine of 1955, along with Château Ausone.The estate's second wine is...
is widely recognized to contain high levels of volatile acidity.
Ethyl acetate
Ethyl acetate
Ethyl acetate is the organic compound with the formula CH3COOCH2CH3. This colorless liquid has a characteristic sweet smell and is used in glues, nail polish removers, and cigarettes...
is formed in wine by the esterification of ethanol and acetic acid. Therefore wines with high acetic acid levels are more likely to see ethyl acetate formation, but the compound does not contribute to the volatile acidity. It is a common microbial fault produced by wine spoilage yeasts, particularly Pichia anomala, Kloeckera apiculata, and Hanseniaspora uvarum. High levels of ethyl acetate are also produced by lactic acid bacteria
Lactic acid bacteria
The lactic acid bacteria comprise a clade of Gram-positive, low-GC, acid-tolerant, generally non-sporulating, non-respiring rod or cocci that are associated by their common metabolic and physiological characteristics. These bacteria, usually found in decomposing plants and lactic products, produce...
and acetic acid bacteria
Acetic acid bacteria
Acetic acid bacteria are bacteria that derive their energy from the oxidation of ethanol to acetic acid during fermentation. They are Gram-negative, aerobic, rod-shaped bacteria. Not to be confused with the genus Acetobacterium which are anaerobic homoacetogenic facultative autotrophs and can...
. The sensory threshold for ethyl acetate is 150–200 mg/L. Levels below this can give an added richness and sweetness, whereas levels above impart nail polish remover, glue
Glue
This is a list of various types of glue. Historically, the term "glue" only referred to protein colloids prepared from animal flesh. The meaning has been extended to refer to any fluid adhesive....
, or varnish
Varnish
Varnish is a transparent, hard, protective finish or film primarily used in wood finishing but also for other materials. Varnish is traditionally a combination of a drying oil, a resin, and a thinner or solvent. Varnish finishes are usually glossy but may be designed to produce satin or semi-gloss...
type aromas.
Sulfur compounds
SulfurSulfur
Sulfur 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...
is used as an additive
Food additive
Food additives are substances added to food to preserve flavor or enhance its taste and appearance.Some additives have been used for centuries; for example, preserving food by pickling , salting, as with bacon, preserving sweets or using sulfur dioxide as in some wines...
throughout the winemaking process, primarily to stop oxidation as mentioned above but also as antimicrobial
Antimicrobial
An anti-microbial is a substance that kills or inhibits the growth of microorganisms such as bacteria, fungi, or protozoans. Antimicrobial drugs either kill microbes or prevent the growth of microbes...
agent. When managed properly in wine, its presence there is often undetected, however when used recklessly it can contribute to flavour and aroma taints which are very volatile and potent. Sulfur compounds typically have low sensory thresholds.
Sulfur dioxide
Sulfur dioxide
Sulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...
is a common wine additive, used for its antioxidant
Antioxidant
An antioxidant is a molecule capable of inhibiting the oxidation of other molecules. Oxidation is a chemical reaction that transfers electrons or hydrogen from a substance to an oxidizing agent. Oxidation reactions can produce free radicals. In turn, these radicals can start chain reactions. When...
and preservative
Preservative
A preservative is a naturally occurring or synthetically produced substance that is added to products such as foods, pharmaceuticals, paints, biological samples, wood, etc. to prevent decomposition by microbial growth or by undesirable chemical changes....
properties. When its use is not managed well it can be overadded, with its perception in wine reminiscent of matchsticks, burnt rubber, or mothballs. Wines such as these are often termed sulfitic.
Hydrogen sulfide
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...
(H2S) is generally thought to be a metabolic by-product of yeast fermentation in nitrogen
Nitrogen
Nitrogen is a chemical element that has the symbol N, atomic number of 7 and atomic mass 14.00674 u. Elemental nitrogen is a colorless, odorless, tasteless, and mostly inert diatomic gas at standard conditions, constituting 78.08% by volume of Earth's atmosphere...
limited environments. It is formed when yeast ferments via the sulfate reduction pathway. Fermenting wine is often supplemented with diammonium phosphate
Diammonium phosphate
Diammonium phosphate is one of a series of water-soluble ammonium phosphate salts which can be produced when ammonia reacts with phosphoric acid...
