I love cork!
Cork is a fantastic material. I love it. A natural bottle stopper from the bark of the cork oak. The cork comes from the bark of the tree which is harvested and then grows back again. Each tree can be harvested 12-15 times during its life which can be up to 200 years. Cork oak forests, today mostly in Portugal and Spain, are also a natural habitat for many species, some endangered like the Iberian Lynx.
Before cork stoppers, most wine was stored in barrels and when it was time to drink, a glass bottle would be filled often closed with a stopper made from wood or a piece of cloth drenched in oil. It would not provide a very tight fit but the wine was not going far and would soon be consumed, by the farmers, in a tavern or at the dinner table of a wealthy family with its own cellar.
Of course this was before the time when you would bottle the wine at the winery. Wine was sold by the barrel and poured into pitchers or bottles to be brought to the table when needed. Obviously the bottle did not have to be perfectly sealed. Sadly the wine in the barrel did not stay in great condition for very long since when it was gradually emptied the wine left in the barrel would be exposed to a lot of oxygen. So when cork started to be used as a bottle stopper in the 17th century in France, it also gave the opportunity to sell and transport wine in smaller quantities.
One of the characteristic of cork is its elasticity, and only in one direction. When you push it into a bottle it will try to expand against the glass but it will not bulge up or down which makes for an extraordinary tight fit. It is also the vehicle which allows that tiny bit of exchange with the air that helps mature a good wine over the years, a slow process but worth the outcome. We mature our Cabernet Sauvignon Reserve first in barrel for two years and then in the bottle for 5 years at least to get flavors of olive, cedar, smokiness, earth, coffee, chocolate to mix with the fruity cherry and plum flavors from the grape. I depend on getting the best corks for aging the wine this way.
While cork is a great material it also has some deficits. Mold and modern pollution can be absorbed by the bark on the tree and evolve into TCA, a chlorine compound. Wine where TCA has developed smells awful, moldy, flat and void of any fruity flavors usually referred to as "corked". As this problem became more widespread the cork producers started researching cleaning procedures for cork and today steaming and high pressure gas is used to clean the cork of TCA to a point where it cannot be detected.
Getting the cork from a supplier with a rigorous quality process is very important for a winery. I spend quite a lot of money on really good cork since I know that our red wines will be aged for many years. Just as with a number of sustainable practices, the cork stopper is not 100% perfect, but I still think it is the best closure today.