Peat and Whisky

What influences the peaty/smoky/medicinal character of some whiskies?

As I’m sure readers will know, peat is compressed and partially decomposed plant matter in waterlogged areas known as peatlands, peat mosses or peat bogs. The principal plant components are sphagnum moss, grasses, sedges, heather and bog myrtle. Since these vary in proportion and variety from moss to moss, so the character of the peat and the fragrance of its smoke when dried and burnt will vary; the peats cut - the correct term is ‘won’ - on Islay are different from those from Aberdeenshire or Orkney. Peat’s principal ingredient is sphagnum moss, known for its antiseptic properties (it was gathered by volunteers during World War I to dress wounds), and it may be that it contributes to the medicinal flavours of some whiskies.

The chemicals which contribute smoky/medicinal flavours to whisky are generically called ‘phenols’, a family which includes phenols themselves, guaiacol, cresol and others, measured in parts per million (ppm). Each compound contributes its own range of flavours - from creosote, coal tar and carbolic soap, via TCP, iodine and antiseptic cream, to smouldering embers, smoky bacon and lapsang souchong tea. Peat is the most chemically complex raw material used in the whisky-making process.

Peat smoke, laden with phenols, only adheres to the ‘green malt’ in the drying kiln when the malt is damp. So during the early hours of kilning what the operator wants is not heat but smoke; a hose is invariably on hand to extinguish any flames in the smouldering peat fire. Once phenol levels have been achieved they are measured and usually the peated malt is then blended with non-peated malt to the individual distillery’s specification.

The intensity of such flavours depends not only on how heavily peated the malt is, but also on how early the still operator comes off spirit. Phenols are large molecules with a high boiling point, so only vaporise towards the end of distillation, making it possible to reduce the ppm in the spirit by cutting early. Phenol levels also decrease steadily during maturation, so as a general rule if you’re a smoke-head buy young. I should mention that ppm levels in spirit are about half of what they are in peated malt, although many wicked marketers confuse the two measures to make their products sound more phenolic!

---------------------------------------

In October last year I was asked to review a book for The Keeper magazine - Peat and

Whisky: The Unbreakable Bond by Mike Billett (Saraband, 2023). I concluded my review: “I believe this to be among the most important books about whisky ever written”.

I have never met Dr. Billet and am not given to hyperbole - indeed my reviews tend to be curmudgeonly – but his scholarly investigation of the subject was thorough, engaging and charmingly written.

Peat is of key importance to the Scotch whisky industry, both historically and today – esteemed ‘Highland’ malt was distinguished from Lowland malts, let alone grain whiskies, by being dried over peat fired kilns. But, more important, peatlands play a crucial role to our planet in absorbing carbon dioxide and mitigating global warming.

“They are nature’s own carbon capture and storage system, but only a healthy, functioning bog will be effective at drawing down carbon dioxide from the atmosphere”, writes Mike Billet. “In places like the Flow Country, an estimated 400 million tonnes of atmospheric carbon has been captured in this way since the end of the last Ice Age, storing more carbon than all of the nation’s forests”.

Peat mosses are ancient. They began to form after the last Ice Age, around 12,000 years ago – some of the deeper peats won today will have been plants when mammoths wandered the earth. Peat accumulated at a rate of between .5 and 1.00 mm a year, so it can take 1,000 years to create a metre of peat. Peatlands retain a record of past climatic fluctuations, as successional changes in vegetation over thousands of years by preserving tiny grains of pollen: under a microscope peat becomes “a window to the past”.

For Mike Billett peat smoke – both in itself and communicated by whisky - is “comforting, soulful, timeless, even romantic… a unique sensory feeling”. It is also atavistic, raising distant ancestral memories of warmth and safety. In his Distilleries of the United Kingdom (1887), Alfred Barnard memorably described peat smoke as “the incense of slumbering ages”.

But “every peat bog has its limits and they need to be managed well over the long term to maximise their capacity to store water…. Drainage of a peatland has been likened to a knife wound – the bog will only survive and begin to heal if the wound is plugged and the life blood of the bog retained... The whisky industry needs to take care of its peat bogs, in the same way it cares for its water supply”.

Peat and Whisky is not only a joy to read, it makes a significant contribution to understanding our precious environment.