(DAP) as a nitrogen source to prevent H2S formation. The sensory threshold for hydrogen sulfide is 8-10 μg/L, with levels above this imparting a distinct rotten egg aroma to the wine. Hydrogen sulfide can further react with wine compounds to form mercaptans and disulfide
Disulfide
In chemistry, a disulfide usually refers to the structural unit composed of a linked pair of sulfur atoms. Disulfide usually refer to a chemical compound that contains a disulfide bond, such as diphenyl disulfide, C6H5S-SC6H5....
s.
Mercaptans
Methionine
Methionine is an α-amino acid with the chemical formula HO2CCHCH2CH2SCH3. This essential amino acid is classified as nonpolar. This amino-acid is coded by the codon AUG, also known as the initiation codon, since it indicates mRNA's coding region where translation into protein...
. They can be formed if finished wine is allowed prolonged contact with the lees
Lees (fermentation)
Lees refers to deposits of dead yeast or residual yeast and other particles that precipitate, or are carried by the action of "fining", to the bottom of a vat of wine after fermentation and ageing. The yeast deposits in beer brewing are known as trub...
. This can be prevented by racking
Racking
Racking is the process of siphoning the wine or beer off the lees into a new, clean barrel or in the case of beer off the trub. Racking allows clarification and aids in stabilization. Wine that is allowed to age on the lees often develops "off-tastes". A racking hose or tubing is used and can be...
the wine. Mercaptans have a very low sensory threshold, around 1.5 µg/L
Litre
pic|200px|right|thumb|One litre is equivalent to this cubeEach side is 10 cm1 litre water = 1 kilogram water The litre is a metric system unit of volume equal to 1 cubic decimetre , to 1,000 cubic centimetres , and to 1/1,000 cubic metre...
, with levels above causing onion, rubber, and skunk type odours.
Dimethyl sulfide
Dimethyl sulfide
Dimethyl sulfide or methylthiomethane is an organosulfur compound with the formula 2S. Dimethyl sulfide is a water-insoluble flammable liquid that boils at and has a characteristic disagreeable odor. It is a component of the smell produced from cooking of certain vegetables, notably maize,...
(DMS) is naturally present in most wines, probably from the breakdown of sulfur containing amino acids. Like ethyl acetate, levels of DMS below the sensory threshold can have a positive effect on flavour, contributing to fruityness, fullness, and complexity. Levels above the sensory threshold of >30 µg/L in white wines and >50 µg/L for red wines, give the wine characteristics of cooked cabbage, canned corn, asparagus or truffles. Note that dimethyl sulfide is not formed from the oxidation of mercaptans, but dimethyl disulfide
Dimethyl disulfide
Dimethyl disulfide is an organic chemical compound with the molecular formula CH3SSCH3 which is the simplest disulfide. It is a flammable liquid with an unpleasant odor.DMDS can be produced by the reaction of methanethiol with sulfur:-Uses:...
is.
Cork taint
Cork taint is a wine fault mostly attributed to the compound 2,4,6-trichloroanisole
2,4,6-Trichloroanisole
2,4,6-Trichloroanisole is a chemical compound that is a chlorinated derivative of anisole.Trichloroanisole is a fungal metabolite of 2,4,6-trichlorophenol, which is used as a fungicide. It can be found in minute traces on packaging materials stored in the presence of fiberboard treated with...
(TCA), although other compounds such as guaiacol
Guaiacol
Guaiacol is a naturally occurring organic compound with the formula C6H4. Although it is biosynthesized by a variety of organisms, this colorless aromatic oil is usually derived from guaiacum or wood creosote. Samples darken upon exposure to air and light. Guaiacol is present in wood smoke,...
, geosmin
Geosmin
Geosmin, which literally translates to "earth smell", is an organic compound with a distinct earthy flavour and aroma, and is responsible for the earthy taste of beets and a contributor to the strong scent that occurs in the air when rain falls after a dry spell of weather or when soil is...
, 2-methylisoborneol
2-Methylisoborneol
2-Methylisoborneol is an organic chemical with a strong odor. It is a derivate of borneol. Its odor detection threshold is very low and it is one of the chemicals with major influence on the quality of drinking water...
, 1-octen-3-ol
1-Octen-3-ol
1-Octen-3-ol, octenol for short , is a chemical that attracts biting insects such as mosquitos. It is contained in human breath and sweat, and it was once believed that insect repellent DEET works by blocking the insects' octenol odorant receptors.Octenol is used in combination with carbon dioxide...
