The Natural Cork Story: Processing & Bottle Stoppers

The Natural Cork Story: Processing & Bottle Stoppers

Trent Johnson
Sep 22, 2010

Part II of the Natural Cork Story explores how cork is processed and turned into bottle stoppers. (See Part I: Cork is a Crop.) Interestingly, much of the rise in popularity of plastic bottle stoppers is attributed to inadequate natural cork processing which produced cork taint. The process is now far more refined and tainted cork now affects as few as 1% of bottles (a rate similar to synthetic corks).

After the harvest, cork planks are stacked out doors to cure. First in large piles, and then on pallets. The amount of time left out in the elements can range from weeks to half a year. The air and sun will encourage the cork to mature, reducing the moisture content, and toughens them up. You might notice in the photo above it says "FSC PURO." Most cork is FSC-certified. In fact, when growers decide to get certified, there's not much, if anything, they have to change.

One of the innovations taken to reduce cork taint was to move from wood pallets, which could harbor TCH (the compound responsible for cork taint), to metal pallets which were more sterile and less prone to contracting TCH.

The planks are then boiled in giant steam bathes of water to remove dirt, tannins, and to generally cleanse the cork of any foreign material for anywhere from 30 minutes to 2 hours. The heat and steam also serve to soften the cork so that they can be more easily flattened. The excess water, by the way, is often used as fertilizer since it becomes saturated with tannins.

After the planks are removed from the baths and left to cool, manual labor comes back into play. Seasoned workers employ a hoe-shaped knife to scrape off poor-quality cork and trim the cork into uniform regular shapes. The cork is sorted into 6 or 7 grades of quality depending on the plant. The best grades are used for wine bottle corks while the bottom quality grades are ground up and turned into granules for composition or agglomerated cork. Below is some premium grade A cork. Lower grades would be thinner, less uniform in thickness and have an overall lower quality appearance.

The planks are then stacked and shipped off to the next step in the cork production process.

The top quality planks are then turned into corks. Machines such as this were used for many years but now the process is done with more sophisticated machinery. After a strip of cork has been punched, it is then saved for use in other cork products. The new corks are then washed and sterilized in large vats and then punched with an identifying label to show where exactly it was made.

Nothing, absolutely nothing goes to waste! In fact, even the dust produced in cork manufacturing is scooped up and fed into incinerators as fuel for the plants. Cork has an incredibly high amount of biomass and supplies a relatively large amount of energy for its weight. Below, a tractor is taking "leftovers" into the biomass burners which power the production facility.

Here, cork dust and cork biomass is being sucked through this duct to where it will be burned and power the production plant.

You'll notice that so far, there have been relatively few inputs into the cork production process. Sure, a little energy for transportation and water for boiling, but you can't really ask for much better. With the innovations the natural cork industry has taken to reduce natural cork taint rates to that of synthetic corks, there's no reason not to use natural cork in wine bottles (well, besides price). They're recyclable, the trees are not endangered or going extinct, and they employee workers at a living wage.

Stay tuned for Part 3: Agglomerated Cork for Floors, Underlayments and Other Products.

(Images by Trent Johnson)

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