Devil in corks: Understanding a corked wine

A good proportion of wines are bottled with cork stoppers although a few countries, such as Austria, Australia and New Zealand, have switched almost entirely to screwcaps. All the same, most of the world still use corks for red wines. In some large markets, such as China, selling screwcap products is unthinkable.

Corks are taken for granted but they can sometimes cause trouble. The biggest problem far is when a wine becomes corked or “ corky “.

What does this mean?

In vast majority “ corkiness “ is NOT a fault of wine itself but corks are to be blamed.  

Cork stoppers are made from the bark of an evergreen tree commonly called the cork oak ( Quercus suber ). Like all living organisms, the cork oak can be affected by pests. These mainly parasitic fibrous fungi live in its bark. The fungi may produce a special chemical substance called 2,4,6-Trichloroanisole, or TCA for short. If present, this would impart a penetrating “ corky “ odour which completely would taint the wine in the bottle. Unfortunately, it is impossible to get rid of the “ corkiness “ entirely. Statistically up to 1.5% of manufactured corks are affected with TCA in spite of the best efforts of large producers to reduce the rate of its occurrence.

How could these problems dealt with?

Around 95% of the world’s corks come from Portugal.

The bark of the cork oak provides the raw material. A mature oak can be harvested every six to eight years.

The thickness of the bark determines the size of the corks that can be made from it.

The harvesters watch out for the tell-tale yellow patch typical of the fungal infection in the bark. If they find one, the bark is immediately separated and burnt later.

The harvested cork needs to dry for years.

Before processing the cork is steamed at high pressure to kill any harmful microorganisms that may be present.

Then the bark is cut into smaller pieces and the corks are made with a hole puncher.

Although the raw material is being checked continuously from bark harvest through processing it is virtually impossible to filter out infected cork with 100% effectivity. Whereas the infection rate of 2 -4% from ten years ago has now decreased to 1.5% due to the strenuous efforts of the cork makers it is still not negligible… 

In order to reduce the statistical probability that flawed corks would occur in a higher percentage in any particular batch the finished corks of similar size and quantity are mixed several times before they are shipped

In cases of cork faults usually the winemakers take the blame. This does not seem fair because 1. Cork stoppers are demanded by the market not the wine producers 2. Wineries spend 4-5 times more money ( in advance )  purchasing the best quality corks instead of using reliable reasonably priced screwcaps 3. Winemakers are responsible for many things but for undetected natural processes in faraway cork factories.

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