Hacking Whisky: Why The Best Peated Scotches Taste The Way They Do

Peated whiskies are quintessentially Scottish. Indeed, they are part of the indelible DNA of Scotch malt whisky. They’ve also proven to be very popular with consumers. Today, you can find peated malt whisky from Ireland to Australia. Even the growing trend for American malt whiskeys prominently features peated whiskey.

Peat is an accumulation of partially decayed vegetation. It develops in areas where organic matter is covered by water before it can fully decompose. The resulting material can build up over thousands of years to form peat bogs hundreds of feet thick. The phenomenon is also known as muskegs in North America.

When dried, peat can burn. In those parts of the world where there is an absence of trees, peat has often been utilized as a source of heat. This practice can even occur on an industrial scale. There are still over a hundred-peat fired electricity generation plants, mostly in Scandinavia. During the 1960’s, 40% of Ireland’s electricity was produced in peat fired power plants.

In the western islands of Scotland, especially on Islay, and in the Northern Highlands, peat was historically burned to produce heat during the whisky making process. Most of the time the smoke produced by the burning peat had no lasting effects on the whisky.

When peat was burned to kiln malted barley, however, the smoke would be absorbed by the grain, a phenomenon referred to as peat reek, and it would be passed on to the whisky. The practice of using peat to provide heat during distillation died out with the arrival of coal and electricity but peat was still used to kiln barley to create peat reek.

Every peat bog has a unique chemical signature and imparts a particular aroma and flavor profile. Differences in vegetative composition and the prevailing climate both affect the characteristics of the peat reek produced.

In areas where there is a lot of rain, for example, the peat has a large proportion of sphagnum moss. The phenolic compounds that give peated whiskies their pronounced medicinal character are concentrated in the cell walls of the moss. The more moss, the more phenols are released by the burning peat and the more medicinal flavor in the whisky.

Phenols are a large family of chemical compounds that occur frequently in nature. If you want to get technical, they consist of one or more hydroxyl groups (—OH) bonded directly to an aromatic hydrocarbon phenyl (−C₆H₅) ring. You asked!

Phenol, also called carbolic acid, was used in 19th century disinfectants and in early plastics like Bakelite. That’s why peated whiskies can sometimes have a medicinal/disinfectant or plastic-like aroma. It’s still the active ingredient in oral analgesics such as Chloraseptic spray.

In Islay, maritime influences additionally affect the peat. When burned, that peat can add a more pronounced aroma of iodine or smoked, oily fish. Think kippers. 

In Eastern Scotland, the climate is much drier. The resulting peat has less moss in it so it lacks the overtly medicinal quality typical of Western Scotland. It tends to impart flavors of cold smoke and dry brush. Think of the aroma of a pile of burning dry leaves.

In the Orkney Islands, among other places, much of the peat derives from partially decomposed heather. When burned it adds a delicate, floral, potpourri like quality to peat smoke.

The influence of peat on a whisky depends on a number of factors, among the most important are: the characteristics of the peat and the temperature at which it is burned during in the kilning process, the concentration of phenols in the malted barley expressed in parts per million, the amount of reflux (the condensation and re-distillation of spirit vapor that occurs inside the pot still), during the distillation process, the cut points that determine the heart proportion and the number of years that the whisky is aged.

For example, peat generally burns at a temperature of around 350° C. Wood, by comparison, when fully combusting, burns at a temperature of around 600° C. Excessive combustion temperatures degrade the peat aromatics produced, although the impact varies depending on the phenol type.

The phenol guaiacol, for example, imparts flavors of kippers, smoked bacon and old cheese to a whisky, while cresol, another phenol, imparts medicinal flavors of disinfectant and antiseptic. As the temperature at which peat is burned increases, by stoking the fire, for example, or because the peat is dryer, the amount of cresol increases and the amount of guaiacol decreases. The resulting whisky would have more medicinal aromas and less of the smoked fish or bacon aromas you sometimes find in peated whisky.

Take Lagavulin, one of Islay’s iconic peated whiskies. Lagavulin’s malted barley has 35 parts per million phenols. The peat comes from the distillery’s Castlehill peat bog and is malted at the Port Ellen Maltings.

Laphroaig, its Islay neighbor, just 10 minutes down the road, comes in at around 45 ppm phenol. Most of its malt is also produced at the Port Ellen Maltings, but the peat is drawn from Laphroaig’s own Glenmachrie peat bog. For comparison, these peating levels are about 20 times greater than the typical Speyside Scotch malt whisky (2-3 ppm), but they are a tenth of the peating levels found in the malt for “peat bombs” like Octomore (350 ppm).

