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What About Plastic Corks and Screw caps?

by David on September 3, 2009

This is a subject that has raised a lot of questions because things have changed rather rapidly. Lately, when you buy wine you’ve probably noticed that, more and more often, the standard natural cork has been replaced by other closures like plastic corks or screw-caps.

Why is this happening? The two main reasons are cost and frustration due to imperfections in the cork. Here’s a little background:

The first duty of any closure is to seal the bottle and protect the wine from oxygen. In that regard, cork has proven to be an excellent closure over a number of centuries. It swells when it comes into contact with moisture and creates a tight seal. The downside is that cork is the bark of the cork oak tree, and we can’t exercise absolute quality control over tree bark! Click here for “Corks: from the tree to the bottle”. If the cork fails to perform properly and doesn’t swell into the neck of the bottle, the wine is exposed to too much air and it spoils. Fortunately, spoiled wine isn’t harmful, but it can be offensive. When the wine becomes oxidized, initially it may lose its freshness and fruitiness. As the spoilage progresses the wine browns and develops off aromas such as fingernail polish or vinegar.

The most common problem associated with cork is that sometimes microscopic fungi, in the presence of moisture, convert naturally occurring chlorophenols into chloroanisole. The compound that gets into the wine is called 2,4,6 trichloroanisole, or as most prefer to call it, TCA. It can make the wine smell “corky” like an old, dank basement or moldy newspapers. Other chloroanisole contaminants have been identified, too, that similarly detract from the wine. The good news is, again, that it can’t hurt you. The bad news is that it stinks!

CorkCorks aren’t the only source of TCA in wine. It can come from contaminated barrels, air-born molds or molds in containers, especially wooden boxes. TCA can also be found in fresh produce that has traveled in wooden boxes and in other food products due to contamination during processing. For wine, the cork is still the most likely culprit.

While the human threshold for detecting TCA is measured in parts per trillion, some of us are more sensitive than others. In very low concentrations, TCA may simply deaden the fruity aromas in the wine without it being obviously due to cork taint. As the level increases, it becomes more identifiable and offensive.

The exact incidence of cork taint is hotly debated. Estimates range from one to 8 percent. This is true regardless of the region of origin or quality of the wine. Quality control can reduce, but not eliminate the incidence of cork taint. However, there’s some very encouraging work being done in this area. For more on this click here for “Corks, from the tree to the bottle.”

Plastic Corks

Between the cork taint issue and the relatively high cost of corks, many wineries have gone to other closures. Unless you only drink luxury wine, you’ve probably pulled a synthetic cork out of a bottle. These are made from a co-polymer material (plastics from the polyethylene group). Of course, the most important advantage is that there is no TCA.

Plastic corks seem to be fine for wines that are intended for early drinking but, so far, they allow too much oxygen exposure for long term aging. Again, the duty of any seal is to protect the wine from oxygen, and the polymers don’t provide as tight a fit as a good, natural cork. Experts believe this problem will be solved in the very near future. But with the synthetics, for now, we’d recommend you emulate the average American wine consumer which means the bottle  aging  amounts to the approximate time it takes you to drive home from the wine shop!

Screw Caps

You’ve probably noticed more and more wines finished with a screw-cap, especially those from the southern hemisphere. The thing we all used to joke about is becoming mainstream! Statistically, they are superior to natural cork in preventing oxidation. The only problem is that we don’t have enough data to predict how the screw cap will perform beyond a few years, so we can only recommend it for the short term for now. There’s also evidence that, as a result of such superior oxygen protection, the wine may actually become “reduced”, over time, due to lack of air. Reduced wine usually smells like burnt rubber. The incidence of this is extremely low, and given that most of us don’t bottle age our wine, the risk is minimal.

In response to these concerns about reduction, screwcaps come with two different liners for wine: For something similar to the permeability of a cork, the screwcap is lined with saran (plastic) only. For the least exposure to oxygen the lining includes a layer of tin. It is easy to tell them apart: The saran liner is white and the tin/saran liner is silver.

Still, for many people, there’s a certain lack of romance in twisting off the top rather than pulling out the cork. Screw caps have been very well received in Australia and New Zealand, but in America and Europe, we’re a little slower in accepting them (so far).

Crown Caps

Crown caps or crown seals, which are just like Coke bottle tops, work as well as screw-caps, but are not reseal-able. Sparkling wine producers have used crown caps for years, while aging the wine on the yeast, before finishing the bottle with the cork. Very recently a few sparkling wine producers including Domaine Chandon, a prominent producer here in California and part of the Moet et Chandon group, have begun packaging their finished wines with the crown cap!

The Maestro Sparkling Wine Closure

This new closure takes the danger (and perhaps the excitement) out of opening a bottle of Champagne or sparkling wine. It’s essentially a crown cap covered by plastic and foil. It features a lever, which removes the risk of losing your eye to a flying corkbut still makes the delightful popping sound. Of course, there is no risk of cork taint and, statistically, it’s at least as effective as the traditional Champagne cork as a seal according to Alcan, the producer. It will be interesting to see if these catch on.

The Zork

Have you come across a Zork yet? It’s quite ingenious and is meant to combine the attributes of the screw cap and the plastic cork. It consists of a plastic pull strip that looks somewhat like a wax seal on the outside of the bottle and a plastic plunger like a “stopper cork” for Port. It is very easily removed. It makes a nice pop when you pull it out of the bottle and can be re-inserted if you don’t finish your wine (what a thought!). The special feature, besides the fact that you don’t need a corkscrew, is that there’s a metal foil on top of the plunger that keeps the air out in the same way a screw cap does. Again, this should be fine for the short term and we’ll have to wait and see about the long term.


A small number of wineries have adopted an upscale cork alternative called the Vino-Seal or Vino-Lok. It looks like a small glass stopper and it has an inert, rubber-like, o-ring to create an air-tight seal. Again, we don’t have enough data to know how the Vino-Seal will perform over the long haul and so far it’s the only cork alternative that costs more than a natural cork instead of less.

Interestingly, all of these alternatives are available to us now that cork growers and brokers are extremely close to solving the cork-taint issue. The industry was quite complacent until about 10 years ago, when the first alternatives made an appearance. Since then, they’ve swung into high gear to solve the cork taint problem, and with remarkable success. Very recently, enologists have come up with ways of measuring minute quantities of TCA in large samples of corks, replacing the far less accurate sensory evaluation tests we’ve done in the past. Our supplier uses these tests so that they can refuse corks before they leave Portugal and they run them again when the corks arrive in California. In addition, they’ve developed a machine that purges the TCA from corks, so it appears that cork taint may not be an issue in the near future.

With all of this excellent progress in the closure end of things, it leaves the field and future wide open. We, here at Goosecross, prefer natural cork as our closure for a variety of reasons, environmental ones in particular (the plastics aren’t biodegradable). But with all of these choices, what will you want and expect from us as producers? Will the priority be a bottle that can be opened easily, without a cork screw, or will we all revert to the romance of cork? Or some other alternative?

Stay tuned…

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