, 1-octen-3-one, 2,3,4,6-tetrachloroanisole, pentachloroanisole, and 2,4,6-tribromoanisole
2,4,6-Tribromoanisole
2,4,6-Tribromoanisole is a chemical compound that is a brominated derivative of anisole. It is one of the chemicals responsible for cork taint....
are also thought to be involved. TCA most likely originates as a metabolite
Metabolite
Metabolites are the intermediates and products of metabolism. The term metabolite is usually restricted to small molecules. A primary metabolite is directly involved in normal growth, development, and reproduction. Alcohol is an example of a primary metabolite produced in large-scale by industrial...
of mould growth on chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
-bleached wine corks and barrels. It causes earthy, mouldy, and musty aromas in wine that easily mask the natural fruit aromas, making the wine very unappealing. Wines in this state are often described as "corked". As cork taint has gained a wide reputation as a wine fault, other faults are often mistakenly attributed to it.
Heat damage
Heat damaged wines are often casually referred to as cooked, which suggests how heat can affect a wine. The ideal storage temperature for wine is generally accepted to be 13°C (55°F). Wines that are stored at temperatures greatly higher than this will experience an increased aging rate. Wines exposed to extreme temperatures will thermally expandThermal expansion
Thermal expansion is the tendency of matter to change in volume in response to a change in temperature.When a substance is heated, its particles begin moving more and thus usually maintain a greater average separation. Materials which contract with increasing temperature are rare; this effect is...
, and may even push up between the cork and bottle and leak from the top. When opening a bottle of wine, if a track of wine is visible along the length of the cork, the cork is partially pushed out of the bottle, or wine is visible on the top of the cork while it is still in the bottle, it has most likely been heat damaged. Heat damaged wines often become oxidized, and red wines may take on a brick color.
Even if the temperatures do not reach extremes, temperature variation alone can also damage bottled wine through oxidation. All corks allow some leakage of air (hence old wines become increasingly oxidized), and temperature fluctuations will vary the pressure differential between the inside and outside of the bottle and will act to "pump" air into the bottle at a faster rate than will occur at any temperature strictly maintained.
Reputedly, heat damage is the most widespread and common problem found in wines. It often goes unnoticed because of the prevalence of the problem, consumers don't know it's possible, and most often would just chalk the problem up to poor quality, or other factors.
Lightstrike
Lightstruck wines are those that have had excessive exposure to ultravioletUltraviolet
Ultraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than X-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
light, particularly in the range 325 to 450 nm. Very delicate wines, such as Champagnes, are generally worst affected, with the fault causing a wet cardboard or wet wool type flavour and aroma. Red wines rarely become lightstruck because of the phenolic compounds present within the wine that protect it. Lightstrike is thought to be caused by sulfur compounds such as dimethyl sulfide
Dimethyl sulfide
Dimethyl sulfide or methylthiomethane is an organosulfur compound with the formula 2S. Dimethyl sulfide is a water-insoluble flammable liquid that boils at and has a characteristic disagreeable odor. It is a component of the smell produced from cooking of certain vegetables, notably maize,...
. In France lightstrike is known as "goût de lumière", which translates to a taste of light. The fault explains why wines are generally bottled in coloured glass, which blocks the ultraviolet light, and why wine should be stored in dark environments.
Ladybird taint
Some insects present in the grapes at harvest inevitably end up in the press and for the most part are inoffensive. Others, notably types of ladybirds, or the multicoloured asian lady beetle, release unpleasant volatile compounds as a defensive mechanism when disturbed. In sufficient quantities these can affect the wine's bouquet and taste. With an olfactory detection threshold of a few ppb, the principal active compounds are methoxypyrazines, or pyrazinePyrazine
Pyrazine is a heterocyclic aromatic organic compound with the chemical formula C4H4N2.Pyrazine is a symmetrical molecule with point group D2h. Derivatives like phenazine are well known for their antitumor, antibiotic and diuretic activity. Pyrazine is less basic in nature than pyridine, pyridazine...
s, that are perceived as rancid peanut butter
Peanut butter
Peanut butter is a food paste made primarily from ground dry roasted peanuts, popular in North America, Netherlands, United Kingdom, and parts of Asia, particularly the Philippines and Indonesia. It is mainly used as a sandwich spread, sometimes in combination as in the peanut butter and jelly...
, bitter herbaceous, green bell pepper
Bell pepper
Bell pepper, also known as sweet pepper or a pepper and capsicum , is a cultivar group of the species Capsicum annuum . Cultivars of the plant produce fruits in different colors, including red, yellow, orange and green. Bell peppers are sometimes grouped with less pungent pepper varieties as...
