Natural Cork Stoppers from Bark

Cork is the outer bark of the cork oak, stripped from the living tree every nine years. Cork makers stack the planks outdoors for at least six months, boil them for an hour to clean them and make them flat and springy, let them settle, then cut strips and punch stoppers out with a tube parallel to the bark's surface, so the pores, which run through the bark's thickness, cross the cork instead of running along it. A stopper is cut wider than the bottle's bore and squeezed into it: that pressure is the seal.