What is peat?

Peat is formed from dead, partially decayed organic plant matter that’s often built up in peatlands over millennia. The wet, acidic, low oxygen conditions of peatlands slow down decomposition, trapping this organic matter. These peatlands grow at roughly 1mm a year or 1m over 1,000 years; as such, the speed of replenishment is exceedingly slow. 95% of all peat is found in the Northern Hemisphere and, of that, almost 25% is found in Europe.

The plant life that contributes to the organic content in peat is largely based on mosses. Many different species thrive, but the sphagnum bog-mosses dominate. Growing in an almost continuous tussocky carpet, they can soak up to eight times their own weight in water, producing a deep, bouncy sponge underfoot. As well as common species like feathery bog-moss and cow-horn bog-moss, there are rare species such as rusty bog-moss, Austin’s bog-moss, and golden bog-moss. Amongst these cotton-grasses, deergrass, ling and cross-leaved heath can be found, and occasionally wild cranberry and bog orchid.

Thinking about the exotic botanicals used to compound Scottish gins: peated whisky has an equally impressive – if less-deliciously named – assortment of flora within it. The diversity of plants is fundamental to the complexity of peated aromas in whisky, no doubt one of the reasons that peat is seen as irreplaceable as a flavouring medium.

Below the active growing layer there are two other important layers for whisky production. The acrotelm is the free draining layer of highly organic matter which meets the deeper catotelm layer close to or at the water table. The acrotelm is the favoured layer for flavouring whisky, as it is free of some of the funkier flavours associated with the waterlogged and anaerobic environment of the catotelm. The acrotelm is particularly smoky especially at the lower temperatures at which it is burned to infuse flavour into malted barley.

The catotelm is the layer that, once dried provided a more powerful heat and was traditionally used for heat and energy widely in times gone by. The division between the brown drier acrotelm and the darker waterlogged catotelm can clearly be seen on the lead photo.

Sphagnum Moss from the growing layer of a peat bog.

Do different peat sources produce different flavours?

Almost certainly yes. Within individual peat bogs there can be significant differences in flora depending on location and water levels. “Raised bogs are discrete domed peatlands, whereas blanket bog covers entire, usually upland, landscapes… …These habitats do not always occur in isolation. Many areas of upland peatland comprise complex habitat mosaics, with adjacent areas of blanket bog, wet heath, pools, flushes, springs, rock exposures and acid grassland which may interact hydrologically.” – Peatland Biodiversity.

What I cannot find in the academic literature is reference to peat being coastal and containing sand, seaweed or salt, which is interesting, as a number of venerable whisky magazines and blogs have made the claim. It has a similar ring to the suggestion that costal distilleries develop a coastal character from the proximity to the sea water and salty air even when the casks are matured in central Scotland. I think it sounds like a romantic notion without substantive evidence.

A small peat bog near Burn O’ Vat, Royal Deeside

Is peat sustainable?

Peat is extensive; when considered as a volumetric resource, it is unlikely to run out. However, it is currently viewed as a favourable carbon sink which locks away carbon for longer and effectively than forestry. The use of peat and the obvious destruction of a valuable carbon sink is becoming more controversial. So, whilst it is unlikely to run out, a ban or restriction on the use of peat as part of global carbon reduction targets is much more likely.

Some of the most ecologically conscientious distilleries such as B-Corp Bruichladdich or green newcomers Ardnamurchan are still using plenty of peated malt. It should be acknowledged that peat use in whisky is significantly below the use in domestic and professional horticulture. Horticulture accounts for 1.2m tonnes of peat each year, of which 25% or 300,000 tonnes of peat comes from UK peat production operations. Whisky distillers account for about 1% of that UK total, so perhaps 3,000 tonnes.

A distillery such as Kilchoman uses around 20kg of peat to malt 4 tonnes of barley to 15ppm, adding up to about 2 tonnes a year in its own maltings on Islay. On the horticultural front, a voluntary move away from peat use in the domestic home market completely failed, despite alternative products being available; a full-scale ban seems to be on the cards.