, or cat urine. This is also a naturally occurring compound in Sauvignon grapes and so ladybug taint has been known to make Riesling
Riesling
Riesling 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...
s taste like 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...
.
Brettanomyces (Dekkera)
The yeast Brettanomyces
Brettanomyces
Brettanomyces is a non-spore forming genus of yeast in the family Saccharomycetaceae, and is often colloquially referred to as "Brett". The genus name Dekkera is used interchangeably with Brettanomyces, as it describes the teleomorph or spore forming form of the yeast. The cellular morphology of...
produces an array of metabolite
Metabolite
Metabolites are the intermediates and products of metabolism. The term metabolite is usually restricted to small molecules. A primary metabolite is directly involved in normal growth, development, and reproduction. Alcohol is an example of a primary metabolite produced in large-scale by industrial...
s when growing in wine, some of which are volatile phenolic compounds. Together these compounds are often referred to as "Brettanomyces character", or simply "Brett". The main constituents are listed below, with their sensory threshold and common sensory descriptors:
- 4-ethylphenol4-Ethylphenol4-Ethylphenol, often abbreviated to 4-EP, is a phenolic compound with the molecular formula C8H10O. In wine and beer it is produced by the spoilage yeast Brettanomyces. When it reaches concentrations greater than the sensory threshold it can give the wine aromas described as barnyard, medicinal,...
(>140 µg/L): Band-aids, barnyard, horse stable, antiseptic - 4-ethylguaiacol (>600 µg/L): Bacon, spice, cloves, smoky
- isovaleric acid3-Methylbutanoic acid3-Methylbutanoic acid, or more commonly isovaleric acid, is a natural fatty acid found in a wide variety of plants and essential oils. Isovaleric acid is clear colorless liquid that is sparingly soluble in water, but extremely soluble in most common organic solvents.Isovaleric acid has a strong...
: Sweaty, cheese, rancidity
Geosmin
GeosminGeosmin
Geosmin, which literally translates to "earth smell", is an organic compound with a distinct earthy flavour and aroma, and is responsible for the earthy taste of beets and a contributor to the strong scent that occurs in the air when rain falls after a dry spell of weather or when soil is...
is a compound with a very distinct earthy, musty, beetroot, even turnip flavour and aroma and has an extremely low sensory threshold of down to 10 parts per trillion. Its presence in wine is usually derived as metabolite from the growth of filamentous actinomycetes
Actinobacteria
Actinobacteria are a group of Gram-positive bacteria with high guanine and cytosine content. They can be terrestrial or aquatic. Actinobacteria is one of the dominant phyla of the bacteria....
such as Streptomyces
Streptomyces
Streptomyces is the largest genus of Actinobacteria and the type genus of the family Streptomycetaceae. Over 500 species of Streptomyces bacteria have been described. As with the other Actinobacteria, streptomycetes are gram-positive, and have genomes with high guanine and cytosine content...
, and mould
Mold
Molds are fungi that grow in the form of multicellular filaments called hyphae. Molds are not considered to be microbes but microscopic fungi that grow as single cells called yeasts...
s such as Botrytis cinerea
Botrytis cinerea
Botrytis cinerea is a necrotrophic fungus that affects many plant species, although its most notable hosts may be wine grapes. In viticulture, it is commonly known as botrytis bunch rot; in horticulture, it is usually called grey mould or gray mold.The fungus gives rise to two different kinds of...
and Penicillium expansum, on grapes. Wines affected by but not attributed to geosmins are often thought to have earthy properties due to terroir
Terroir
Terroir comes from the word terre "land". It was originally a French term in wine, coffee and tea used to denote the special characteristics that the geography, geology and climate of a certain place bestowed upon particular varieties...
. The geosmin fault occurs worldwide and has been found in recent vintages of red wines from Beaujolais
Beaujolais
Beaujolais is a French Appellation d'Origine Contrôlée wine generally made of the Gamay grape which has a thin skin and is low in tannins. Like most AOC wines they are not labeled varietally. Whites from the region, which make up only 1% of its production, are made mostly with Chardonnay grapes...
, Bordeaux
Bordeaux
Bordeaux is a port city on the Garonne River in the Gironde department in southwestern France.The Bordeaux-Arcachon-Libourne metropolitan area, has a population of 1,010,000 and constitutes the sixth-largest urban area in France. It is the capital of the Aquitaine region, as well as the prefecture...
