The Problem with Cork

Posted by Michael Hutton on

Cork has a long history in the wine world – used by the Greeks and Romans going back to the 5th Century BC – but then largely abandoned through the dark ages and not ‘rediscovered’ as a reliable way of sealing wines until the 17th Century.

Why Cork & What Is It?

Cork is essentially the bark from the cork tree, a form of evergreen oak grown through Portugal and Spain, and to a lesser extent in Northern Africa and Italy.  Harvesting the bark from the tree requires expertise to avoid damaging the tree itself- unlike most trees that will die if the bark is removed, a spongy outer layer of dead bark from the cork tree will slowly regenerate – the first harvest of cork comes at about 25 years old, though this and the second harvest are not of sufficient quality to use for corks (usually used for cork flooring instead!).  Over the course of its lifespan a cork tree can be harvested over a dozen times.

The material in itself is miraculous as it is unique- it is light, highly resistant to moisture penetration, flexible, resistant to temperature changes and has a great ability to form a ‘suction’ effect on glass… making it virtually ideal as a seal for fine wine.  It is not completely air-tight, and will let tiny amounts of air through millions of small holes to allow a wine to age gracefully over time. 

The Problems with Cork

Lying the wine bottle on its side keeps the cork moist – if allowed to dry out it becomes brittle and allows too much oxygen through a wine will spoil more quickly.  Too much variation in temperature and the cork will expand and contract, again letting through too much air and a wine will prematurely age (and not in a good way).  Too much humidity and the cork will go mouldy and disintegrate. 

Perhaps the worst curse of the wine world is Cork Taint – Tricholoanisole or ‘TCA’ – tiny amounts of mould in the cork that ruin the wine.  Humans are particularly sensitive to it, detecting it in as little as 5 parts per trillion. 

A wine suffering from very small amounts of Cork Taint may not be detectable, and perhaps only noticeable in direct comparison with a non-corked wine of the same kind – usually coming across as a touch dull and less flavourful.  A badly corked wine on the other hand will smell and taste like a wet dog rolled in old newspaper – very unpleasant – and is the reason why traditionally at a restaurant the waiter will pour a small taste from the bottle for inspection.

If your wine is “Corked” – take it back to where you bought it.  You’d send it back if it were spoiled at a restaurant, and any decent retailer should replace or refund a corked wine when accompanied by the receipt.  Don’t be offended if they check the wine, some wines are supposed to taste a bit musky and dirty, and aren’t corked at all (examples include some South African Pinotage, French Burgundy, and a number of Chilean reds). 

Different Kinds of Corks

Besides ‘Natural’ Corks, there are a range of alternatives used as substitutes:

  • Agglomerated cork is a moulded cork from 50% synthetic glue and 50% granulated cork.  The chemicals used in bonding the cork will break down over time, and is not recommended for long lived cellaring.
  • Natural Disk Top cork (also called “twin-topped” or “1+1” cork) – where an agglomerated or granulated cork is capped at each end by a small “disc” of natural cork - made of 40% granulated cork, 10% natural cork, and 50% synthetic glue. 
  • Colmated Cork – where a lower grade cork is infused with cork dust and glue to improve its performance and consists of 90% cork, 10% cork dust and natural glue.

None of these are seen as performing as well as a proper natural cork, especially for a top quality wine.  In NZ we tend to see a special kind of cork used: the DIAM Cork which is made by finely grinding natural cork, blasting it with a high temperature liquid carbon dioxide to wipe out the compounds that create cork taint, and reconstituted with a polyurethane type glue to bind it together.  This looks a lot like a cheaper Agglomerated cork, but supposedly has a 30-year lifespan making it a good solution for higher end and longer lived wines, without the risk of cork taint.

While 2/3 of wine is still sealed under cork, other alternatives include the Stelvin Screwcap and in Germany and Austria increasing numbers of glass stoppers.

Regional Variations

European wine producers (and consumers) doggedly persist in using cork as a strong preference over screw caps – not so in NZ and Australia where over 95% of wine is now sealed with the Stelvin Screw Cap.  Depending on who you talk to, the level of Cork Taint from natural cork can be 1 in 100 for a high quality cork, but degrades to 1 in 20 or even as high as 1 in 8 bottles for poor cork – an unacceptable failure rate for any modern consumer good! 

There’s also not enough of it - given the relatively small geographical area that produces decent cork (experiments in growing cork in the Americas, Japan and Russia have been disappointing) there isn’t enough to support the ever increasing world supply of wine. 

We find significant variation in the levels of cork taint by country – French wines (especially the better ones) tend to be reliably good.  Italian wines on the other hand in our experience have significantly higher “failure” rates.  Perhaps the inexpensive Italian wines economise on lower quality “corks”, and maybe this is a reason why we see increasing levels of synthetic corks made from plastic or Styrofoam-type materials in the cheap & cheerful Italians.  Most New Zealand producers using cork use a “DIAM” cork.

Does it Taste any different?

Some people say that wines tasted with anything other than a proper natural cork taste different.  Criticism of some of the cheap agglomerated corks include the wine tasting a bit of glue, while others say that screw-cap wines tend to have a duller aroma and flavour.  Is this an acceptable price to pay to eliminate the crushing disappointment of a highly anticipated wine ruined by cork taint?

A handful of the French wines that we are importing we will get the same wine sealed under both screw cap and cork… and I sense a blind tasting coming up!

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