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Natural Cork, Screw Caps, Plastic Plugs Research At UC Davis To

I confess to being a research junkie and being intrigued with all things wine. UC Davis has a new research project to answer the question: Which is better, natural cork or aluminum screw caps? Researchers have 600 bottles of sauvignon blanc for this study into oxidation. Well, from my perspective what a waste of such a fine product from such a fine winery - PlumpJack Winery. Anything for science.

A few years ago I got into a friendly debate at a dinner party and a few of those in attendance said screw tops for wine were fine. I said, not so quickly; don't fall under the advertising spell of the aluminum industry. Thus started an expensive accumulation of data to prove or disprove my personal preferences for cork. But, with good science I was willing to change.

After some searching I found the Cork Quality Council in Sonoma, CA. This lead me along a winding path of discovery into the history, science, styles/grades of cork and proper handling of cork for wine. Just like the white oak species used for wine barrels, there are standards for cork used in wine. That's probably why the best corks come from Portugal.

The study is to analyze oxidation levels of wine using cork (natural and synthetic) versus screw cap closures. The theory is that wine will change color due to oxidation over the course of a year. The analysis on color change are measured, using scientific instruments, every 3 months-screw cap versus natural cork. At the end of the test period, the wines are categorized by degree of color change and then the chemical analysis starts followed by taste tests. John Holland, writing for The Modesto Bee, says the taste testing will be done by a sensory panel-people good at sniffing and tasting.

Remember the 1976 Paris Tasting? How did that turn out for them; those folks with finely tuned sensory receptors?

I enjoy wine the most when I am relaxed and have the patience to fully use all my senses-the aromas, the color, the texture of the wine in my mouth and the taste. Unfortunately, all of my senses are unique to just me. A possible flaw: The UC Davis cork versus screw cap research uses color (Spectrophotometer/spectrometer analysis) to measure oxidation levels.

A concern with color measurement is that it does not have a control that recognizes the slight color provided by the natural oak phenolics in cork. These are similar to the compounds found in oak barrels, and they will yield a golden color that is not associated with oxygen ingress or traditional aging variables of time and temperature. These variations are recognizable to the naked eye.

We know that oxidation occurs when the oxygen molecule reacts with other molecules, it negatively impacts cell and creates a free radical... hence the anti-oxidant craze in the supplement industry. Over time, oxygen can work against molecular structure in wine and thus will change taste, aromas and yes, color. Cut an apple open and leave it exposed to air and notice the color change and smell and taste of that apple.

PlumpJack is a highly respected producer of premium wines and they should be applauded for taking the lead on this research. In that they use both cork and screw cap closures they have much to prove, either way. Cork Quality Council has also done a great deal of research on all things cork and they are always anxious to share their cork research with anyone who has questions. So, I am puzzled by the statement from wine chemist Mr. Andrew Waterhouse when he said, "we won't be declaring that one type of closure is superior to another. Rather, we'll be giving winemakers information about the variability of each type (closure) so that they can determine which is most appropriate for use in bottling their wines." So, after 350 years of using cork in wine bottles there are questions as to its appropriateness in wine?

In that white wine is not generally collected and aged, it will be interesting to see the impact of plastic seals in screw caps versus cork. If white wine is consumed shortly after purchase, oxidation frankly may not be that big of an issue. As an aside, "synthetic cork" is an oxymoron; cork is cork, synthetic cork is a plastic plug for closure.

Yes, I like natural cork, especially high quality cork. I learned a lot about cork and TCA tainting from Peter Weber-probably more than I ever wanted to know. The only negative comments about cork involve the chemical compound called TCA. This is the compound that gives a musty smell or 'off' taste to wine and is airborne. Once TCA gets into a wine making process it can contaminate wine. It can be introduced through a number of sources such as equipment, barrels, etc. But, it is the cork that has taken the rap for TCA issues. To put this issue into perspective, TCA's are measured as single digit parts per trillion units. o address TCA's and all cleanliness issues the handling of cork in a winery is a hermetical approach. In fact the process from manufacture to the winery is highly controlled to ensure a clean cork. I really enjoy the fresh and clean smell of new cork. Try that experience with aluminum screw caps. I hope my true feelings aren't showing?

