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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)

Name (also corker, cork taste, cork) for a dreaded wine faults, In Austria this is colloquially also with "the wine stoppelt" (Stoppel = corks) described. It manifests itself by musty, musty and chemical smell of wet, rotting wood or leather. The odor is sometimes called earthy described, what the alcohol geosmin is involved. The taste is uncomfortable bitter and astringent, Often the error can only be perceived by smell. A typical feature is lacking Fruchtighkeit or a partially or completely covered varietal of the wine.

Korkschmecker - glass with cork and TCA molecule

The unpleasant leaving the taste lasts for a long time. At a higher wine temperature The symptoms are even more obvious. For red wine is the Perceptual threshold through the overlapping ones tannins a bit higher, the error may not be perceived so strongly here. The main cause of "genuine cork treats" is the chemical trichloroanisole (TCA), the exact chemical name is 2,4,6-trichloroanisole. This was first proved in 1981 by Prof. H. Tanner at the Swiss Federal Research Institute in Wädenswil (Switzerland). This substance is produced by microbial methylation of trichlorophenol (TCP). That is, by microorganisms like molds the TCP is converted to TCA. Australia became the stuff in 2004 Methoxy-dimethylpyrazine isolated, which is the second cause.

causes

Although TCA usually enters the wine via 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 provides the reason that the cork problem is neglected or at worst considered insignificant. Still in the 1990s it was customary in cork production to bleach and sterilize the bark with substances containing chlorine. This has been changed over by most cork-producing countries, today it is with 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 (for example, caused 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 in the winemaking respectively. In Europe, however, it is no longer possible to use plant protection products that could serve as precursors for TCA formation. In France, many Châteaux are currently renovating trusses and, in general, wooden beams impregnated with wood preservatives (TCP, other chlorophenols). These can evaporate and then enter the cellar atmosphere and from there into the wine. It is also possible to add up all chlorine sources.

perception

A phenomenon is that not all people have the ability to perceive, or at least have a diminished ability. A trained and sensitive taster can already absorb a few billionths of a gram (1 nanogram = 0.000000001 g), but in less experienced people this can be above 30 ng. Korkschmecker can appear very clearly or even very hidden, so that they are barely noticeable. In this case, they are aptly called a "cork crawler" (English: fruit scalping). in the White wine will be 1 ng, im red wine 5 ng TCA per liter as an odor Perceptual threshold considered. In the water this is still considerably higher, here the perception threshold can lie with 200 ng per liter. The problem is that, in addition to trichloroanisole, there are a number of similar chemical compounds that cause a similar odor or taste in the wine. One of them is tribromoanisole (TBA).

At the Wädenswil Institute in Switzerland, Cadine, Geosmine, Methyls, octanes and pyrazines, of which there are ten or more subvariants of some of them. The human sense of smell is generally not very selective, so that in the presence of two or more musty compounds, additive effects are possible and even very likely in the untrained. Also the two wine mistakes Schimmel taste and barrel taste smell pretty similar. But today these mistakes rarely occur anymore. The doctrine is that the substance TCA is the main cause of the "real cork treats". Whether TCA sensory is always 100% recognized, is the question. Undoubtedly, this is only by chemical analyzes possible.

detection methods

Thanks to a newly developed sensor, the molecule 2,4,6-trichloraniosol responsible for the corkscrew can be quickly and clearly detected in the wine. The test procedure was developed in Switzerland at the University of Friborg in collaboration with the University of Bordeaux. By means of a sponge-like, porous supramolecular network, the corkscrew molecules can be "captured" as it were. Once a TCA substance is present and has settled in the pore of the sensor, there is an optical signal. The sensor can be regenerated and then ready for new measurements.

Occurrence (affected wine quantity)

Significant amounts of world wine production are at least adversely affected by the cork taint, at least in the worst case completely inedible. However, the estimates of the error rate vary considerably. In most sources, however, it is assumed that at least three percent of faulty bottles coincide. Often, however, is spoken by quantities to 10% and some experts estimate the proportion even up to 15% and even higher. However, even at "only" three percent this would be an unbelievable amount of about a billion (that's a thousand million) bottles a year that are inedible by this wine error.

solutions

Meanwhile, there are some approaches to cork production. Either you kill the mold fungi by radiation or heating the cork slices with microwaves (see dolphin ), or one inactivates the metabolic products of the molds (anisols and phenols) by the enzyme Suberase, This procedure was in the institute Geisenheim developed and used since 1999 in Portugal. However, a hundred percent solution does not seem to have been found yet. In the meantime, a worldwide practice is the use of alternative closures such as screw cap or glass corks,

Picture left: by Adriano Gadini on Pixabay
Picture right: By Quasar Jarosz in Wikipedia , CC BY-SA 3.0 , Link
Source verification method: The Winzer 06/2019

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