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corked

gosto a rolha (PO)
sapore di tappo (I)
goût de bouchon, bouchonné (F)
sabor a corcho (ES)
cork taint, cork taste, corky taste (GB)

Term (also cork, cork taste, corkton) for a dreaded wine faults, In Austria this is colloquially described as "the wine stubbles" (stubble = cork). It is expressed by a musty, musty and chemical smell of wet, rotting wood or leather. The odor is sometimes called earthy described what the alcohol type geosmin is involved. The taste is uncomfortable bitter and astringent, Often, however, the error can only be perceived by smell. A typical indicator is lack Fruchtighkeit or a partially or completely covered one varietal of the wine.

Korkschmecker - glass with cork and TCA molecule

The uncomfortable leaving the taste lasts a long time. At a higher one wine temperature the symptoms become even more apparent. With red wine it is Perceptual threshold through the overlapping tannins somewhat higher, the error may not be perceived as strongly here. The main cause of the "real cork taster" is the chemical substance trichloroanisole (TCA), the exact chemical name is 2,4,6-trichloroanisole. This was first demonstrated in 1981 by Prof. H. Tanner at the Swiss Federal Research Institute in Wädenswil (Switzerland). This substance is created by microbial methylation of trichlorophenol (TCP). That means that through microorganisms like molds the TCP is converted to TCA. In 2004 the fabric was made in Australia Methoxy-dimethylpyrazine isolated, which is considered the second cause.

causes

Although TCA mostly reaches the wine through the cork, it is by no means cork-specific, but the starting material TCP can come from many sources, which makes it difficult to determine the cause. Unfortunately, this also offers the reason that the cork problem is minimized or, in the worst case, is considered immaterial. In the 1990s it was still common in cork production to bleach and sterilize the bark with chlorine-containing substances. This has been changed by most of the cork producing countries, today it is used hydrogen peroxide worked. Another cause is the inadmissible preservation of corks and barrels with the toxic wood preservative PCP (pentachlorophenol).

Likewise, chlorine-containing substances can be caused by polluted rainwater (e.g. triggered by bush or forest fires and industrial air pollution), by the use of pesticides in the vineyard and by the use of chlorine-containing substances at the winemaking respectively. In Europe, however, pesticides that could serve as precursors to TCA formation may no longer be used. In France, many Châteaux roof trusses and generally wooden beams that are impregnated with wood preservatives (TCP, other chlorophenols) are currently being renovated. These can evaporate and then get into the cellar atmosphere and from there into the wine. A summation of all chlorine sources is also possible.

perception

A phenomenon is that not all people have the ability to perceive, or at least have a reduced ability. A trained and sensitive taster can already perceive a few billionths of a gram (1 nanogram = 0.000000001 g), but with less experienced users this can be above 30 ng. Cork tasters can appear very clearly or even very hidden, so that they are hardly noticeable. In this case, they are aptly referred to as "fruit scalping". in the White wine becomes 1 ng, in red wine 5 ng TCA per liter as odor Perceptual threshold considered. In the water this is considerably higher, here the perception threshold can be 200 ng per liter. The problem is that besides trichloroanisole there are a number of similar chemical compounds that cause a similar smell or taste in the wine. One of them is tribromoanisole (TBA).

At the Wädenswil Institute in Switzerland, Cadine, Geosmine, Methyls, octanes and pyrazines, some of which have ten or more sub-variants. The human sense of smell is generally not very selective, so additive effects are possible in the presence of two or more musty compounds and even very likely inexperienced. Also the two wine mistakes Schimmel taste and barrel taste smell pretty similar. These mistakes are rare nowadays. As a doctrine, the substance TCA is the main cause of the "real cork taster". Whether TCA sensory the question is always 100% recognized. This is only beyond doubt through chemical analyzes possible.

detection methods

Using a newly developed sensor, the 2,4,6-trichloroaniosol molecule responsible for cork tasting can be quickly and clearly detected in wine. The test procedure was developed in Switzerland at the University of Friborg in collaboration with the University of Bordeaux. Using a sponge-like, porous supramolecular network, the cork taster molecules can be “captured”, so to speak. As soon as a TCA substance is present and has nested in the pore of the sensor, there is an optical signal. The sensor can be regenerated and is then ready for new measurements.

Occurrence (quantity of wine affected)

Considerable amounts of worldwide wine production are at least negatively affected by the cork taster, or in the worst case, completely inedible. However, estimates of the error rate vary considerably. Most sources, however, consistently assume at least three percent defective bottles. However, quantities of up to 10% are often spoken of and some experts estimate the proportion as high as 15% and even higher. Even with “only” three percent, however, this would be an unbelievable amount of around one billion (that's a thousand million) bottles a year , which are inedible due to this wine error.

solutions

In the meantime, there are a few solutions for cork production. Either you kill the mold germs by radiation or by heating the cork discs with microwaves (see below dolphin ) or you inactivate the metabolic products of the mold (anisols and phenols) by the enzyme Suberase, This procedure was in the institute Geisenheim developed and used in Portugal since 1999. However, a 100 percent solution does not yet seem to have been found. In the meantime, a worldwide practice is the use of alternative ones closures such as screw cap or glass corks,

Left: by Adriano Gadini from Pixabay
Right: By Quasar Jarosz at Wikipedia , CC BY-SA 3.0 , link
Source of verification: The winegrower 06/2019

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