by Richard Olsen-Harbich
There’s been a great deal written about the use of natural corks vs. screw caps in the wine blogosphere – mostly by folks who only have the experience of pulling them out or twisting them off. Some consumers remain hesitant to accept screw caps while others wonder if the world’s supply of cork is running out and if cork trees are killed when they harvest the bark. Not to worry - that’s why I’m here - to try and clean up some of the confusion in the greater wine world. Here’s a quick primer on screw caps and corks.
The use of cork to seal containers started around the second century A.D. The Romans used it for sealing amphora, making shoes, fishing floats and even insulation for their beehives. It wasn’t until the 16th century when it became common for corks to be used as a closure for glass bottles. By the mid-17th century, most of the European wine industry was using natural cork.
Cork is produced from a species of oak called Quercus suber, which is native to the southern Mediterranean region of Europe and northwest Africa. The tree forms a thick, rugged bark that can be harvested every 9 to 12 years to produce cork. The harvesting of cork does not harm the tree and no trees are cut down during the harvesting process. This makes natural cork a renewable resource that provides a sustainable agricultural economy for many Mediterranean countries that cover almost 2.3 million hectares of forested land. Portugal has been the leader in the sustainable development of the industry, implementing important reforestation projects; the current rate of reforestation is estimated at 10,000 hectares per year. This keeps many thousands of families employed in agriculture and provides an important ecological benefit to the region as well as to the rest of the world. Most would agree that the more land we can keep under trees the better off all of us will be. In my opinion this makes natural cork the most sustainable closure I can use - something which is very important to me.
Screw caps were developed by the French company La Bouchage Mecanique in 1964 at the request of Peter Wall, Production Director of the Australian Yalumba winery. They became commercialized in the 1970s but have come back into fashion as the hip closure of choice, especially for younger consumers. The use of screw caps in the wine industry is a direct result of the increased incidence of wines contaminated by 2, 4, 6-Trichloroanisole (otherwise known as TCA) which can be found on some corks. TCA is usually produced when naturally occurring airborne fungi and/or bacteria are presented with chlorinated phenolic compounds, which they then convert into chlorinated anisole derivatives. Older methods of cork manufacture often utilized chlorine as part of the washing process – something which is no longer used.
TCA taint can range from the smell of musty cardboard and dank basement to a subtle decrease in the wine’s aroma and flavor. It’s what happens when the wine is called “corked” - the biggest reason why wines are returned in restaurants. A lot of wine has been spoiled by TCA contamination over the years and the development and use of the screw cap was promoted as a way to decrease this problem. Some are now saying that screw caps go so far as to guarantee a higher level of quality wine in the bottle. I say, not so fast.
With today’s new and improved cork treatment protocols, screw caps do not guarantee a higher level of quality any more or less than corks do. The producer, vineyard, and climate as well as the passion and dedication of ownership, vineyard management and the winemaking team are what makes for quality wine. A wine that is insipid, uninteresting or flawed will remain that way regardless of the closure. What screw caps will do is reduce the chance that a bottle will be spoiled by TCA. However it’s also been documented that TCA can also contaminate wines in the cellar prior to bottling. As screw caps become more widely used we are seeing some of the other potential problems associated with them - the instance of sulfide production in the bottle and the more recent studies showing that some of the plastics used in the liners of the caps may absorb aroma and/or flavors over a long period of time. As with most things in life, nothing is perfect.
The number one difference between screw caps and corks is abbreviated as "OTR," or Oxygen Transmission Rate. Natural cork allows a small amount of controlled oxidation – a microscopic exchange of oxygen that enters the bottle and helps the wine age gracefully. This is particularly necessary in age worthy red wines which need this low level of oxidation in order to soften tannins and become more complex with age. Screw caps, as they get more advanced, are starting to be manufactured with special plastic liners that mimic the OTR of cork. So far, long term studies have shown mixed results and improvements in the OTR of screw caps remains a major focus of future research.
During the past ten years, we’ve seen a huge increase in cork quality and a dramatic decrease in the incidence of “corked” wines. No doubt the market pressure from screwcaps and synthetic closures have forced the cork producers to raise their game and improve their product. Cork companies are now more adept than ever at removing potential problems from production using techniques such as steam and UV light treatments to reduce and sometimes eliminate the potential for TCA contamination. The bottom line is we are now using a higher quality cork than ever before and I expect the science around this issue to get even better as time goes on.
Yes, I am a natural cork devotee - but my main point is that there is no perfect closure. Wine continues to age and develop at some level no matter how we package it. Whether you prefer the sound of a cork “popping” or a cap “cracking,” the finest wines will be made from the best and most dedicated producers. The truth is in the bottle.