Harvesting cork requires skill, experience, and the right tools. Notice the ax-like tool in this harvester's hand, which allows him to "scrape" the outer layer of bark from cork oak trees.
Once the bark of the cork tree has been loosened, harvesters peel the layer from the trunk and branches. They drop the bark to the ground, where it is collected onto trucks and delivered to a manufacturing facility.
Harvesting the cork doesn't kill the tree. Properly managed cork forests enable the harvesting of individual trees once every nine years. Trees are left to recover and re-grow the bark in the intervening years.
Trees are carefully marked in order to track the correct year it's been harvested, which also indicates how many more years before its next harvest.
The bark is brought to a nearby manufacturing facility, where it is boiled and "seasoned" while it dries in the sun, much the way oak staves are dried and seasoned before they're made into wine barrels.
Trimmed slices of bark are then processed into the corks we recognize, as corks are "punched" out, one by one.
An ongoing and very real concern about corks within the wine industry is cork taint, or TCA (2,4,6 -- Trichloroanisole). It's a naturally present chemical compound, that is also associated with mold that's liable to be found in cork. The goal in combating TCA is to stabilize the cork wood; the Cork Supply Group (which I visited) achieves this by carefully controlling the manufacturing process at every stage, including changing the water when the cork is boiled to covering the wood while it's seasoned in the sun.
A significant and labor-intensive stage of the taint-detection process at the Cork Supply Group is the three-person team who smell-tests literally every cork, in "packages" of four inside neutral glass containers. Although TCA isn't detectable by every segment of the population, the testers at Cork Supply receive special training and responsibilities. These smell-tests, in addition to the controls implemented in the manufacturing process and ongoing investments in machinery and equipment for taint detection, have all significantly reduced incidences.