peat

An accumulation of partially decayed plant matter found in peat bogs, formed when various environmental conditions prevent it from decaying completely. It is very carbon-dense, and is commonly used as a fuel source as a result. In the production of Scotch whisky, particularly on the island of Islay, peat fires are used to dry malted barley prior to fermentation. This imparts a distinctively smoky flavor to the whisky, leading to many Islay whiskies being referred to as “peaty.” This “peatiness” is measured in parts-per-million of phenol, with most peated whiskies falling between 30 and 50 ppm, though some experimental whiskies have exceeded 200 ppm.

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