Wine defect
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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 be of issue. 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 In psychophysics, sensory threshold is the weakest stimulus that an organism can sense. Unless otherwise indicated, it is usually defined as the weakest stimulus that can be detected half the time, for example, as indicated by a point on a probabi ...
, they replace or obscure the
flavor Flavor or flavour is either the sensory perception of taste or smell, or a flavoring in food that produces such perception. Flavor or flavour may also refer to: Science *Flavors (programming language), an early object-oriented extension to Lis ...
s and aromas that the wine should be expressing (or that the winemaker wants the wine to express). Ultimately the quality of the wine is reduced, making it less appealing and sometimes undrinkable.M. Baldy: ''"The University Wine Course", Third Edition, pp. 37-39, 69-80, 134-140. The Wine Appreciation Guild 2009 . There are many causes for the perception in wine faults, including poor hygiene at the winery, excessive or insufficient exposure of the wine to oxygen, excessive or insufficient exposure of the wine to
sulphur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...
, overextended maceration of the wine either pre- or post-
fermentation Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food ...
, faulty
fining, filtering and stabilization of the wine In winemaking, clarification and stabilization are the processes by which insoluble matter suspended in the wine is removed before bottling. This matter may include dead yeast cells ( lees), bacteria, tartrates, proteins, pectins, various tannin ...
, the use of dirty
oak barrels Oak is used in winemaking to vary the color, flavor, tannin profile and texture of wine. It can be introduced in the form of a barrel during the fermentation or aging periods, or as free-floating chips or staves added to wine fermented in a v ...
, 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.D. Bird: ''"Understanding Wine Technology"'', pp. 31-82, 155-184, 202-222. DBQA Publishing 2005 .


Differences between flaws and faults

In wine tasting, there is a big distinction made between what is considered a ''flaw'' and a ''fault''. Wine flaws are minor attributes that depart from what are perceived as normal wine characteristics. These include excessive
sulfur dioxide Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic activ ...
,
volatile acidity 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 ...
, '' 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 Recognition may refer to: *Award, something given in recognition of an achievement Machine learning *Pattern recognition, a branch of machine learning which encompasses the meanings below Biometric *Recognition of human individuals, or biometr ...
of the wine taster. Generally, a wine exhibiting these qualities is still considered drinkable by most people. 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 (IUPAC systematic name ethanal) is an organic chemical compound with the formula CH3 CHO, sometimes abbreviated by chemists as MeCHO (Me = methyl). It is a colorless liquid or gas, boiling near room temperature. It is one of the mos ...
(except when purposely induced in wines like Sherry and Rancio), ethyl acetate and cork taint.


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 color of wine is one of the most easily recognizable characteristics of wines. Color is also an element in wine tasting since heavy wines generally have a deeper color. The accessory traditionally used to judge the wine color was the tastevin, ...
. The sign of gas bubbles in wines that are not meant to be sparkling can be a sign of
refermentation Brewing is the production of beer by steeping a starch source (commonly cereal grains, the most popular of which is barley) in water and fermenting the resulting sweet liquid with yeast. It may be done in a brewery by a commercial brewer ...
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 Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
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 as well as poor temperature controls during fermentation. Tactile clues of potential wine faults include the burning, acidic taste associated with
volatile acidity 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 ...
that can make a wine seem out of balance.


Oxidation

The oxidation of wine is perhaps the most common of wine faults, as the presence of oxygen and a catalyst are the only requirements for the process to occur. Oxidation can occur throughout the winemaking process, and even after the wine has been bottled.
Anthocyanin Anthocyanins (), also called anthocyans, are water-soluble vacuolar pigments that, depending on their pH, may appear red, purple, blue, or black. In 1835, the German pharmacist Ludwig Clamor Marquart gave the name Anthokyan to a chemical compo ...
s, catechins, epicatechins and other phenols present in wine are those most easily oxidised,duToit, W.J. (2005)
Oxygen in winemaking: Part I
WineLand, accessed on 2 April 2006.
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 (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic activ ...
or
erythorbic acid Erythorbic acid (isoascorbic acid, D-araboascorbic acid) is a stereoisomer of ascorbic acid (vitamin C). It is synthesized by a reaction between methyl 2-keto-D-gluconate and sodium methoxide. It can also be synthesized from sucrose or by strains ...
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.Goode, Jamie (06/25/19)
Oxidation in wine
. ''internationalwinechallenge.com'', accessed on 10 February 2021.
Apart from phenolic oxidation, the ethanol present within wine can also be oxidised into other compounds responsible for flavour and aroma taints. Some wine styles can be oxidised intentionally, as in certain Sherry wines and Vin jaune from the Jura region of France.


