Wine Society buyer Toby Morrhall explains how Diam corks are putting an end to cork-induced 'corked' wines and random oxidation.
More and more of our wines are being bottled with Diam corks. These closures look like an ordinary agglomerate cork but appearances in this case are deceptive. Diam have solved two of the greatest problems of the otherwise excellent natural cork: firstly, a fault commonly called 'corkiness', a musty-smelling taint caused when a cork infected with a substance called trichloroanisole (TCA) communicates this to wine, and secondly, the natural variation between different corks in porosity to air, which can lead to extreme variation in the oxidation of wine.
Some producers are using Diam for some or all of their wines. These include Jean-Marc Brocard, Hugel, Louis Jadot, Bouchard Père et Fils and Domaine William Fèvre. We will be switching to Diam corks for Talmard's Mâcon-Villages, The Society's Exhibition Chilean Merlot, The Society's Chilean Merlot, Cabernet Sauvignon and Chardonnay and future bottlings of The Society's Chablis. Members will be able to see if wines are bottled with Diam corks when they click on a product's details on the website.
End of cork-induced 'corked' wines
TCA can be transmitted to wine stored in bulk in wineries from many sources other than corks, particularly from wood used in the construction of wineries and tainted shipping pallets. This explains why traces of TCA can also be found in wines bottled with screwcaps.
But cork has been the chief source of TCA. The Diam process uses supercritical carbon dioxide to remove TCA, a similar process to that used to remove caffeine from coffee beans. It also takes out a whole host of other unwelcome substances in corks which can give rise to such aromas in wine as "dry wood" or "hay".
End of cork-induced random oxidation
There is a small but growing problem of increased permeability of corks to oxygen, described as 'random oxidation'. In affected cases one can open a dozen bottles of the same wine bottled with natural cork, especially some dry white wines (red wines are usually better protected by their tannins, sweet whites by their sugars) and find some bottles in perfect condition, some in all stages of oxidation ranging from a light appley aroma, via nail varnish remover to maderised (smelling of Madeira or Sherry).
Whilst this phenomenon of random oxidation can be caused by various problems – for example, a bottle with a neck diameter outside given tolerance levels, a faulty filler head, or differences in the free SO² level in the vats feeding the bottling line and insufficient protection by inert gas – a chief cause appears to be the variable porosity of corks to air.
Low porosity corks are superb closures, but cork is a natural product and so is variable. Currently cork quality is assessed only by a visual examination which cannot ascertain a cork's internal structure or porosity. Thus even a batch of the most expensive corks may contain some individual corks which are excessively porous to air.
The Diam process chops cork into pieces and sorts the superior, highly elastic, suberin component from the less elastic lignin, which is discarded. It mixes the suberin with microscopic spheres of the same substance used for contact lenses, which fills the voids between the cork particles reducing porosity to air and increasing elasticity without introducing humidity. Finally the pieces are mixed with a glue and moulded under pressure. The mechanical properties of the cork are guaranteed for a certain minimum number of years depending on the grade of cork – Diam 2, 3, 5 and 10.
Adoption of Diam c
The take-up of Diam corks is growing quickly, particularly for white Burgundy, which can be affected by random oxidation. Sadly, it is often not yet used on the grands crus with the longest potential lives, because of a lack of track record. Diam 5 has been in production for eight years and eight-year-old corks are still performing very well. The newer Diam 10 was introduced about 18 months ago. Given the current risk with natural cork, I am encouraging many of our suppliers to use Diam 5 and 10.