Probably best summarized by Tettie Teague writing in "Food and Wine", "The fact is, as Larry Stone, wine director at San Francisco's Rubicon restaurant (and a supporter of screw caps), points out, TCA can come about without a cork. And of course, screw caps have their own set of problems, such as leakage: A screw cap leaks more readily than a cork. A metal cap can get banged up (sometimes, as I've discovered, so badly that it can't even be unscrewed). In addition, a screw cap can be sabotaged, as the owners of PlumpJack discovered when someone-presumably bent on salvation-stabbed a knife through one. Finally, and most important, it's too soon to know whether a screw cap wine will age well. We know what a Lafite or DRC tastes like aged for 10 or 20 years in a bottle closed with a cork. But nobody really knows what a few decades under a piece of metal will do." Enough said and now I move on.

Next point to consider, as these researchers are comparing cork to screw cap performance, is the quality of the cork. There are at least 8 grades of cork.

There are 4 grades of natural whole cork. Cork grades are based upon fiber structure, size, and number of crevices. Within these 4 grades there are options for diameters and lengths. The better the quality the longer lasting the cork (especially when the bottle is properly stored). Price for the top performing cork, with printed logo is approximately $1.15 and of course depends on quantities.

Then there are less expensive options using aggregated and/or agglomerated corks. These are made of pieces of cork that are bonded together and work perfectly well for a few years but then can deteriorate. These corks can cost from $0.20 to $0.05 each.

The point here, relative to preventing oxidation, is that the best grades and sizes of cork perform perfectly.

The process of getting corks to the bottling line takes approximately 3 years; that is from harvesting the bark of the tree (a species of oak), through cutting out the cork, drying the corks and sealing the bags of cork to ensure cleanliness. When put in the bottle the corks are compressed by approximately 20%. This compression, and the cork being exposed to the wine, makes for an air tight seal.

Let's move away from discussing oxidation to focus on the other functions that cork performs on the ultimate sensory experiences of wine-the aroma and taste. Remember this is a secondary part of the UC Davis study commissioned by PlumpJack.

Cork was researched and analyzed relative to the beneficial properties in the mid 1600's. That was when it was discovered that the seal available from cork for wine solved a multitude of problems when used to replace the old oil soaked cloth stoppers.

In a 2005 study that was conducted concerning gas permeability of cork. It was found that 45% of corks had this happen. This was good, in fact it was great! A good screw cap will eliminate any oxygen reaching the wine. This is not good, according to some wine experts, especially for red wines, because wines need some oxidation to form aromas and character. Further, the fact that cork is from the oak species tree many feel that the process of oxidation and the cork's contact with the wine adds flavors. Remember, the process of aging wine in oak barrels also allows oxygen to come in contact with the wine. Approximately 5% of wine is lost through the porous wood barrel.

To end on a note that imbues a warm feeling about a well made wine... OK let's say it is a PlumpJack sauvignon blanc, let's talk about the environmental impact of cork versus screw caps. In Sally Eaton commented about the study "Analysis of the life cycle of Cork, Aluminum and Plastic Wine Closures," commissioned by cork manufacturer Amorim and made public in December 2008, concluded that cork is the most environmentally responsible stopper, in a one-year life cycle analysis comparison with the plastic stoppers and aluminum screw caps. Cork harvesting is not destructive to the cork oak tree, no mechanization is used in harvest, and it's a totally eco friendly process.

UC Davis is focused on PlumpJack's fine sauvignon blanc only. Final findings are somewhat subjective. Not subjective is the fact that natural cork is a sustainable closure-worldwide. My corks go into my trivets and in my "memory of wine's I like" box. But, I would say, what's good for whites-- is good for whites. I am biased, but not for any personal gain; I just like the feel, look, and sound of cork coming from a bottle of wine. And, I enjoy the feel of a nice natural cork pressed between my thumb and forefinger.