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The oak cork and the wine bottle are breaking up

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June 9, 2011

The anticipation created by the popping cork of a fine vintage, perhaps the treasure of one’s cellar, turns into sour disappointment seven times for every hundred bottles sold of the same batch (Álvarez-Rodríguez and others 2002). The wine in question presents a mouldy aroma, with a tinge of gym socks – what some people describe as “wet cardboard”. This anomaly is known as “cork taint”, revealing the implicated culprit – the historical partner to wine. The gradual divorce between the oak cork and the wine bottle can be seen in increasing amounts of wines with synthetic corks or screw top closures (Lopes and others 2007).

There are three things to consider in the wine closure situation. The first takes on the form of wine’s arch-nemesis, oxygen, which combines with the alcohol in wine to produce acetylaldehyde, the major chemical component of vinegar (Lopes and others 2007). The second thing to consider is the opposite of the first, in which over-enthusiastic exclusion of oxygen from wine bottles results in a sulphurous off-flavour, known as “reductive character” (smalloak.com n.d.). The third thing to keep in mind is the fact that began this whole debate in the first place: the ‘cork taint’, which is caused primarily by a chemical known as 2,4,6-trichloroanisol (Vlachos and others 2007).

Traditional wine corks are produced from the species of oak tree, Quercus suber (Ezquerro and Tena 2005). The properties of oak cork that have concretized its role in wine closures include its chemically inert nature and the flexibility of the material, enabling re-corking whereupon the cork expands to create a good barrier between oxygen and wine. Oak cork contains miniscule pores within its structure that contain oxygen from the atmosphere. This small amount of oxygen in the cork is allowed a slow entrance into the bottle, which is believed to produce a better wine, particularly in fine wines that are intended for aging (Lopes and others 2007). One of the problems is that oak cork is a natural product, thus performance is highly variable in terms of the entrance of oxygen, producing wines of differing quality. In regards to cork taint, the primary culprit, 2,4,6-trichloroanisol, is produced by fungi naturally present within the cork, which degrade the cork material to use as sustanence (Álvarez-Rodríguez and others 2002).

Synthetic corks are composed of plastic and, in some cases, combined with reconstituted cork particles. These corks are entirely man-made; thus, their quality can be controlled to ensure a consistency in the quality of the wines. The fungi responsible for cork taint would not be able to colonize synthetic corks for the lack of suitable nutritive material, thus eliminating the problem of cork taint. However, it has been observed by the wine community at large, and concluded in a study by Lopes and others (2007), that synthetic closures allow the entrance of relatively large amounts of oxygen from the atmosphere, rendering these types of corks suitable only for wines that must be immediately consumed and useless for wines that need aging. This is due to the current inability to produce synthetic corks that equal natural corks in their flexibility, resulting in inferior sealing and re-corking ability (Lopes and others 2007).

A more recently introduced wine closure is the screw top closure, similar to those found on beer bottles. This form of wine closure is heralded as the replacement of the cork, evidenced in such movements as the New Zealand Screwcap Initiative, where bottle opening will be achieved with the flick of the wrist instead of the traditional tug-and-pop. Metal closures provide a better barrier between the wine and oxygen, allowing for a truly consistent product overall (Garcia and others 2007). There is no possibility for cork taint in this case because these closures are not corks at all. There is currently insufficient data on the use of metal closures on wines intended for aging, due to the belief that a little oxygen is necessary for wine maturation. Some wine producers argue that there is sufficient oxygen within the bottle to allow for satisfactory character development (Garcia and others 2007). Insufficient oxygen, which is more likely with screw caps than when involving natural or synthetic cork, can result in reductive character (smalloak.com n.d.).

The age-old practice of wine-drinking has resulted in a deeply rooted culture that is fond of its traditional practices. The proposition of any changes to the ritual encounters protests from purists in the wine community. The discerning, wine-loving consumer of today should have some insight into this ongoing closure debate, taking into consideration his purpose of the purchase (for aging or immediate consumption) as well as the known advantages and disadvantages of existing wine closures in the market. The acquisition of this closure repartee will ensure the absence of consumer sentimentality in determining the direction of the oenological future.

References

Álvarez-Rodríguez ML, López-Ocaña L, López-Coronado JM, Rodríguez E, Martínez MJ, Larriba G, Coque JR. 2002. Cork taint of wines: role of the filamentous fungi isolated from cork in the formation of 2,4,6-trichloroanisole by o-methylation of 2,4,6-trichlorophenol. Appl Environ Microbiol. 68(12): 5860–5869.

Ezquerro O, Tena MT. 2005. Determination of odour-causing volatile organic compounds in cork stoppers by multiple headspace solid-phase microextraction. Journal of Chromatography A 1068: 201–208.

Garcia R, Bardhi F, Friedrich C. 2007. Overcoming consumer resistance to innovation. MIT-Sloan Management Review 48(4): 82-88.

Lopes P, Saucier CD, Teissedre PL, Glories Y. 2007. Main routes of oxygen ingress through different closures into wine bottles. J. Agric. Food Chem. 55: 5167-5170.

smalloak.com. n.d. The use of inert gas in the wine making process. Retrieved on February 4th 2008 from: http://www.smalloak.com/papers/inertgas/inertgas.html

Vlachos P, Kampioti A, Kornaros M, Lyberatos G. 2007. Development and evaluation of alternative processes for sterilization and deodorization of cork barks and natural cork stoppers. Eur Food Res Technol 225:653–663.


SUMMARY


The anticipation created by the popping cork of a fine vintage, perhaps the treasure of one’s cellar, turns into sour disappointment seven times for every hundred bottles sold of the same batch (Álvarez-Rodríguez and others 2002). The wine in question presents a mouldy aroma, with a tinge of gym socks – what some people describe as “wet cardboard”. This anomaly is known as “cork taint”, revealing the implicated culprit – the historical partner to wine. The gradual divorce between the oak cork and the wine bottle can be seen in increasing amounts of wines with synthetic corks or screw top closures (Lopes and others 2007). 

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