What is peated whisky?

Smoke gets into the whisky because the germinating barley malt is dried over a fire in which peat is also burned. The smoke deposits phenols on the grain kernels.

Peat is compressed plant material from boggy soil, built up over thousands of years. When it smoulders, peat gives off a smoke that differs in composition from wood smoke. The longer the maltings keeps peat on the fire, the more phenol the malt absorbs. That drying in the kiln lasts up to about 24 hours.

The phenols are therefore already in the raw material before even a drop has been distilled.

Ppm stands for parts per million and indicates how much phenol is in the malt. A higher value means more smoke compounds in the raw material.

The trade press roughly uses this scale: around 10 ppm is lightly peated, around 25 ppm medium, and 40 to 50 ppm or more heavily peated. It is a sum of substances. Phenol itself is about half, cresol about 40 percent and guaiacol about 10 percent.

A bottle with a high ppm figure on the label therefore does not automatically contain more smoke than a bottle with a lower figure.

The figure is measured on the malted barley on arrival at the distillery, not on the liquid in the bottle. Most of it is lost along the way.

During mashing, part of it stays behind in the draff. During distillation, phenols are released only late in the run, because they are large molecules with a high boiling point. Where the stillman makes the cut therefore determines how much goes along. After that, part evaporates again during maturation.

In total, 60 to 80 percent of the phenol content disappears between malt and distillate. Two distilleries that buy the same malt can therefore make very different whisky.

Islay is one of the five recognised Scotch whisky regions and has a lot of peat soil, little forest and for centuries used peat as fuel. Smoking was the logical way of drying there.

The other four regions are Campbeltown, Highland, Lowland and Speyside. A region name only says where it was distilled, not how the whisky was made. On Islay there are also distilleries that hardly peat or do not peat at all, and outside Islay peated malt is widely used, both on the Scottish mainland and beyond.

Peat therefore remains a choice of the maker, not a property of an island.

No, a ppm statement is not legally required anywhere and not every bottler puts it on. Whoever does state it chooses for themselves which figure to quote.

Some labels give the ppm of the malt, others have the amount of phenol in the bottle measured. Those two numbers are far apart, because the greater part is lost between malt and bottle. Without explanation you do not know which of the two you are reading.

So ask about the malt, the maturation and the cask rather than about that one figure. An old peated whisky and a young one with the same ppm are not comparable, if only because more has evaporated.