Acetaldehyde

Acetaldehyde Acetaldehyde (IUPAC systematic name ethanal) is an organic chemical compound with the formula CH3 CHO, sometimes abbreviated by chemists as MeCHO (Me = methyl). It is a colorless liquid or gas, boiling near room temperature. It is one of the mos ...
is an intermediate product of yeast
fermentation Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food ...
; 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 Decarboxylation is a chemical reaction that removes a carboxyl group and releases carbon dioxide (CO2). Usually, decarboxylation refers to a reaction of carboxylic acids, removing a carbon atom from a carbon chain. The reverse process, which is t ...
of
pyruvate Pyruvic acid (CH3COCOOH) is the simplest of the alpha-keto acids, with a carboxylic acid and a ketone functional group. Pyruvate, the conjugate base, CH3COCOO−, is an intermediate in several metabolic pathways throughout the cell. Pyruvic aci ...
. The
sensory threshold In psychophysics, sensory threshold is the weakest stimulus that an organism can sense. Unless otherwise indicated, it is usually defined as the weakest stimulus that can be detected half the time, for example, as indicated by a point on a probabi ...
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 Intoxication — or poisoning, especially by an alcoholic or narcotic substance — may refer to: * Substance intoxication: ** Alcohol intoxication ** LSD intoxication ** Toxidrome ** Tobacco intoxication ** Cannabis intoxication ** Cocaine i ...
is also implicated in hangovers.


Acetic acid

Acetic acid Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound with the chemical formula (also written as , , or ). Vinegar is at least 4% acetic acid by volume, making acetic acid the main component ...
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 A by-product or byproduct is a secondary product derived from a production process, 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 consid ...
of fermentation, or due to the spoilage of finished wine. Acetic acid bacteria, such as those from the genera '' Acetobacter'' and ''
Gluconobacter ''Gluconobacter'' is a genus of bacteria in the acetic acid bacteria family. They prefer sugar-rich environments, so are sometimes found as a spoilage organism in beer. They are not known to be pathogenic but can cause rot in apples and pears. ...
'' produce high levels of acetic acid. The
sensory threshold In psychophysics, sensory threshold is the weakest stimulus that an organism can sense. Unless otherwise indicated, it is usually defined as the weakest stimulus that can be detected half the time, for example, as indicated by a point on a probabi ...
for acetic acid in wine 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 Cheval blanc or Cheval-Blanc, French for white horse, may refer to: * Château Cheval Blanc, a wine producer in Saint-Émilion in the Bordeaux wine region of France * Cheval-Blanc, Vaucluse, in southern France ** Canton of Cheval-Blanc * Le Che ...
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'' or '' Kloeckera apiculata''. High levels of ethyl acetate are also produced by lactic acid bacteria and acetic acid bacteria.


Sulfur compounds

Sulfur Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...
is used as an
additive Additive may refer to: Mathematics * Additive function, a function in number theory * Additive map, a function that preserves the addition operation * Additive set-functionn see Sigma additivity * Additive category, a preadditive category with f ...
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

Sulfur dioxide Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic activ ...
is a common wine additive, used for its
antioxidant Antioxidants are compounds that inhibit oxidation, a chemical reaction that can produce free radicals. This can lead to polymerization and other chain reactions. They are frequently added to industrial products, such as fuels and lubricant ...
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

Hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The unde ...
(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 disulfides.