, Burgundy
Burgundy wine
Burgundy wine is wine made in the Burgundy region in eastern France, in the valleys and slopes west of the Saône River, a tributary of the Rhône. The most famous wines produced here - those commonly referred to as "Burgundies" - are red wines made from Pinot Noir grapes or white wines made from...
and the Loire
Loire
Loire is an administrative department in the east-central part of France occupying the River Loire's upper reaches.-History:Loire was created in 1793 when after just 3½ years the young Rhône-et-Loire department was split into two. This was a response to counter-Revolutionary activities in Lyon...
in France. Geosmin is also thought to be a contributing factor in cork taint
Cork taint
Cork taint is a broad term referring to a wine fault characterized by a set of undesirable smells or tastes found in a bottle of wine, especially spoilage that can only be detected after bottling, aging and opening...
.
Lactic acid bacteria
Lactic acid bacteriaLactic acid bacteria
The lactic acid bacteria comprise a clade of Gram-positive, low-GC, acid-tolerant, generally non-sporulating, non-respiring rod or cocci that are associated by their common metabolic and physiological characteristics. These bacteria, usually found in decomposing plants and lactic products, produce...
have a useful role in winemaking converting malic acid to lactic acid in malolactic fermentation
Malolactic fermentation
Malolactic fermentation is a process in winemaking where tart-tasting malic acid, naturally present in grape must, is converted to softer-tasting lactic acid. Malolactic fermentation tends to create a rounder, fuller mouthfeel. It has been said that malic acid tastes of green apples...
. However after this function has completed the bacteria may still be present within the wine, where they can metabolise other compounds and produce wine faults. Wines that have not undergone malolactic fermentation may be contaminated with lactic acid bacteria, leading to refermentation of the wine with it becoming turbid
Turbidity
Turbidity is the cloudiness or haziness of a fluid caused by individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality....
, swampy, and slightly effervescent
Effervescence
Effervescence might refer to one of the following:*Effervescence is the escape of gas from an aqueous solution.*Collective effervescence is a perceived energy formed by a gathering of people....
or spritzy. This can be avoided by sterile filtering wine directly before bottling. Lactic acid bacteria can also be responsible for other wine faults such as those below.
Bitterness taint
Pediococcus
Pediococcus is a genus of Gram-positive lactic acid bacteria, placed within the family of Lactobacillaceae. They usually occur in pairs or tetrads, and divide along two planes of symmetry, as do the other lactic acid cocci genera Aerococcus and Tetragenococcus. They are purely homofermentative...
, Lactobacillus
Lactobacillus
Lactobacillus is a genus of Gram-positive facultative anaerobic or microaerophilic rod-shaped bacteria. They are a major part of the lactic acid bacteria group, named as such because most of its members convert lactose and other sugars to lactic acid. They are common and usually benign...
, and Oenococcus
Oenococcus
Oenococcus is a genus of Gram-positive bacteria, placed within the family of Leuconostocaceae. The only species in the genus used to be Oenococcus oeni . In 2006, the species Oenococcus kitaharae was identified...
. It begins by the degradation of glycerol
Glycerol
Glycerol is a simple polyol compound. It is a colorless, odorless, viscous liquid that is widely used in pharmaceutical formulations. Glycerol has three hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature. The glycerol backbone is central to all lipids...
, a compound naturally found in wine at levels of 5-8 g/L, via a dehydratase
Dehydratase
Dehydratase is an enzyme that catalyzes the removal of oxygen and hydrogen from organic compounds in the form of water. This process is also known as dehydration.There are four classes of dehydratases:...
enzyme to 3-hydroxypropionaldehyde. During ageing this is further dehydrated to acrolein
Acrolein
Acrolein is the simplest unsaturated aldehyde. It is produced widely but is most often immediately reacted with other products due to its instability and toxicity...
which reacts with the anthocyanin
Anthocyanin
Anthocyanins are water-soluble vacuolar pigments that may appear red, purple, or blue according to pH...
s and other phenols present within the wine to form the taint. As red wines contain high levels of anthocyanins they are generally more susceptible.
Diacetyl
Diacetyl
Diacetyl is a natural byproduct of fermentation. It is a vicinal diketone with the molecular formula C4H6O2...
in wine is produced by lactic acid bacteria
Lactic acid bacteria
The lactic acid bacteria comprise a clade of Gram-positive, low-GC, acid-tolerant, generally non-sporulating, non-respiring rod or cocci that are associated by their common metabolic and physiological characteristics. These bacteria, usually found in decomposing plants and lactic products, produce...