Compare the aroma and flavor of Laphroaig to Lagavulin. Both have a medicinal quality on the nose. Lagavulin has an oilier, fresher quality, while Laphroaig seems drier. Think of the difference between smelling an open bottle of Pine Sol and smelling a dry pail that formerly held a solution of Pine Sol and water. Laphroaig has higher cut points than Lagavulin. That’s one reason why its medicinal notes, while pronounced, seem drier, less intense, even though it starts at a higher peating level than Lagavulin.

Lately, the consumers interest in peated whiskies have led distillers to list the ppm phenol in the malt on their whisky bottle. This is a little deceptive as this is a measure of the ppm phenol in the malted barley. The intensity of peat derived aromas and flavors in the wash, however, are degraded by its passage through the whisky making process.

Depending on how the distillation is managed, its length, the amount of reflux produced, and the cut points used to obtain the heart cut, the ppm phenol in the new-make spirit can be from a third to two-thirds less than the original concentration in the malt. For most whiskies, it drops by about 40% or so during distillation.

Take the examples of Lagavulin and Caol Ila. Both distilleries, about 45 minutes apart at opposite ends of Islay, are owned by Diageo and use identically peated malt when making peated whiskies. Not all of Caol Ila’s whiskies are peated, however.

Lagavulin begins capturing the heart cut at 72% ABV and continues till it reaches 57% ABV. That’s among the lowest cut points in the industry. That also means more of the phenolic compounds make it into the final whisky.

Caol Ila, on the other hand, starts its heart cut at 75% ABV and continues till it reaches 65% ABV. There are a number of additional differences between the sister distilleries. Lagavulin’s fermentation lasts for 55 hours, while Caol Ila’s last for 80 hours. Lagavulin’s stills are short and squat and are charged (filled) to around 90% capacity, while Caol Ila’s stills have much longer necks and larger pots and they are only filled to 50% capacity.

The longer fermentation makes Caol Ila’s whisky much fruitier. The higher cut points and the greater reflux make it lighter and results in less phenolic compounds in the whisky. So even though both peated whiskies began with the same concentration (ppm) of phenols in the malted barley, the end result is substantially different.

Finally, the ppm phenol in spirit drops over time. An 8 YO Lagavulin has a higher concentration of phenols than the 16 YO, and both are higher then the 25 YO. Indeed, its reputation notwithstanding, the phenols in an ultra-aged Lagavulin, think 25 to 30 years, can be quite subtle and are much better integrated then the phenolic blast you get from a young Lagavulin.

Ready to delve further into the world of peated whiskies? Start by deciding what you’re looking for. If you want pronounced medicinal, smoked fish, disinfectant aromas look to the western islands, Islay in particular, or Western Scotland.

The usual Islay names, Lagavulin, Ardbeg, Bruichladdich’s Port Charlotte or Octomore range, Bowmore or Laphroaig will suit you, so will whiskies from the other western islands like Talisker (Skye) or Ledaig (Mull).

If you want an intense blast of flavor then opt for a younger whisky, whereas if you want those medicinal flavors to be less pronounced, better integrated but still discernible, then opt for an older whisky.

If you want the peat influence to be subtler, less medicinal and more cold smoke and earth/brush, then look at Caol Ila. Oban is similar but even more subtle. Both whiskies are from Western Scotland. Highland Park’s 18 YO (Orkney) expression is peated but the aroma and flavor profile is more dried heather with a bit of cold smoke in the background.

Peated whiskies that are finished in sweet wine casks add sweetness and dried fruit flavors over the smoke and medicinal character imparted by peat. That’s a winning combination and has proved to be very popular. Look at the Lagavulin Distiller’s Edition or the Laphroaig PX Cask. From Eastern Scotland try the Glendronach peated expression or, if you can find it, The Macallan Rare Cask Black Edition.

Historically, many Speyside whiskies had a peat component in their single malts. Typically, this would add about 3-5 ppm phenol or so. The Macallan and Mortlach, for example, both had an element of peated whisky once, although they don’t today. For a classic example of peated Speyside malts as they would have tasted 50 years ago, try Benromach or Glen Turret Peated Edition. Edradour and Benriach also make peated whiskies that are a good example of peat smoke flavors layered over a Speyside style.

For a subtler peat influence try the Glenlivet Nadurra Peated Whisky Cask Finish. Bottled at 61.5% ABV, this is reminiscent of what Glenlivet would have tasted in the early 19th century. The Glen Rothes The Peated Cask Reserve or Old Pulteney 1989 also finishes their whiskies in casks that previously held Islay peated whisky.

Finally, don’t ignore the peated offerings from the specialty bottlers. Peat Monster, from Compass Box lives up to its name and so does Big Peat from Douglas Laing.

Cheers