Mercaptans

Mercaptans In organic chemistry, a thiol (; ), or thiol derivative, is any organosulfur compound of the form , where R represents an alkyl or other organic substituent. The functional group itself is referred to as either a thiol group or a sulfhydryl gro ...
(thiols) are produced in wine by the reaction of hydrogen sulfide with other wine components such as ethanol. They can be formed if finished wine is allowed prolonged contact with the lees. This can be prevented by
racking Racking, often referred to as Soutirage or Soutirage traditionnel (meaning racking in French), also filtering or fining, is the process of moving wine or beer from one container to another using gravity rather than a pump, which can be disruptiv ...
the wine. Mercaptans have a very low sensory threshold, around 1.5
μg In the metric system, a microgram or microgramme is a unit of mass equal to one millionth () of a gram. The unit symbol is μg according to the International System of Units (SI); the recommended symbol in the United States and United Kingdom whe ...
/ L,Technical Bulletin - Sulfides in Wine
''etslabs.com'', accessed on 12 March 2006.
with levels above causing ''onion'', ''rubber'', and ''skunk'' type odours. Note that dimethyl disulfide is formed from the oxidation of methyl mercaptan.


Dimethyl sulfide

Dimethyl sulfide Dimethyl sulfide (DMS) or methylthiomethane is an organosulfur compound with the formula (CH3)2S. Dimethyl sulfide is a flammable liquid that boils at and has a characteristic disagreeable odor. It is a component of the smell produced from cook ...
(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''.


Environmental


Cork taint

Cork taint is a wine fault mostly attributed to the compound
2,4,6-trichloroanisole 2,4,6-Trichloroanisole (TCA) is a chemical compound that is a chlorinated derivative of anisole. TCA 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 ...
(TCA), although other compounds such as guaiacol,
geosmin Geosmin ( ) is an irregular sesquiterpenoid, produced from the universal sesquiterpene precursor farnesyl pyrophosphate (also known as farnesyl diphosphate), in a two-step -dependent reaction. Geosmin, along with the irregular monoterpene 2-met ...
, 2-methylisoborneol, 1-octen-3-ol,
1-octen-3-one Oct-1-en-3-one (CH2=CHC(=O)(CH2)4CH3), also known as 1-octen-3-one, is the odorant that is responsible for the typical "metallic" smell of metals and blood coming into contact with skin. Oct-1-en-3-one has a strong metallic mushroom-like odor with ...
, 2,3,4,6-tetrachloroanisole, pentachloroanisole, and 2,4,6-tribromoanisole are also thought to be involved.LaMar, Jim (09/25/02)
Cork Taint
accessed on 12 March 2006.
TCA most likely originates as a
metabolite In biochemistry, a metabolite is an intermediate or end product of metabolism. The term is usually used for small molecules. Metabolites have various functions, including fuel, structure, signaling, stimulatory and inhibitory effects on enzymes, c ...
of
mould A mold () or mould () is one of the structures certain fungi can form. The dust-like, colored appearance of molds is due to the formation of spores containing fungal secondary metabolites. The spores are the dispersal units of the fungi. No ...
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.


Heat damage

Heat damaged wines are often casually referred to as ''cooked'', which suggests how heat can affect a wine. They are also known as maderized wine, from
Madeira wine Madeira is a fortified wine made on the Portuguese Madeira Islands, off the coast of Africa. Madeira is produced in a variety of styles ranging from dry wines which can be consumed on their own, as an apéritif, to sweet wines usually consumed ...
, which is intentionally exposed to heat. 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 expand, and may even push up between the cork and bottle and leak from the top. When opening a bottle of wine, if a trace 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 ultraviolet light, particularly in the range 325 to 450 nm.Drouhin, R.J. (01/23/98
Bottle Glass
accessed 3 April 2006.
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 (DMS) or methylthiomethane is an organosulfur compound with the formula (CH3)2S. Dimethyl sulfide is a flammable liquid that boils at and has a characteristic disagreeable odor. It is a component of the smell produced from cook ...
. 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 (pyrazine) taint