, mainly Oenococcus oeni
Oenococcus oeni
Oenococcus oeni is a Gram-positive bacteria species in the genus of Oenococcus. It used to be the only species in the genus . In 2006, the species Oenococcus kitaharae was identified...
. In low levels it can impart positive nutty or caramel characters, however at levels above 5 mg/L it creates an intense buttery or butterscotch
Butterscotch
Butterscotch is a type of confectionery whose primary ingredients are brown sugar and butter, although other ingredients such as corn syrup, cream, vanilla, and salt are part of some recipes...
flavour, where it is perceived as a flaw. The sensory threshold for the compound can vary depending on the levels of certain wine components, such as sulfur dioxide. It can be produced as a metabolite of citric acid
Citric acid
Citric acid is a weak organic acid. It is a natural preservative/conservative and is also used to add an acidic, or sour, taste to foods and soft drinks...
when all of the malic acid
Malic acid
Malic acid is an organic compound with the formula HO2CCH2CHOHCO2H. It is a dicarboxylic acid which is made by all living organisms, contributes to the pleasantly sour taste of fruits, and is used as a food additive. Malic acid has two stereoisomeric forms , though only the L-isomer exists...
has been consumed. Diacetyl rarely taints wine to levels where it becomes undrinkable.
Geranium taint
Pelargonium
Pelargonium is a genus of flowering plants which includes about 200 species of perennials, succulents, and shrubs, commonly known as scented geraniums or storksbills. Confusingly, Geranium is the correct botanical name of a separate genus of related plants often called Cranesbills. Both Geranium...
leaves. The compound responsible is 2-ethoxyhexa-3,5-diene, which has a low sensory threshold concentration of 0.1 mg/L. In wine it is formed during the metabolism
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
of potassium sorbate
Potassium sorbate
Potassium sorbate is the potassium salt of sorbic acid, chemical formula C6H7KO2. Its primary use is as a food preservative . Potassium sorbate is effective in a variety of applications including food, wine, and personal care products....
by lactic acid bacteria
Lactic acid bacteria
The lactic acid bacteria comprise a clade of Gram-positive, low-GC, acid-tolerant, generally non-sporulating, non-respiring rod or cocci that are associated by their common metabolic and physiological characteristics. These bacteria, usually found in decomposing plants and lactic products, produce...
. Potassium sorbate is sometimes added to wine as a preservative
Preservative
A preservative is a naturally occurring or synthetically produced substance that is added to products such as foods, pharmaceuticals, paints, biological samples, wood, etc. to prevent decomposition by microbial growth or by undesirable chemical changes....
against yeast, however its use is generally kept to a minimum due to the possibility of the taint developing. The production of the taint begins with the conversion of sorbic acid
Sorbic acid
Sorbic acid, or 2,4-hexadienoic acid, is a natural organic compound used as a food preservative. It has the chemical formula C6H8O2. It is a colourless solid that is slightly soluble in water and sublimes readily...
to the alcohol sorbinol. The alcohol is then isomerised
Isomerisation
In chemistry isomerisation is the process by which one molecule is transformed into another molecule which has exactly the same atoms, but the atoms are rearranged e.g. A-B-C → B-A-C . In some molecules and under some conditions, isomerisation occurs spontaneously...
in the presence of acid to 3,5-hexadiene-2-ol, which is then esterified with ethanol to form 2-ethoxy-3,5-hexadiene
Must
Must is freshly pressed fruit juice that contains the skins, seeds, and stems of the fruit. The solid portion of the must is called pomace; it typically makes up 7%–23% of the total weight of the must. Making must is the first step in winemaking...
.
Mannitol
Mannitol
Mannitol is a white, crystalline organic compound with the formula . This polyol is used as an osmotic diuretic agent and a weak renal vasodilator...
is a sugar alcohol
Sugar alcohol
A sugar alcohol is a hydrogenated form of carbohydrate, whose carbonyl group has been reduced to a primary or secondary hydroxyl group . Sugar alcohols have the general formula Hn+1H, whereas sugars have HnHCO...
, and in wine it is produced by heterofermentative lactic acid bacteria, such as Lactobacillus brevis
Lactobacillus brevis
Lactobacillus brevis is a species of lactic acid bacteria. It can be found in many different environments and in fermented foods such as sauerkraut and pickles. It is also one of the most common causes of beer spoilage. Ingestion has been shown to improve human immune function, and it has been...