The gardening world can substitute peat with a wide range of alternatives that include wood fibre, composted bark, coconut husks, sterilised soil, vermiculite, grit, and manure. More unusual products included composted bracken and sheep’s wool. That’s bloody excellent for the rose beds, but currently there is no replacement for peat when it comes to whisky. So perhaps the best way to preserve peat for use in whisky production is to avoid using it in horticulture? Other indirect threats to peat are through land-use changes such as drainage for forestry.

In Scotland, peat extraction permits are granted much the same way as other mineral extraction. Some sites have been active since before 1949. However, the Scottish Government does not retain a central register of peat sites, leaving the administration to local councils. A recent review of commercial peat production found that there were 14 active commercial sites in Scotland from 86 total sites, but just nine of the total sites had peat restoration plans and none of those 9 plans reached the current benchmark for peatland restoration. Only one site has had renewal of production rights refused. It seems to me that if peat is to continue to contribute to the flavour of whisky, the regulation of it’ production requires significant overhaul.

Why is peat used?

The use of peat to malt barley occurred originally because it was a ready source of fuel to isolated communities and distilleries. Gradually coal and oil replaced peat as an energy source and now peat is usually added as part of the process to impart flavour rather than providing the bulk of the energy for the malting process. As mentioned above, there is really no substitute for the complexity of flavours imparted by smoking peat.

What is PPM?

The application of peat as a flavour is now a precise science that can impart a specific level of peaty cyclic aromatic phenolic compounds into a malted barley product. The “peating” occurs at commercial maltings, or in house, where the distillery has onsite maltings. This is expressed in terms of ‘ppm’ (parts per million), with 1ppm equivalent to 1 milligram in a litre, or 0.001%.

A ‘peating’ level of around 10ppm is considered lightly peated, and typically results in a malt whisky with gentle wafts of smoke, examples being Springbank and Glengyle at about 7 to 8ppm. Around 25ppm is a medium level such as Talisker which is between 25 to 30ppm. Malt whisky with a level of 40 to 50ppm or higher is considered heavily peated; this would include Ardbeg at >52ppm, which averages about 54ppm and generally delivers much more pronounced smoke. However, with certain peated products such as Octomore from Bruichladdich the PPM can be as much as 175ppm. (Specific distillery figures: Misako Udo, 2006)

How important is PPM to the flavour of a whisky?

The average human nose can detect 1ppm of most phenols, so understanding the phenolic levels is certainly a useful measure as a general benchmark, but it does not tell us much. Is the PPM figure quoted related to the parts per million measured in the malted barley, or the finished spirit? And for that matter, how does PPM influence flavour over time?

As whisky ages we find that the peaty smoke flavour changes and falls away. It has been argued that the other flavour compounds are interacting with each other, and oxidising, in a much more complex way that allows them to become more prominent that the peat over time. In either case the original PPM figure as a measure of peatiness is a poor yardstick.

What other factors contribute to the smoky flavours?

Lagg distillery have been busy doing quite a bit of geeking out and have written a blog and organised some really interesting podcasts. In summary, the final flavour of whisky is much more closely linked to the various stages of production than you might think. Firstly, the smoke from the peat will have adhered to the husk of the grain, so the milling process is important to retain more husk for a smokier flavour.

The mashing process, and techniques such as raking the mash, or creating a cloudy wort can improve the smoky flavour carry over. The longer the fermentation the less of the phenols survive the process, so shorter fermentation will typically give a smokier spirit, though this is not always borne out. Limiting the reflux within the still by using wider squat stills and running hotter quicker distillations can all help these heavy oily flavour compounds carry over into the distilled spirit. The cut point between the middle run and the feints should be run deeper to a lower ABV than perhaps unpeated spirit would have been traditionally, again to help these complex compounds make it over the Lyne arm and into the finished spirit.