Some insects present in the grapes at harvest inevitably end up in the press and for the most part are inoffensive. Others, notably the
Asian lady beetle ''Harmonia axyridis'' is a large Coccinellidae, lady beetle or ladybug species that is most commonly known as the harlequin, multicoloured Asian, or Asian lady beetle. This is one of the most variable species in the world, with an exceptionally wi ...
, release unpleasant smelling nitrogen heterocycles as a defensive mechanism when disturbed. In sufficient quantities these can affect the wine's odor and taste. With an olfactory detection threshold of a few ppb, the principal active compound is
isopropyl methoxy pyrazine Isopropyl methoxypyrazine (IPMP) is a methoxypyrazine, a class of chemical compounds that produce odors. The odor is rather undesirable and is produced by the Asian lady beetle or by the actinomycete ''Streptomyces'' sp. It can be detected by hum ...
- this molecule is perceived as rancid
peanut butter Peanut butter is a food paste or spread made from ground, dry-roasted peanuts. It commonly contains additional ingredients that modify the taste or texture, such as salt, sweeteners, or emulsifiers. Peanut butter is consumed in many countri ...
, green
bell pepper The bell pepper (also known as paprika, sweet pepper, pepper, or capsicum ) is the fruit of plants in the Grossum Group of the species ''Capsicum annuum''. Cultivars of the plant produce fruits in different colors, including red, yellow, orange ...
, urine, or simply bitter. This is also a naturally occurring compound in Sauvignon grapes and so pyrazine taint has been known to make Rieslings taste like
Sauvignon blanc is a green-skinned grape variety that originates from the Bordeaux region of France. The grape most likely gets its name from the French words ''sauvage'' ("wild") and ''blanc'' ("white") due to its early origins as an indigenous grape in ...
.


Microbiological


''Brettanomyces'' (''Dekkera'')

The yeast '' Brettanomyces'' produces an array of
metabolite In biochemistry, a metabolite is an intermediate or end product of metabolism. The term is usually used for small molecules. Metabolites have various functions, including fuel, structure, signaling, stimulatory and inhibitory effects on enzymes, c ...
s when growing in wine, some of which are volatile phenolic compounds. Together these compounds are often referred to as ''phenolic taint'', ''"Brettanomyces character"'', or simply "Brett". The main constituents are listed below, with their sensory threshold and common sensory descriptors: *
4-ethylphenol Ethylphenol (4-EP) is an organic compound with the formula C2H5C6H4OH. It is one of three isomeric ethylphenols. A white solid, it occurs as an impurity in xylenols and as such is used in the production of some commercial phenolic resins. It is ...
(>140 μg/L): Band-aids, barnyard, horse stable, antiseptic * 4-ethylguaiacol (>600 μg/L): Bacon, spice, cloves, smoky * isovaleric acid: Sweaty, cheese, rancidity


Geosmin

Geosmin Geosmin ( ) is an irregular sesquiterpenoid, produced from the universal sesquiterpene precursor farnesyl pyrophosphate (also known as farnesyl diphosphate), in a two-step -dependent reaction. Geosmin, along with the irregular monoterpene 2-met ...
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 ''Streptomyces'' is the largest genus of Actinomycetota and the type genus of the family Streptomycetaceae. Over 500 species of ''Streptomyces'' bacteria have been described. As with the other Actinomycetota, streptomycetes are gram-positive, ...
'', and
mould A mold () or mould () is one of the structures certain fungi can form. The dust-like, colored appearance of molds is due to the formation of spores containing fungal secondary metabolites. The spores are the dispersal units of the fungi. No ...
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.Kennel, Florence (14/12/05)
Bordeaux boffin solves geosmin conundrum
''Decanter.com'', accessed on 2 April 2006.
The geosmin fault occurs worldwide and has been found in recent vintages of red wines from Beaujolais, Bordeaux,
Burgundy Burgundy (; french: link=no, Bourgogne ) is a historical territory and former administrative region and province of east-central France. The province was once home to the Dukes of Burgundy from the early 11th until the late 15th century. The c ...
and the Loire in France. Geosmin is also thought to be a contributing factor in cork taint.


