As I've researched the many issues surrounding cork and its alternatives, a central theme has emerged: Little solid research has been done into both the chemistry of wine aging and the impact of bottle closures on that process. While new studies seem to be announced almost weekly now, there is a paucity of historical data and controlled long-term studies. Combine this with all of the new products being rolled out by the closure companies, and it's a dizzying issue.
Somewhat understandably, the closure industry and wine producers are quick to tout any aspect of a new study that remotely supports their closure -- or points out a potential problem with a rival. Cork producers do it, as do wineries that have opted to continue using corks. Screwcap producers do it, as do wineries that have switched to screwcaps. It's much like the constant barrage of soon-to-be-contradicted health headlines -- this month's weight-loss savior is next month's scapegoat.
So if you want to explore the topic in depth (and not be sold someone's company line) to whom do you turn? My recommendation is Jamie Goode of the website Wine Anorak. I've followed his blog for many years, and he's particularly gifted at cutting through spin and explaining the science of many wine technology issues in terms I can understand.
Goode has been very active in the closure debate, writing numerous articles and one of the few books on the topic, Wine Bottle Closures (Flavour Press, 2006). I ordered a copy and enjoyed the way it walks through the science of the issues presented by closures as well as all of the research on the performance of corks, screwcaps and artificial corks. I highly recommend it, and this post wouldn't have been possible without it.
The genesis of alternative closures is cork taint. If this fault hadn't existed, no one may have bothered to develop other ways to close a bottle of wine. However, they have, and now these alternatives have taken a substantial share of the closure market.
The other main issue relating to closures is the amount of oxygen transmission they allow. The latest research shows that some minuscule degree of transmission is beneficial. However, there are great difficulties in measuring this accurately, even under laboratory conditions. In addition, given the complexity of the reactions involved in aging a wine as well as the heterogeneity of wines, it's not yet possible to predict with any accuracy what the "right" level of oxygen transmission is for a particular wine.
So, with these issues in mind, I offer a brief introduction to the main alternative closures, along with an overview of their strengths and weaknesses.
Dave Nelson
Extruded (top) and molded (bottom) plastic corks
Several manufacturers have taken one of two approaches to building a better cork from plastic: molding or extruding. The molded plastic corks are generally quite hard, while the extruded ones have spongy innards surrounded by a firmer casing. While these closures do not transmit cork taint, they transmit oxygen at a much higher rate than natural cork. This results in significant early oxidation of the wine, essentially killing it.
However, plastic cork producers have continued to refine their products, and improved versions are being released. For now, plastic corks are best for wines meant to be drunk within a year or two of bottling.
Aggregate Corks
The cork companies have also been busy coming up with new cork-based products that address the shortcomings of natural corks. These products involve constructing cork-shaped closures from a mixture of fine cork particles and an adhesive, sometimes with a thin layer of whole cork on the end. A few of the early attempts were disasters, as the manufacturers didn't properly account for cork taint, resulting in the contamination of a lot of wine (and several lawsuits).
As with plastic corks, the process has been refined, and some manufactures now subject the cork particles to processes that are supposed to reduce the level of TCA, the chemical responsible for cork taint, below the threshold of human perception. One of the most successful of these, the DIAM from Oeneo, now comes in three varieties, each of which allows different levels of oxygen transmission. Those companies that truly are able to take TCA out of cork should have a bright future.
Screwcaps
While these closures have been around for a long time, their application to wine is recent. They have spread quickly, particularly in New Zealand and Australia, where they now close the majority of the wine bottled (more than 90% in New Zealand).
A screwcap functions differently from a cork. Instead of filling the neck of the bottle, the screwcap pushes an elastic liner inside the cap onto the edge of the top of the bottle. Traditionally, this liner contained a layer of metal foil that resulted in an extremely tight seal -- so tight that it might adversely impact the ability of the wine to age by trapping unpleasant compounds. There is not sufficient data to indicate to me whether this is a significant issue.
In addition, winemakers can choose a different liner, called the saranex liner, that allows more oxygen transmission, and may well prevent this issue from being a problem. New liners are also in development that will allow more choices in this variable. As with the other alternative closures, there is much research to be done.
The big advantage of the screwcap is no TCA taint from the closure. Otherwise, the "advantages" are really matters of preference: opening the bottle without a corkscrew, re-closing the bottle easily and storing the bottle standing up for the long term.
So where does this leave us? Without a perfect solution, due in no small part to our lack of understanding of the underlying problems. I expect this issue to continue to evolve rapidly, but vigilance must be maintained to separate the spin from the substance.
Personally, at this point I'm happy to have any of these alternative closures in a bottle I purchase, especially if it's something I plan to consume in the next year or two. For bottles that need some age, I've had no problems with screwcaps, nor would I worry about an aggregate cork, assuming the manufacturer really has figured out how to eliminate the TCA. I am, however, prepared to change my position as more data becomes available. As always, my primary concern is that the closure not damage the wine.
