Natural Cork Closures for Wine

Natural cork wine have been used to seal and protect wine for the past three hundred years or so. Prior to that more crude methods were employed.

Today we are seeing a thriving synthetic closure market crop up and the debate between whether to use natural or synthetic closures is thriving. This article is the first in a series that will cover each of the different closure types available and what their benefits and drawbacks are.

Where Does Cork Come From?

Cork closures are made from the bark of the Cork Oak tree. This particular tree is native to Southwest Europe and Northwest Africa. As you can see from the cross-section of a cork oak tree the bark grows very thick.

Once it has reached an optimum thickness the bark is harvested by stripping it from the tree in large sheets. These sheets are processed and solid corks are drilled from it. The remaining cork is then shredded into small particles and used to create more cork closures or it will go into other cork products such as corkboards for displaying all those reminders we never look at.

Unlike other trees the cork oak does not suffer from the removal of its bark. It simply regrows and can be harvested again and again as it reaches the proper thickness. On average it takes between nine and twelve years for the tree to regenerate its bark.

The bark is usually harvested from cork oaks that are at least 25 years old. These trees can live to be between 150 to 250 years old even when the bark is harvested on a regular basis. So each tree goes through about twelve harvests in its lifetime.

The Benefits of Natural Cork Closures

Natural cork closures have been used for so long because there are many benefits to doing so. Previous methods for sealing wine bottles included soaking rags in oil and stuffing them into the neck of the bottle, while other cultures would pour a layer of olive oil over the free surface of the wine. The floating oil would prevent oxidation and microbial spoilage so long as the wine was not infected prior to pouring the oil.

One of the main benefits of cork closures is that they are a product of nature. Many synthetic closures are made from petroleum-based plastics that, some critics claim, leave petrol flavors behind. By in large natural corks do not impart any noticeable flavor on the wine.

Due to the long history of using cork closures we have a much better understanding of how they hold up over time and how well the wine they protect develops. No one knows how well a synthetic closure and the wine it protects will fair after fifty years in the cellar because they just haven’t been around that long.

The Drawbacks of Natural Cork Closures

There are a few downsides to using cork closures. Because they are derived from a tree they, like any other plant-based material, can dry out over time. So care must be taken when purchasing, inserting, and storing wine enclosed with cork to ensure that the integrity of the cork is maintained.

The quality of the cork matters. Lower quality, particle based corks shouldn’t be expected to last as long as premium cork or synthetic closures.

Lastly, and perhaps most importantly, as a cork is a plant product it is susceptible to spoilage organisms. They can take up residence in a cork and spoil wine in a bottle. This is referred to as “cork taint”.

The good news though is that most corks today have been treated and handled in such a way that cork taint is not a very big concern. Even wineries that produce thousands of cases per year may or may not see even one bottle affected by cork taint. Others in the industry have a different opinion on how often this occurs and thus the arguments ensue.

Different Styles of Cork

The solid cork

As the name implied this cork closure is made from a single piece of cork. The highest quality closures are made this way. This particular cork is tapered to offer the best possible seal.

Agglomerated Corks

These closures are made from small particles of cork that are glued together. While still considered a natural cork closure you’ve got to consider that the glue may have some impact, long-term or otherwise, on wine quality.

There are two varieties of the particle corks. One is made from tiny particles and the other is made from particles about half the size of a pea.

Premium Agglomerated Corks

These are a hybrid of agglomerated corks and solid corks. They have a core that is made from particles but at each end they have a 1/4 inch thick solid cork disk. The wine as well as the consumer only sees a solid cork surface.

I have used both particle based corks and the premium particle corks with the solid disks. Personally I have not done any sort of test to see which actually works better or lasts longer, however, my preference is for the premium particle corks. I’m willing to gamble the extra few cents that the solid ends will treat my wines better than the glued together particle corks. Click here for more information on #9 Premium Corks.

Tips for Purchasing & Using Natural Cork

1. Purchase corks from a supplier that has a high turn over. This ensures you’re getting fresh corks and not old dried out corks (been there).
2. Don’t soak or boil your corks. It can damage the cork and leave your wine vulnerable to oxidation or microbial spoilage.
3. Never let your cork come into contact with anything that may contain or have been exposed to chlorine. The chlorine can react with the cork and make it a breeding ground for spoilage organisms that lead to cork taint.
4. After inserting corks keep them standing upright for a period of three days. This allows the cork time to expand sufficiently to seal the wine. Then, after three days lay the bottle on its side. This keeps the cork moist so it doesn’t dry out and shrink to the point that you lose your seal.
5. Buy higher quality corks for wine you plan on keeping around for a while. Even the pros replace corks on high-end wines every ten years or so. That’s using the highest quality corks. Solid corks give you the best performance and can be left in place for many years. Particle based corks (without the solid discs) should only be trusted for a period of two years or less.
6. Hold off on those fancy foil caps until you’re ready to share your wine. You want to be able to inspect the closures to ensure there is no mold and that none of them are leaking. Foil caps and wax toppings hide all of this from view.

Micro Oxygenation

While many experts claim that natural cork closures offer a small amount of oxygen transfer through the closure this has come under debate lately as well. Some experts claim there is no evidence to support this. Either way wines enclosed with natural cork seem to age more gracefully.

Photograph of cork oak tree cross-section:  Plantsurfer

Drawing of cork harvest: unknown

Stunning photographs of the individual corks by the author.