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Which wines are sealed with corks?
How a wine bottle is sealed influences the ageing and shelf life of the wine after bottling. It depends largely on how much air (and therefore oxygen, which reacts with the sensitive flavours in the wine) can enter the bottle through the closure. The more the wine is exposed to oxygen, the faster it matures - or, in the negative case, degenerates.
The most permeable closure for wine bottles is the cork, which allows around three to four times as much air exchange as other closures. At the same time, cork is one of the oldest types of closure and is also considered to be one of the most environmentally friendly because it is made from a naturally renewable raw material - oak bark.
Corks are traditionally used to seal high-quality wines. These are often Sparkling wines(champagne, sparkling wine) or Red wines with a high tannin content (e.g. from Bordeaux, Piedmont or Rioja), which on the one hand preserves them, but on the other hand requires oxygen to act on the wine in small doses over a longer period of time to make the mouthfeel more pleasant: The tannin molecules join together to form long chains(polymerisation) and thus appear softer and smoother in texture.
However, whether this requires oxygen to be supplied through the cork is scientifically controversial; the widely held view is that the air remaining in the bottle after bottling is sufficient for the wine to continue maturing. In the case of sparkling wine, gas exchange after bottling is even completely undesirable because the wine also loses its carbon dioxide over time. Apart from this, it is now also possible to supply oxygen via closures other than corks.
In this respect, the approach of sealing wines that require ageing with corks is not wrong, but it also harbours some risks. High-quality corks - and using them must be the primary goal - are expensive and only available in limited quantities. Over the course of 20, 30 or more years, which a very high-quality wine can tolerate or even needs to mature, the cork can become brittle and eventually leak, so that it not only lets more and more air into the bottle, but also gradually lets liquid out.
Furthermore, corks - especially those of inferior quality - are the cause of the most common wine defect: cork taint Cork taint. At least three per cent (some estimates even put the figure at ten per cent) of wines sealed with corks have the dull, musty, mouldy smell and dull, bitter taste that are characteristic of this defect. The main cause is the chemical compound trichloroanisole(TCA), which is produced when microorganisms break down certain chlorine-containing substances from wood treatment. The cork industry is making great efforts and constantly developing new methods to render these microorganisms - moulds - harmless, for example by irradiating them with microwaves(dolphin method) or treating them with the enzyme suberase. As a guest in a restaurant, you can immediately complain about a wine with cork taint and have it exchanged; as a customer of the retailer or producer, however, you are dependent on their goodwill when exchanging it.
There are different types of cork:
- Natural corks are cut from the bark of the cork oak. The longer, more elastic and smoother a natural cork is, the better. The surface can be coated (which is usually done today with silicone-rubber mixtures) to increase the seal. A very good natural cork adds up to one euro to the price of a bottle of wine, but is worth the investment. However, natural cork is becoming increasingly rare as it only grows back very slowly and demand remains high.
- agglomerated corks pressed corks are not made from a piece of oak bark, but from cork granulate (ground bark) that is glued together with resin glue. agglomerated corks are significantly cheaper than natural corks. A special form of pressed cork is the DIAM cork.
- Composite corks are agglomerated corks, which have a natural cork disc at the top and bottom ends. This is intended to prevent the glue with which the cork granulate is bonded from chemically and/or aromatically affecting the wine.