, by the reduction
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
of fructose
Fructose
Fructose, or fruit sugar, is a simple monosaccharide found in many plants. It is one of the three dietary monosaccharides, along with glucose and galactose, that are absorbed directly into the bloodstream during digestion. Fructose was discovered by French chemist Augustin-Pierre Dubrunfaut in 1847...
. Its perception is often complicated as it generally exists in wine alongside other faults, but it is usually described as viscous, ester
Ester
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...
-like combined with a sweet and irritating finish. Mannitol is usually produced in wines that undergo malolactic fermentation with a high level of residual sugars still present.
Ropiness
Ropiness is manifested as an increase in viscosityViscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
and a slimey or fatty mouthfeel of a wine. In France the fault is known as "graisse", which translates to fat. The problem stems from the production of dextrin
Dextrin
Dextrins are a group of low-molecular-weight carbohydrates produced by the hydrolysis of starch or glycogen. Dextrins are mixtures of polymers of D-glucose units linked by α- or α- glycosidic bonds....
s and polysaccharide
Polysaccharide
Polysaccharides are long carbohydrate molecules, of repeated monomer units joined together by glycosidic bonds. They range in structure from linear to highly branched. Polysaccharides are often quite heterogeneous, containing slight modifications of the repeating unit. Depending on the structure,...
s by certain lactic acid bacteria, particularly of the genera Leuconostoc
Leuconostoc
Leuconostoc is a genus of Gram-positive bacteria, placed within the family of Leuconostocaceae. They are generally ovoid cocci often forming chains. Leuconostoc spp. are intrinsically resistant to vancomycin and are catalase-negative . All species within this genus are heterofermentative and are...
and Pediococcus
Pediococcus
Pediococcus is a genus of Gram-positive lactic acid bacteria, placed within the family of Lactobacillaceae. They usually occur in pairs or tetrads, and divide along two planes of symmetry, as do the other lactic acid cocci genera Aerococcus and Tetragenococcus. They are purely homofermentative...
.
Mousiness
Lactic acid bacteria
The lactic acid bacteria comprise a clade of Gram-positive, low-GC, acid-tolerant, generally non-sporulating, non-respiring rod or cocci that are associated by their common metabolic and physiological characteristics. These bacteria, usually found in decomposing plants and lactic products, produce...
Lactobacillus brevis
Lactobacillus brevis
Lactobacillus brevis is a species of lactic acid bacteria. It can be found in many different environments and in fermented foods such as sauerkraut and pickles. It is also one of the most common causes of beer spoilage. Ingestion has been shown to improve human immune function, and it has been...
, Lactobacillus fermentum
Lactobacillus fermentum
Lactobacillus fermentum is a Gram-positive species of bacterium in the genus Lactobacillus. It is associated with active dental caries lesions. It is also commonly found in fermenting animal and plant material. It has been found in sourdough...
, and Lactobacillus hilgardii, and hence can occur in malolactic fermentation
Malolactic fermentation
Malolactic fermentation is a process in winemaking where tart-tasting malic acid, naturally present in grape must, is converted to softer-tasting lactic acid. Malolactic fermentation tends to create a rounder, fuller mouthfeel. It has been said that malic acid tastes of green apples...
. The compounds responsible are lysine
Lysine
Lysine is an α-amino acid with the chemical formula HO2CCH4NH2. It is an essential amino acid, which means that the human body cannot synthesize it. Its codons are AAA and AAG....
derivatives, mainly;
- 2-acetyl-3,4,5,6-tetrahydropyridine
- 2-acetyl-1,4,5,6-tetrahydropyridine
- 2-ethyltetrahydropyridine
- 2-acetyl-1-pyrrolene
The taints are not volatile at the 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...
of wine, and therefore not obvious as an aroma. However, when mixed with the slightly basic pH of saliva they can become very apparent on the palate, especially at the back of the mouth, as mouse cage or mouse urine.
Refermentation
Refermentation, sometimes called secondary fermentation, is caused by yeasts refermenting the residual sugar present within bottled wine. It occurs when sweet winesSweetness of wine
The subjective sweetness of a wine is determined by the interaction of several factors, including the amount of sugar in the wine to be sure, but also the relative levels of alcohol, acids, and tannins. Briefly: sugars and alcohol enhance a wine's sweetness; acids and bitter tannins counteract it...
are bottled in non-sterile
Asepsis
Asepsis is the state of being free from disease-causing contaminants or, preventing contact with microorganisms. The term asepsis often refers to those practices used to promote or induce asepsis in an operative field in surgery or medicine to prevent infection...
conditions, allowing the presence of microorganisms. The most common yeast to referment wine is the standard wine fermentation yeast Saccharomyces cerevisiae
Saccharomyces cerevisiae
Saccharomyces cerevisiae is a species of yeast. It is perhaps the most useful yeast, having been instrumental to baking and brewing since ancient times. It is believed that it was originally isolated from the skin of grapes...
