Corks, like rubber bands, freak me out because of their eyeball hitting potential. If you ever see me around a corked bottle (or a rubber band) you'll probably notice me being very...let's call it proactive...about not making eye contact with the cork. Or rather, not letting the cork make eye contact with me (ha).
I had never wondered about the corks in my beer (and sometimes wine) bottles beyond their abilities to put an eye out or to turn evidence of my beer drinking habits into quirky craft projects.
As it turns out, the unassuming yet potentially marauding cork has an interesting story.
While reading Wild Brews by Jeff Sparrow - an excellent book for anyone interested in learning a lot about beers made with wild yeast - I learned that corks come from the bark of the cork oak, also known as Quercus Suber. The cork oak can live up to 250 years and is grown mostly in the Mediterranean Basin of Western Europe and Northern Africa. It has very thick bark, which is harvested as cork.
Things a cork oak can do when it turns 25: have its bark harvested and rent a car.
After the first harvest of bark once the cork oak is 25-years-old, the bark can be harvested again every 9-12 years. The super cool thing about cork oak is that it can regrow its bark, so it is a renewable resource and harvesting it does not harm the tree. Also, it looks cool AF after it's been harvested:
The bark, which is harvested by hand, can be compressed to half its size without losing any of its flexibility. Because it attempts to return to its original size, a cork forms a seal by maintaining constant pressure within the bottle.
There are several different types of cork. Natural cork is actually made by punching the cork directly from the bark and then cutting it to the correct length. Champagne corks begin life straight-sided and become mushroom shaped after being put into a bottle. They are also not solid cork like natural cork is, but rather are disks of cork mashed together, sort of like the "wood" furniture you can buy at Target or Ikea.
Corks are traditionally used in beer bottles for the same reason they are used in champagne bottles: they can withstand a lot of pressure. Being able to withstand a lot of pressure is why corks are used for bottle conditioned beers, such a traditional Belgian beers.
A bottle conditioned beer is a beer that gets its carbonation through a refermentation in the bottle. Instead of carbonating the beer with forced carbon dioxide, a brewer can add a small amount of priming sugars to a beer. The yeast remaining in the beer will eat the priming sugars and in turn will produce carbonation. A bottle conditioned beer can have a silkier texture, more complex flavor, and a longer shelf life than a force carbonated beer. The carbonation produced in the bottle creates a large amount of pressure, which is why the cork is needed. If a standard bottle cap is used on a bottle conditioned beer, the pressure would likely force the bottle cap off, causing yet another projectile that can blind me.