Lactic acid bacteria

Lactic acid bacteria 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 Effervescence is the escape of gas from an aqueous solution and the foaming or fizzing that results from that release. The word effervescence is derived from the Latin verb ''fervere'' (to boil), preceded by the adverb ''ex''. It has the same li ...
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

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 Acrolein (systematic name: propenal) is the simplest unsaturated aldehyde. It is a colorless liquid with a piercing, acrid smell. The smell of burnt fat (as when cooking oil is heated to its smoke point) is caused by glycerol in the burning fa ...
which reacts with the
anthocyanin Anthocyanins (), also called anthocyans, are water-soluble vacuolar pigments that, depending on their pH, may appear red, purple, blue, or black. In 1835, the German pharmacist Ludwig Clamor Marquart gave the name Anthokyan to a chemical compo ...
s and other phenols present within the wine to form the taint.duToit, M., Pretorius, I.S. (2000). "Microbial spoilage and preservation of wine: Using weapons from nature's own arsenal - A review". South African Journal of Enology and Viticulture 21: 74-96. As red wines contain high levels of anthocyanins they are generally more susceptible.


Diacetyl

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.Gibson, George; Farkas, Mik
Flaws and Faults in Wine
accessed on 12 March 2006.


Geranium taint

Geranium taint, as the name suggests, is a flavour and aroma taint in wine reminiscent of
geranium ''Geranium'' is a genus of 422 species of annual, biennial, and perennial plants that are commonly known as geraniums or cranesbills. They are found throughout the temperate regions of the world and the mountains of the tropics, but mostly in ...
leaves. The compound responsible is '' 2-ethoxyhexa-3,5-diene'', which has a low sensory threshold concentration of 1 ng/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''. As ethanol is necessary for the conversion, the geranium taint is not usually found in
must Must (from the Latin ''vinum mustum'', "young wine") is freshly crushed fruit juice (usually grape juice) that contains the skins, seeds, and stems of the fruit. The solid portion of the must is called pomace and typically makes up 7–23% of t ...
.


Mannitol

Mannitol is a sugar alcohol, and in wine it is produced by
heterofermentative Fermentation is a metabolic process that produces chemical changes in organic substrates through the action of enzymes. In biochemistry, it is narrowly defined as the extraction of energy from carbohydrates in the absence of oxygen. In food ...
lactic acid bacteria, such as '' Lactobacillus brevis'', by the reduction of
fructose Fructose, or fruit sugar, is a Ketose, ketonic monosaccharide, simple sugar found in many plants, where it is often bonded to glucose to form the disaccharide sucrose. It is one of the three dietary monosaccharides, along with glucose and galacto ...
. 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 sugar The subjective sweetness of a wine is determined by the interaction of several factors, including the amount of sugar in the wine, but also the relative levels of alcohol, acids, and tannins. Sugars and alcohol enhance a wine's sweetness, whil ...
s still present. Expert winemakers oftentimes add small amounts of sulfur dioxide during the crushing step to reduce early bacterial growth.


Ropiness

Ropiness is manifested as an increase in 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 dextrins and
polysaccharide Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with wa ...
s by certain lactic acid bacteria, particularly of the genera '' Leuconostoc'' and '' Pediococcus''.


Mousiness

Mousiness is a wine fault most often attributed to ''Brettanomyces'' but can also originate from the lactic acid bacteria '' Lactobacillus brevis'', ''
Lactobacillus fermentum ''Limosilactobacillus fermentum'' is a Gram-positive species in the heterofermentative genus ''Limosilactobacillus.'' It is associated with active dental caries lesions. It is also commonly found in fermenting animal and plant material including ...
'', and '' Lactobacillus hilgardii,'' and hence can occur in malolactic fermentation. The compounds responsible are
lysine Lysine (symbol Lys or K) is an α-amino acid that is a precursor to many proteins. It contains an α-amino group (which is in the protonated form under biological conditions), an α-carboxylic acid group (which is in the deprotonated −C ...
derivatives, mainly; * 2-acetyl-3,4,5,6-tetrahydropyridine * 2-acetyl-1,4,5,6-tetrahydropyridine * 2-ethyltetrahydropyridineMarais, Johan
Flavourful nitrogen containing wine constituents
. ''Wynboer.co.za'', accessed on 12 March 2006.
* 2-acetyl-1-pyrrolene 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,Gawell, Richar
Somellier, A Mouse Must Have Wee'd in My Wine!
''aromadictionary.com'', accessed on 12 March 2006.
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 The subjective sweetness of a wine is determined by the interaction of several factors, including the amount of sugar in the wine, but also the relative levels of alcohol, acids, and tannins. Sugars and alcohol enhance a wine's sweetness, whil ...
present within bottled wine. It occurs when
sweet wines Sweetness is a basic taste most commonly perceived when eating foods rich in sugars. Sweet tastes are generally regarded as pleasurable. In addition to sugars like sucrose, many other chemical compounds are sweet, including aldehydes, ketones, ...
are bottled in non-
sterile Sterile or sterility may refer to: *Asepsis, a state of being free from biological contaminants * Sterile (archaeology), a sediment deposit which contains no evidence of human activity *Sterilization (microbiology), any process that eliminates or ...
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 ''Zygosaccharomyces bailii'' is a species in the genus ''Zygosaccharomyces''. It was initially described as ''Saccharomyces bailii'' by Lindner in 1895, but in 1983 it was reclassified as ''Zygosaccharomyces bailii'' in the work by Barnett et al ...
''. The main issues associated with the fault include turbidity (from yeast
biomass Biomass is plant-based material used as a fuel for heat or electricity production. It can be in the form of wood, wood residues, energy crops, agricultural residues, and waste from industry, farms, and households. Some people use the terms bi ...
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" used to rely on this secondary fermentation in bottle to impart a slight spritziness to the wine, but now usually uses artificial carbonation.