, but has also been attributed to Schizosaccharomyces pombe
Schizosaccharomyces pombe
Schizosaccharomyces pombe, also called "fission yeast", is a species of yeast. It is used as a model organism in molecular and cell biology. It is a unicellular eukaryote, whose cells are rod-shaped. Cells typically measure 3 to 4 micrometres in diameter and 7 to 14 micrometres in length...
and Zygosaccharomyces bailii
Zygosaccharomyces bailii
Zygosaccharomyces bailii is the type species for the genus Zygosaccharomyces. It was initially described as Saccharomyces bailii by Lindner in 1895, but in 1983 was reclassified as Zygosaccharomyces bailii in the work by Barnett et al....
. The main issues associated with the fault include turbidity
Turbidity
Turbidity is the cloudiness or haziness of a fluid caused by individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality....
(from yeast biomass
Biomass
Biomass, as a renewable energy source, is biological material from living, or recently living organisms. As an energy source, biomass can either be used directly, or converted into other energy products such as biofuel....
production), excess ethanol production (may violate labelling
Wine label
Wine labels are important sources of information for consumers since they tell the type and origin of the wine. The label is often the only resource a buyer has for evaluating the wine before purchasing it...
laws), slight carbonation
Carbonation
Carbonation is the process of dissolving carbon dioxide in water. The process usually involves carbon dioxide under high pressure. When the pressure is reduced, the carbon dioxide is released from the solution as small bubbles, which cause the solution to "fizz." This effect is seen in carbonated...
, and some coarse odours. Refermentation can be prevented by bottling wines dry (with residual sugar levels <1.0g/L), sterile filtering wine prior to bottling, or adding preservative chemicals such as dimethyl dicarbonate
Dimethyl dicarbonate
Dimethyl dicarbonate or DMDC is a colourless liquid with a sharp odour. Its primary use is as a beverage preservative and or processing aid or sterilant , and acts by inhibiting the enzymes acetate kinase and L-glutamic acid decarboxylase...
. The Portuguese wine
Portuguese wine
Portuguese wine is the result of traditions introduced to the region by ancient civilizations, such as the Phoenicians, Carthaginians, Greeks, and mostly the Romans. Portugal started to export its wines to Rome during the Roman Empire. Modern exports developed with trade to England after the...
style known as "vinhos verdes
Vinho Verde
Vinho Verde is a Portuguese wine from the Minho region in the far north of the country. The name literally means "Green Wine" , referring to its youthful freshness that leads to a very slight green color on the edges of the wine. The region is characterized by its many small growers, which...
" relies on this
secondary fermentation in bottle to impart a slight spritziness to the wine.
External links
- Organoleptic defects in wine (PDF document)
- The influence of microorganisms in winemaking (PDF document)
- Bad Wine, in New York magazine
- How to Spot Faulty Wine, from The Wine Doctor
- Wine Flaws: Reduction, in Sommelier JournalSommelier JournalSommelier Journal is a subscription-based magazine publication, founded in 2008 for sommeliers and others in the restaurant and wine business. The magazine summarizes consumer, restaurant, and wine trends and news for wine professionals.-History:...
- Wine Flaws: Oxidation, in Sommelier JournalSommelier JournalSommelier Journal is a subscription-based magazine publication, founded in 2008 for sommeliers and others in the restaurant and wine business. The magazine summarizes consumer, restaurant, and wine trends and news for wine professionals.-History:...
- Wine Flaws: Brettanomyces, in Sommelier JournalSommelier JournalSommelier Journal is a subscription-based magazine publication, founded in 2008 for sommeliers and others in the restaurant and wine business. The magazine summarizes consumer, restaurant, and wine trends and news for wine professionals.-History:...
- Wine Flaws: TCA in Sommelier JournalSommelier JournalSommelier Journal is a subscription-based magazine publication, founded in 2008 for sommeliers and others in the restaurant and wine business. The magazine summarizes consumer, restaurant, and wine trends and news for wine professionals.-History:...