Master Distiller Blog No.04 — The Science of Peat
David Hsieh
What it is, where it comes from, and why it ends up in whisky — on the chemistry of carbon-rich sediment, the global geography of peat-fields, and the meaning of ‘peatiness’
By David Hsieh — Master Distiller, Tankyu Distillery | Presenter, Business Whisky Guide Podcast
Adapted from Business Whisky Guide Podcast EP4 — ‘Peat and kilning, Part I’, recorded in the Scottish Highlands, February 2023.
Peat is at once mud and coal. It is built up, layer by layer, from the remains of ancient plants. When plant matter dies in an oxygen-starved environment — typically a bog — the carbon held in the tissue cannot bind with oxygen to form carbon dioxide, and the dead matter therefore carbonises slowly in place. Given long enough deposition, and the right pressure and temperature, the resulting material becomes coal. But where the sediment contains silt and sand, drains poorly, and remains heavily waterlogged, what is formed has a lower carbon content than coal and is interleaved with mineral matter. That damp, half-mud-half-coal material is what we call peat.
Islay is the peat-bog most familiar to whisky drinkers, and is invariably the first name mentioned. Beyond Scotland, however, peat is widely distributed: England, Wales, Ireland, the Nordic countries, Russia, the United States, Canada, Indonesia — even North Korea — all hold substantial reserves. On a visit to Lagg Distillery on the Isle of Arran I noticed a map painted on one wall of the visitor centre showing the world’s peat-fields; the breadth of the distribution is striking.
The connection between peat and whisky has its roots in everyday Highland life. Across much of the region surface vegetation runs to scrub and grass; there is little timber to speak of. Cutting peat from the ground was a far more practical proposition than tramping out to find firewood. Once dried, peat became the commonest household fuel for a long stretch of the country’s history.
From which springs an interesting suggestion: the reason peatiness in whisky strikes some drinkers as so immediately familiar — even pleasing — may have less to do with the spirit and more to do with inherited memory. In a country where every household once heated and cooked over peat, the smell of burning peat would have signalled coming home, being warm, being fed. The claim is not testable in any rigorous sense, but it offers a useful angle: the smell of peat existed as a cultural aroma long before it existed as a whisky aroma.
A block of peat, on its own, has almost no smell. On many distillery tours a piece will be passed around for inspection; you will detect, at best, a faint earthiness. The ‘peatiness’ carried by certain whiskies, then, comes not from the peat itself but from the compounds — chiefly phenolic compounds — released when the peat is burned.
You sometimes hear the following: ‘We do not use peated malt, but our process water runs through peat layers and is tinged yellow, so our whisky carries a hint of peatiness.’ The logic does not hold up. First, the peat strata underground have been laid down over many tens of thousands of years; if water were truly leaching flavour compounds out of them daily, those compounds would long since have been washed clean. Second, while many Highland water sources do indeed run yellow — and that is true of our own water at the distillery — brewing tea with it does not produce ‘peat tea’.
A second explanation sometimes offered is the cask. Toasted oak does carry faint smoke or coffee notes of its own, and a long maturation can bring those forward — some drinkers will then read this as ‘peatiness’. But that is a perceptual displacement, not the phenolic chemistry of real peat. To trace genuine peat-character honestly, you have to return to the burning step.
Traditionally, peat was harvested by hand: a long rectangular cutting spade was used to take it from the bog in strips, which were then air-dried for use. Hand-cut peats emerge as long rectangular bricks. Today very few cutters have the time for hand work, and most operations use mechanical excavators; the resulting peat is irregular and lumpy. The cutting season runs from spring through autumn — winter peat is too wet, and freezes too readily, to handle.
In the wider economy of how peat is used, the proportion that ends up in whisky is small. Roughly 99 per cent of the peat that is extracted goes to horticulture and agriculture: peat is acidic and rich in humic content, which makes it useful for buffering alkaline soils and for cultivating acid-loving crops such as blueberries. Peat genuinely burned for whisky malt accounts for less than one per cent of the world’s annual extraction. Stock-on-the-ground estimates suggest no shortage of supply for the next thousand to two thousand years.
But ‘plenty in the ground’ is not the same as ‘safe to extract’. The humic content of peat is full of organic material, alive with microbes and small organisms, and the peat bog itself is an ecosystem in its own right — its biodiversity cannot be reduced to a tonnage figure. The real question around peat-cutting is the impact on the local ecological balance. Scotland has, in recent years, begun to discuss what the appropriate rules around peat extraction should look like.
About the author
David Hsieh is master distiller at Tankyu Distillery. He has previously worked as a distiller at several whisky distilleries in Scotland. He holds an MSc in Brewing and Distilling from Heriot-Watt University, and is the host and producer of the Business Whisky Guide podcast, Taiwan's #1 whisky podcast.
About the distillery
Tankyu Distillery is one of Japan's few public-private (公設民営) craft distilleries, located in Higashikawa, Hokkaido. Founded in 2020, it produces single malt whisky and craft gin using pristine spring water from the Daisetsuzan mountain range — water so pure that Higashikawa remains the only municipality in Hokkaido without a municipal water supply. Learn more at tankyudistillery.jp.
Source
・ Business Whisky Guide podcast EP4 — ‘Peat and kilning, Part I’, recorded in the Scottish Highlands, February 2023.
Other distilleries, brands and producers mentioned in this article are referenced on the basis of publicly available information and the author’s personal observation, in the spirit of information-sharing rather than commercial comparison or evaluation. The references do not represent the position of Tankyu Distillery.