Cork is the bark of the cork oak (Quercus suber L.) which protects the tree from heat (including fire), micro - organisms, feeding animals and dehydration. If the cork oak is 25-30 years old, the bark is for the first time manually removed from the trunk, not the branches. The oak is experiencing no damage and the bark grows back completely. The first harvest is called virgin cork. He is of poor quality, only 30-35 mm thick and has irregular structure.
KurkThe peeling is done every nine years. Of a cork oak with an age of 150-200 years can thus be harvested approximately 17 times. This happens in the hot summer months, July and August. By fluid loss the cork bark is easier to separate then from the Cambium, the thin layer between the bark and tree. The harvest wound is healed after 3 months.

The second harvest yields "secondary cork". Only the third harvest, “amadia cork", is of good quality.

The structure of cork is similar to a honeycomb and is made up of millions of closed cells. Therein and in between is a volatile substance that resembles air. This unique structure and composition ensures good thermal insulation, sound absorption and resilience.

Portugal produces 70% of the 300,000 tonnes of cork produced annually.
The specific gravity of cork is 0.12 to 0.20 kg / l. So it floates fine.
Contrary to popular belief wine does not breathe in a closed bottle trough the cork (which consists of closed cells).

The harvested bark is still half a year in the plantation to dry. For the processing, the cork is heated with steam in order to make the material smoothly through the inclusion of water.

30% of all harvested cork is used for the production of bottle closures, the rest is, after granulation (grinding) used for the production of shoe soles, cork flooring, bulletin boards or insulation.

In the 17th century, French vintners were still using in oil soaked rags instead of cork stop.
A layer of oil poured on the wine (or other content) was also sometimes used to seal of oxygen to prevent oxidation. In order to efficiently use these sealants are bottlenecks also much narrower than the bottle itself.

Cork is resistant to heat (good insulator) and pretty fire resistant. It can be burned at very high temperatures, but does not itself keep a fire burning. In practice, this will also depend on the glue with which cork granules for stopping and tiles are pressed. Of cork in the stove just ash remains. But cork so, contrary to what is sometimes claimed, will burn (without toxic smoke unless glue or varnish). It has a flash point of 300 to 320 degrees.

If you cut used corks into slices of about 1 cm and string them by thread, you get an excellent heat resistant trivet.