Corks versus Screwcaps – Does it Matter?

This update of a 2015 Carl’s Corner was prompted by a recent article by Dave Green in WineMaker Magazine, Virtual Edition,  For nearly two centuries, cork has been the preferred closure for wine bottles.  Cork is a natural product cut from the bark of a cork oak tree that is flexible and only a tiny bit porous.  By properly shaping a cork to fit snugly inside the neck of a wine bottle, one can produce a very sturdy, long-lived stopper that is almost impervious to air intrusion.  So, what is wrong with having cork closures for wine bottles, and why have screwcaps become more common and more popular?

There are basically two major issues with cork closures.  One is simply that a special tool, a corkscrew, is needed to open the wine.  Many people are intimidated by a corkscrew and have never become truly adept at using one.  Many variations on the basic corkscrew have been invented, and some are actually quite handy.  However, the fact remains that one still needs a special tool to remove the cork from a wine bottle.  With screwcaps, opening a wine bottle is very, very simple and no tools, other than your hands, are needed.  (See previous Carl’s Corner on Corkscrews, Mar-2017)

The second issue with cork closures is the potential for what is called “cork taint.”  You will often hear this described as “corked” wine, and it is a terrible flaw that often renders a wine undrinkable.  Cork taint is caused by the development of a chemical compound called 2,4,6-trichloroanisole (TCA, for short) that smells like wet, moldy cardboard or newspaper in a damp basement, or like sweaty, moldy socks stored in a gym bag in the trunk of a car for a week in summer heat.  YUK!  The problem with TCA is that it is detectable by the human nose in the low parts-per-billion range, and the smell overwhelms any of the fruity, delightful aromas that a wine might otherwise offer.  Thus, a wine that is corked, or has developed cork taint, while maybe drinkable, is certainly not enjoyable. 

How does cork taint form?  There are natural bacteria in cork that can combine phenolic compounds in wine with chlorine, a chemical ubiquitous in our modern world.  Years ago, chlorine bleach was used to lighten the color of wine corks, providing ample chlorine for the formation of TCA.  As late as 25-30 years ago, almost 1 bottle of every 10 suffered some level of cork taint.  New bleaching technology (primarily using ozone), and better water treatment techniques (not using chlorine) have vastly reduced the amount of chlorine available to produce TCA.  It is estimated that today only 1 bottle of every 75-100 suffers from some measure of cork taint. 

Cork quality has improved over the years as better production, sterilization, and TCA detection methods have been developed.  In addition to natural corks cut directly from the bark, composite or agglomerated corks are molded from small particles of cork leftover from manufacturing.  These composite corks are less expensive, work well, and have become very popular with winemakers.  Synthetic corks molded from a range of polymeric materials are also available, but seem to have fallen out of favor these days. 

With screwcaps, there is no potential for cork taint.  So, you may ask, why aren’t all wines closed with screwcaps?  First, there is the impression that only “cheap” wines have screwcaps.  Many producers want to maintain the impression that their wines are high quality, and corks are still considered the preferred high-quality bottle stoppers.  Another issue is the long-held belief that the natural porosity of cork allows very slow exchange of air into the wine bottle, enabling wine to develop special secondary flavors (mature) over time.  This may or may not be totally true, depending on which expert is consulted, but probably the most important point is that unless the consumer is aging wine for years in a climate-controlled cellar, most wines will never stay around long enough to undergo this slow interaction with air to gain those special mature flavors. 

Detailed, technical scientific studies have been done and are still continuing to compare the potential for proper aging with screwcaps vs. corks.  The results, so far, suggest that the flexible liner composition used in screwcaps to make a liquid-tight seal, can be adjusted to allow a tiny amount of air intrusion over time as fine wines age, much like that with corks.  A number of top wineries in the world are experimenting with corks vs. screwcaps, and their results will someday determine whether screwcaps become the fine wine closure of choice. 

For us, today, the important thing to recognize is that for a vast majority of wines, the type of closure really doesn’t matter.  And, it certainly does not indicate a relative level of quality.  Great wine can be sealed with either a cork or screwcap.  With vastly reduced potential for taint in the bottle coupled with a much simpler opening process, screwcaps will likely win out as the preferred wine bottle closure.