Peat
An accumulation of partially decayed plant material, in areas generally known as peat bogs. Peat bogs are a very efficient carboy sink which have reached and equilibrium and grow very slowly. It can take thousands of years for a peat bog to form.
Peat is harvested, dried, and used as a fuel source in some distilleries in Scotland. Some distilleries, especially those in Islay, allow the smoke to infuse the malt during drying, which imparts a unique peat flavor to the finished whisky.