Cask ageing is also crucial, as the volatile phenols dissipate slightly with age as other competing flavours develop in the barrel over time. They type of cask used will also significantly impact the flavour of the whisky; often more powerful casks such as first fill sherry and red wine casks are used with peated whisky to create forceful flavour combinations. You can see that a quoted initial PPM of a batch of barley is then subject to an incredible number of variables before the whisky ends up in your glass.

What flavours can be developed from peated barley?

Chemically the flavour compounds in whisky can be isolated and identified and these are fantastically presented in the diagram below:

Focussing in on the phenolic flavours from peat: Phenol, cresols, xylenol, eugenol, Syringol, and guaiacol contribute most in terms of contribution to flavour, and are all examples of phenolic compounds. Guaiacol contributes to smoky flavours in coffee, and in smoked meats. In whisky it can contribute earthiness, smoke and some medicinal notes. It is required in very small quantities to have an impact on flavour. Xylenol can be extracted from coal tar and has a similar note.

Compounds called cresols are responsible for the “medicinal” notes in peated Scotch. The particular compound responsible is meta-cresol, traditionally used in sticking plasters as an antiseptic, creating an association with medicinal aromas. Cresol may also give aromas of tar and asphalt. Eugenol is also present in many whiskies, a compound more commonly found in cloves, and partly responsible for their spicy aroma. Syringols, linked to woodier content in the acrotelm, bring sweet, spicy vanilla although I am unclear how a palate would distinguish these from those imparted by the cask itself.

How does all of this transpire in practice? well let’s taste some peaty drams….

This first bottle was donated and split as a charity fundraiser by whisky-couple Whisky Click, but would almost certainly cost a few hundred quite at auction. The bottle photo is theirs, too.

Port Askaig 1982 13 Years Old – Review

43% ABV. Unknown PPM (believed to be Caol Ila) bottled for the Master of Malt.

Colour: Pale straw.

On the nose: Heavy presence of peat delivering the whole range of peated notes. Firstly, damp and vegetal with some damp cardboard notes from the time in the bottle, then warming spiced peat which then gives way to prickly industrial smoky peat, soot, coal furnaces that are reminiscent of modern Springbank and then finally medicinal iodine and antiseptic. Behind the peat there is sweetness ripe pear, cloudy apple juice, a hint of pineapple, then graphite pencil shavings.

In the mouth: Moderate sweetness, a flash of damp cardboard before a little fruit and then spicy peat. A little dry chalkboard duster, the apple is sweet stewed apple. There is some thin toffee, a little more vegetal peat, some fermented over-ripe fruit, a little vanilla and some gentle wood spices the finish is accomplished and brief leaving a little wood spice on the edges of the tongue.


Hard work to get the best out of this dram. I used a 1920s blenders glass to accentuate the aromas from the 43% ABV spirit. Opened not a month too late, as the damp cardboard notes could overwhelm the original character before long. Whisky from a bygone era, perhaps best characterised by the sheer range and depth of flavours which are significantly different from the Ardbeg 10 (below) despite having the same source for the peated malted barley.

Score: 6/10

Ardbeg 10 Years Old – Review

Non-chill filtered and naturally coloured. 50ppm Malted Barley. 46% ABV. £43.

Colour: Pale straw

On the nose: Immediately vegetal peat, grist, yeasty dough, struck flint, runny honey, boiled sweets, cinnamon, hoppy scotch ale, buttered toast.

In the mouth: Smoky ashy peat. Quite a thin mouth feel; sweet peat spices, baked apples, and wood spices all harmonious on the midpalate. Drying ashy peat and peppery spirit on the finish, sawdust and chewed HB pencil tops and traditional wooden pine school desks, damp rugby kit with a whiff of deep heat.


This delivered a few flavour memories of school rugby games, which was a lovely period to reminisce about. This Ardbeg stands up to its reputation of great value for a flavourful whisky. The vegetal flavours made me think the peat bog could be particularly damp, but then most Islay distilleries use the Port Ellen maltings which in theory would deliver a consistency of peat. Therefore, the flavour must develop as part of the whisky making process itself.

