John Hale, of Dunedin, asks :-

Once upon a time wine bottles had corks, now more often they have screwcaps. With corks, the wine was sometimes "corked." What is "corked", and can it be cured or avoided?

Bernard Newman, a wine scientist at Lincoln University, responded.

The ‘corked’ (or cork taint) wine effect is eliminated by a screw cap closure. This is why screw caps have become so popular in recent years.

The taint occurs when the chlorine used to bleach sheets of cork reacts with even the tiniest amount of mould that may be present in that cork. A chemical called trichloranisole (or TCA for short) is made by this combination of mould + chlorine. Humans are able to smell this chemical in the smallest amounts – even just a few parts per trillion!

Corks can even pick up taints from their surroundings and these can be slowly transferred through the cork and into the wine. The frustration for the winery, the bottle store and the consumer is that cork taint is quite random and cannot be detected by any means other than opening a bottle and trying the wine.

Once a wine is tainted, it cannot be cured/fixed. The frustrating thing is that cork taint can range from being very subtle and barely noticeable through to quite shocking. It is the subtle changes that are the most frustrating as only experts will notice these, the average drinker may think the wine uninteresting or disappointing and not suspect the problem unless they have had the wine before/after from a bottle with an uncontaminated cork.

If a bottle is to have a cork, the taint can be avoided most effectively by using a manufactured cork. There is a process where cork sheets are chopped into little crumbs by a machine and all traces of mould and chlorine can then be removed in a complicated vacuuming type process. The cork is then put back together using a gluing process to give what is generally regarded as a taint free cork. You can quite easily tell this type of cork as you can see it is made up from lots of small pieces.