Peat is made up of decaying vegetation and grasses that have formed over centuries in boggy and wet marshland areas. It has been used as a burning fuel in communities across the world for centuries. In Scotland, in particular, peat has played a central role in the drying of barley for Scotch whisky making.

When the Industrial Revolution brought trains, which, in turn carried coal across the country, many distilleries abandoned peat as a fuel, but it remained in use in the islands – and it is on the islands that it is still most widely used today.

Most of the big phenolic, smoky-flavored whiskies derive their taste from this process, and not from the any water that may have traveled through peat bogs. Peat imparts a number of complex flavours and aromas, and these are influenced by the amount and type of peat used. Peat in Scotland is graded into three categories. The deepest layer looks like dark chocolate fudge cake when it is wet, and dries into a hard fuel that resembles coal and burns slowly. The top layer, made up of the least decayed or suppressed vegetation, crumbles in the hand when dry and burns rapidly, but produces high quantities of peat smoke. The three layers are cut from the ground in spring and dried naturally during the summer, before being collected in autumn. The amount of each layer used to dry barley will affect the taste of the resulting spirit. The type of plant that forms the source component for peat will also influence the flavour. In Scotland, the major component of peat is moss (Sphagnum).

Drying barley with peat imparts phenols which adds the distinctive smoky aroma and earthy taste to the whisky. The degree of peatiness is measured in phenols parts per millions (ppm). Classic peat Islay malts such as Laphroaig have phenol levels of around 40-50 ppm, whereas peat monsters such as Bruichladdich’s Octomore and Ardbeg’s Supernova have phenol levels of over 100 ppm. However, more phenols doesn’t always mean more peatiness in the flavour. Peat has a complex and intriguing influence on whisky which we explore in this tasting.