Score: 6/10

Kilchoman 100% Islay Single Cask PX Sherry – Review

27/05/2015 to 26/06/2021. 20ppm Malted Barley. 58% ABV. £92.

Colour: Deep bronze.

On the nose: Sweet sherry and smoke, some rich dates and dried figs, dark chocolate studded with smoked sea salt, bruised apple.

In the mouth: Furniture polish, waxed oak, smoky treacle toffee, rich spicy peat and smoked almonds, dry cocoa powder, dark chocolate brownie with chilli, some fruit on the finish which leaves with a salty smoky finish.


A different proposition of floor malted barely at Kilchoman itself. This is integrated peat and sherry. A little spice from the peat, but nothing too powerful. Overall, the smoke is the key flavour with the sweetness from the sherry. Very approachable despite relative youth and high ABV. Delicious example of peat and powerful casks working together.

Score: 7/10

Lead photo source: Islanders fear peat cutting ban

Acroteim and Catoteim diagram source: http://www.ipcc.ie/a-to-z-peatlands/blanket-bogs/

Chemistry of Whisky diagram source: https://www.compoundchem.com/2015/03/31/whisky/

Ardbeg 10 photo courtesy of www.ardbeg.com

Kilchoman 10 photo courtesy of Aberdeen Whisky Shop.

CategoriesSingle Malt

Graham is at the consumer end of the whisky world; constantly seeking out a bargains and generally very cautious with his limited budget. An occasional visitor to distilleries and a member of the odd whisky club. He does not collect whiskies but has a few nice ones put away for some future special occasion. He enjoys discussions with the wider whisky community and may resemble the ‘average’ Malt reader.

  1. John says:

    Lovely article, Graham. This is something I’d love to read a few times just to digest it better. Just curious if you’ve read this paper called

    Composition of Peats Used in the Preparation of Malt for Scotch Whisky Productions Influence of Geographical Source and Extraction Depth

  2. Rich says:

    Excellent work. I very much enjoy your articles and the thought and attention to detail which they include. Always a pleasure to be educated further – keep it up!

    1. Graham says:


      thanks for taking the time to comment. I take the approach that if it interests me, it’s bound to interest others too. I really learned a lot from researching this article.



      1. Larry Cush says:

        Hi Graham, was very interested in your article.I have a un harvested natural Costal Peat Bog in Coastal Washington state usa. I am trying to understand which material is best for the peated whiskey? Acrotelm or Catotelm locations. my bog has about a 12 inch root matt, then a more composted peat layer down to 3 ft. then im at the water table. The peat below that has a more distinct smell. it is estimated the bog is over 40′ deep. Any advice or direction would be appreciated. best wishes Larry Cush

  3. Shomeet says:


    Another great educational article, thank you so much.

    Wonder if you can help clarify something for me. While on tour at Ardbeg, we were told (Paraphrasing of course) that Ardbeg 10 is more peaty than an Octomore. As the method of measurement of PPM is different between the two distilleries, apples and oranges essentially. But if measured the same way Ardbeg wins? Question is: did you learn about different methods of measuring PPM? Or are they referring to measurement of PPM in the distillate (Ardbeg) Vs Malted barley (Octomore). Unfortunately at the time of hearing this, I did not have the knowledge of PPM measurement, so I didn’t inquire further. But since then, I have been learning and trying to figure it out. Or maybe, I just got it all wrong!

    Great article, thank you. Will be reading again to further geek out on.


    1. Graham says:


      Thanks for dropping in. I’m not sure that everything distillery guides say is correct. So always worth taking that with a pinch of salt.

      I cannot give you numbers for the in-bottle PPM from either distillery but Ardbeg’s Barley is malted to about 54ppm whereas Octomore barley is malted to is 90-130ppm with divergences as high as 175ppm I think.

      I think it’s unlikely Ardbeg is peatier on the palate that Octomore but I recommend a comparison if ever you find both in a bar. Please report back!



Leave a Reply

Your email address will not be published. Required fields are marked *