It’s one of the most intense, evocative and recognisable smells of all. That waft of smoke on the clean night air, walking through a row of shadowy countryside cottages, perhaps in the direction of a pub. And not just any smoke, but the earthy, turfy, rooty aroma of burning peat.

It’s a smell that has been caught on the wind perhaps for millennia, given peat — slow burning, plentiful — was a near-ubiquitous fuel source for rural communities in Ireland as in many of the world’s northernmost countries. Small wonder then that, for centuries, that same fuel was used to kiln-dry the malting barley used in the making of Irish whisky.

The flavours of peated vs unpeated whisky are often discussed in rather binary terms. Smoky. Not smoky. Although this isn’t entirely inaccurate, rather a lot of nuance is lost. There is far more to the flavour of peated whisky than simply ‘peaty’.

At this point it’s worth taking a moment to examine the formation and character of peat itself. Peat burns because it is made up of organic plant matter whose decay has been slowed by the anaerobic conditions brought on by a lot of moisture and a cool temperature.

As far as the peat of Ireland (and yes, Scotland) is concerned, the bogs have been formed in two ways, both prompted by the retreating of glaciers some 10–12,000 years ago. The first style, blanket bogs, feature along the western seaboards and on higher hill and mountain masses. The onset of their formation conforms very closely to climate deterioration in the post-glacial period, as testified by the remains of tree matter such as pine stumps in areas they can no longer grow.

This deterioration of climate, combined with poorly-drained clay deposits left by the glaciers, created conditions perfect for bogs to slowly form at a rate of a foot or so every thousand years. Blanket bogs therefore are made of complex plant matter; fibrous and rooty near the top, dark, smooth and with varying degrees of timber remains near the bottom – the area from which the peat cut for whisky is taken.

The second style of bog, found further inland, is the raised bog. These are older and far deeper, achieving depths of around 9–12 metres compared to between just 1–6 in the coastal blankets.

They began their life as post-glacial lakes, rich in the calcium and magnesium of glacial till. In these lakes, vast quantities of aquatic and semi-aquatic plants began to build up, accumulate and senesce (decay) into the water. As the quantities of decaying vegetation increased, they filled the lakes and began to rise above the surface of the water, their decay continued by the ombrotrophic conditions of significant rainfall.

As a result, these raised bogs boast an extremely high concentration of sphagnum moss in their makeup, with a much more pronounced difference in age, texture and humification between the layers of peat the deeper into the bog one cuts.

It doesn’t take a great mental leap to understand that the style of bog from which one cuts one’s peat will make a marked difference to the particular flavours with which the peat smoke supplements the malting barley. Indeed, even bogs of the same style are likely to yield peat with differing flavours depending on their depth, their particular biological makeup and the place in the world the bog is found.

However, are these the factors which shape the flavours of peated single malt whisky?  Only in part – and a subsidiary part at that. Imagine for a moment that you were drinking a peated cognac, calvados, rum or bourbon. (Yes, we’re asking you to take a flight of fancy at this point.) Would their hypothetical flavours be the same as those of a peated single malt whisky? Of course not. Because peat is not the ingredient, but is an adjunct. A supplement.

It is very easy to get hung up on peat. It can make a lot of noise in a whisky; be a blunt instrument at times. But its contribution to a single malt whisky’s flavour is always secondary to that of barley – the thing from which single malt whisky is made. No amount of peat can hide, even from the most casual drinker, that the substrate is of malted barley, rather than any other sort of grain, or a fruit such as apples or grapes, just as the drinker of pine-smoked Lapsang Souchong isn’t duped into thinking they are sampling something other than tea, and the drinker of beech or oak-smoked Rauchbier wouldn’t mistake it for anything besides beer.

Of course if one is receiving one’s peated malt in bulk, with barley mixed from a wide range of farms – possibly even a range of countries – then the ingredient is as far as one can dig for the influences of flavour. But what if the barley from single farms was to be separately peated before fermentation and distillation? It is now conclusively established that the place in which barley grows – its terroir – has a significant impact upon the whisky that barley becomes. So what of the influence of terroir when peat is added to the equation?

Just as there were once those who said that terroir couldn’t exist in whisky, that its nuances and character would be destroyed by distillation and fermentation, so there remain those who believe that peated barley could not possibly retain its essence of place. We have discovered this to be yet another misconception.  Distilling peated single farm origins – many of which we have previously distilled in their unpeated forms – we have found that not only do the individual characteristics of a farm’s terroir remain, but the contribution they make to the spirit’s flavour is, astonishingly, more significant than that of the peat smoke. Logically, this of course makes perfect sense. After all, if you can taste the plant – barley – behind the peated whisky, which no one would dispute, and if the majority of the plant’s character derives from the place in which it is grown, then it is natural that the voice of its terroir would carry over the smoke. But it is one thing to reach a hypothesis, and quite another to see it confirmed by blind sensory analysis conducted by a panel of tasters in controlled laboratory conditions.

Peat is an evocative, even iconic flavour. The tunes it can play when it interacts with malted barley from different farms and terroirs are myriad and fascinating. And of course, as with unpeated single farm whiskies, they form new building blocks with which to layer more complex cuvées; additional instruments in the most orchestral whiskies.  But it is always important to remember that, where the flavours of peated whisky are concerned, it is ‘whisky’ and not ‘peated’ that is the operative word. And heartening to think that, even when wearing a cloak of peat smoke, it is the nuances of terroir that drive a whisky’s flavour…if one cares to look for them.