Bunch rots

Organisms responsible for bunch rot of grape berries are filamentous fungi, the most common of these being '' Botrytis cinerea'' (gray mold) However, there are a range of other fungi responsible for the rotting of grapes such as '' Aspergillus'' spp., '' Penicillium'' spp., and fungi found in subtropical climates (e.g., '' Colletotrichum'' spp. (ripe rot) and ''
Greeneria uvicola Grape black rot is a fungal disease caused by an ascomycetous fungus, ''Guignardia bidwellii'', that attacks grape vines during hot and humid weather. “Grape black rot originated in eastern North America, but now occurs in portions of Europe, ...
'' (bitter rot)). A further group more commonly associated with diseases of the vegetative tissues of the vine can also infect grape berries (e.g., Botryosphaeriaceae, ''
Phomopsis viticola Phomopsis cane and leaf spot occurs wherever grapes are grown. Phomopsis cane and leaf spot is more severe in grape-growing regions characterized by a humid temperate climate through the growing season. Crop losses up to 30% have been reported to ...
''). Compounds found in bunch rot affected grapes and wine are typically described as having mushroom, earthy odors and include geosmin, 2-methylisoborneol, 1-octen-3-ol, 2-octen-1-ol,
fenchol Fenchol or 1,3,3-trimethyl-2-norbornanol is a monoterpenoid and an isomer of borneol. It is a colorless or white solid. It occurs widely in nature. The naturally occurring enantiomere (1''R'')-endo-(+)-fenchol is used extensively in perfumery. ...
and
fenchone Fenchone is an organic compound classified as a monoterpenoid and a ketone. It is a colorless oily liquid. It has a structure and an odor similar to those of camphor. Fenchone is a constituent of absinthe and the essential oil of fennel. Fen ...
.Grapevine bunch rots: impacts on wine composition, quality, and potential procedures for the removal of wine faults. Steel CC, Blackman JW and Schmidtke LM, J Agric Food Chem., 5 June 2013, volume 61, issue 22, pp. 5189-5206, .


See also

*
Oenology Oenology (also enology; ) is the science and study of wine and winemaking. Oenology is distinct from viticulture, which is the science of the growing, cultivation, and harvesting of grapes. The English word oenology derives from the Greek word ' ...
*
Acids in wine The acids in wine are an important component in both winemaking and the finished product of wine. They are present in both grapes and wine, having direct influences on the color, balance and taste of the wine as well as the growth and vitality of ...
*
Browning in red wine Oxidation and reduction in red wines can lead to a particularly undesirable brick red color in red wines (or an "orangey" color in white wines). This process is sometimes referred to as browning. In chemical terms, this is called a redox react ...
* Storage of wine


References


External links


Organoleptic defects in wine
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How to Spot Faulty Wine
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in ''Enobytes Wine Online'' {{DEFAULTSORT:Wine Fault Oenology Wine chemistry Wine tasting Product expiration