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Merum: A few weeks ago, Paul Pontallier from Château Margaux was thinking about possibly equipping his second wine, Pavillon Rouge, with a screw cap soon. Will the screw cap continue to replace the natural cork in the next few years?

Jung: I don't think the screw cap will ever completely replace the natural cork. Winegrowers will continue to use natural cork, especially for high-quality wines, because it has very special physical properties that make it good for sealing bottles. Another advantage is its naturalness. It is made of an ecologically valuable raw material that is no longer used as it was many years ago when it had a kind of monopoly.

Merum: Cork proponents argue that thanks to hygiene and the latest techniques, the TCA problem is getting better and better under control. Is that true? Have bottles with cork defects decreased noticeably in recent years?

Jung: In the past, any cork material was used to make bottle caps, even the lowest quality. Today, thanks to the many alternatives, not all cork batches are needed for bottle cork production. Among other things, this has led to a general improvement in the quality of natural corks.

The problem of cork taint has actually decreased significantly in recent years. If you use a good natural cork and have no problems with it, you don't necessarily have to look for an alternative. In Geisenheim, by the way, we are currently looking into where dull, musty off-flavours come from that do not come from natural cork. TCA (trichloroanisole) is formed by moulds and can occur anywhere where there is moisture. In tests with alternative closures, some wines nevertheless showed musty tones and cork tastes.

After getting to the bottom of things, we were able to identify the sources. Among other things, it was contaminated seals, dirty hoses, mouldy wooden pallets. This is an immense problem in many wineries.

Merum: Why do you think winemakers in France, Italy and Spain have such a hard time with the screw cap?

Jung: That is a question of mentality. These countries are much more attached to their traditions and are less volatile when it comes to such decisions. Take the Austrians, on the other hand, who moved away from natural cork in an extreme way, first to plastic stoppers and now to screw caps. German winemakers are flexible with their closures, but the topic is hotly debated and there is still a lot of uncertainty.

Merum: How do you explain the fact that so many wines are still sealed with inferior agglomerate corks or two-disc corks?

Jung: It is a pity that many winegrowers still resort to inferior corks, especially because with agglomerated corks it is usually not just one bottle that is affected, but a whole batch. This can quickly amount to hundreds of bottles contaminated with bad corks. Many wineries shy away from the investments that a conversion to rotary corks entails. Sometimes it is very difficult to convince the winegrowers.

But some producers also want to stay with natural cork for ecological reasons, since aluminium production is very energy-intensive. The processing of the aluminium for the screw caps is a big environmental burden. I myself think the screw cap is very good, it works wonderfully, but it is certainly not ideal in every respect.

Professor Dr. Rainer Jung has been deputy head of the Department of Cellar Management at the Geisenheim Research Institute since 2005. He studied viticulture and oenology in Geisenheim and Gießen and did his doctorate on "Examination methods for describing cork quality". He has been working at the Geisenheim Research Institute since 1995. (Photo: Merum)

Merum: What does the winegrower have to pay attention to before or during bottling if he wants to use a screw cap?

Jung: First and foremost, he has to be aware that this gives him more headspace, which means he has more oxygen in the bottle. He has to think about what to do with this headspace.

Many inertise the space with carbon dioxide, which does not affect the wine quality because the quantities are so small. The winemaker also needs to know that with a screw cap, less oxygen gets to the wine during storage. In most cases, he therefore adds less SO2 (sulphur dioxide) during bottling than with a wine sealed with natural cork.

Especially with red wines, many winemakers also work with micro-oxidation, which means that they already prepare the wine for bottling with the screw cap during vinification. The wines that are screw-capped will certainly develop differently, they mature more slowly than those with natural cork.

Merum: For which wines would you use screw caps? Are there wines for which you would prefer to use natural corks?

Jung: I would use the screw cap for fresh white and also rosé wines, i.e. for wines that are consumed relatively young, even though screw caps are definitely also suitable for a longer storage period. In Geisenheim, for example, we have been storing our experimental wines with screw caps since the 1970s because we do not accept any variations that could come from the cork.

The disadvantage of natural cork, apart from the risk of cork taste, is that there are big differences in wine development from bottle to bottle. As a winegrower, you have to accept these fluctuations when using natural cork. You don't have this worry with screw caps, because the wine quality remains constant.

In the end, it is often an image decision that the winegrower makes. In Württemberg, where they started working with screw caps relatively early, the winegrowers initially only used them on the 1-litre bottles to see how consumers would react. Very quickly, the screw cap had a "cheap image". In the meantime, this has changed somewhat in Germany thanks to a number of young winemakers who also use screw caps for high qualities.

Merum: Is there a perfect closure for all types of wine?

Jung: No, there is not. Every closure has its advantages and disadvantages. For example, I have had good experiences with DIAM, a cork made of fine granulate that is cleaned with supercritical carbon dioxide. This process is also known from the decaffeination of coffee. For me, the DIAM cork is a good combination of renewable raw material and modern technology.

90 percent of all wines that come onto the market today are drunk within two years. Actually, any closure is suitable for this storage period. But there is always discussion about the remaining ten per cent. Natural and glass corks as well as screw caps are suitable for longer storage. And then the question is often not which technical closure is the best, but which is the most image-boosting closure and which best suits the wine and the winery. It goes without saying that one should always look for the best quality in any decision.

The wine is most at risk from low-quality agglomerated corks, which are made of waste products with glue. There, the danger is great that the wine will taste of both TCA and a plastic clay caused by the glue. With high-quality natural corks, there are fewer and fewer failures. Crown corks seal similarly well as screw caps, but have an even worse image among consumers. The Vino-Lok is much more expensive compared to the other closures. Therefore, it has a very small market share.

To the magazine article "Screw tops are becoming socially acceptable"

To the magazine article "The most common closures

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