What is PPM in whisky? (And why the number on the label can be misleading)

PPM (parts per million) is the measurement of how much phenol (smoke flavour) is present in the malted barley after peat smoking. 

Imagine 1,000,000 barley grains. Replace 2 of them with pure smoke. This represents the barley used for making Bunnahabhain (an essentially unpeated Islay). If we then replace 8 in total with smoke, we have Highland Park. Replacing 50 gives us Ardbeg, and Octomore would need 160+ replaced with smoke. Tiny numbers with huge impacts on final flavour.

PPM is one of the most misunderstood numbers in whisky. It is often mistaken for a direct measure of smokiness in the final whisky. In reality, much of that peat character is lost or shaped throughout mashing, distillation and maturation. Still shape, cut points, oak selection and even peat origin all play a major role in how smoky a whisky actually tastes. In this guide, we break down what PPM really means, why it can be misleading, and what whisky drinkers should focus on instead when choosing a peated dram.

Check out The Whisky Club's guide to peated whisky for more smoky inspiration and nuggets of information.

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What is PPM in whisky?

In a nutshell, PPM gives an indication of how much peat smoke the barley has absorbed from the drying process. The higher the parts per million phenol, the smokier the malted barley - and the more potential there is to create a smoky whisky.

One thing to note, it is not the PPM of smoke in the final whisky. This is more difficult to measure, as some cask extractives are phenols making measurement much more complicated. Occasionally a distillery will let you know the phenol parts in the final spirit (we're looking at you Meikle Toir), but the industry standard is to let you know the PPM of phenols in the malted barley.

The PPM scale: lightly peated to peat monster

PPM levels can be difficult to visualise, so let's talk about flavour. There are probably 5 levels of peat smoke that people speak about: Unpeated, lightly peated, medium peated, heavily peated and super heavily peated whiskies.

• Unpeated - 0-2ppm - these are whiskies made from malted barley that has had no contact with peat smoke. Recognisable unpeated whiskies include Glenmorangie, Glenfiddich, The Macallan and Glengoyne.
• Lightly peated - 2-8ppm - these are whiskies that use peat smoke as a way to create structure as opposed to developing smoky characteristics. Just as peated notes come over the still last during distillation, they also activate favours at the back of the tongue. Used skilfully enough, this translates to a maltiness and oiliness in a whisky. Brands like Bruichladdich, Bunnahabhain, Benromach, Oban and Glen Scotia are considered lightly peated.
• Medium peated - 8-15ppm - these are whiskies where peaty, smoky aromas are recognisable, but are not necessarily the star of the show often accompanied with coastal, briny or malty notes. Talisker, Springbank and Highland Park are two of the most famous medium peated whiskies.
• Heavily peated - 15-50ppm - heavily peated whiskies often use the smoky notes as their guiding light. You can smell these from across a room. Almost every Islay whisky sits in this category. Laphroaig, Lagavulin, Ardbeg, Caol Ila, Kilchoman and Port Ellen are all considered heavily peated.
• Super-heavily peated - 50ppm+ - this is a category entirely created by Bruichladdich when they decided to push the boundaries to create Octomore. For these whiskies, the peat can often be so heavy that it provides a backdrop for other aromas to bounce from. Brands like Meikle Toir Turbo, Ardbeg Supernova and Octomore are examples of super-heavily peated whiskies.

Weirdly the super-heavily peated Octomore doesn't necessarily present as the heaviest in flavour. This is down to the distillers and Whiskymakers making decisions to balance the overwhelming smokiness in the whisky. This can be done by taking late cut points, using active oak casks and most importantly, using mainland peat instead of Islay peat to introduce the smoke.

For more information on the types of peat available, check out The Whisky Club's guide to peated whisky. For more information on the PPM levels of your favourite Islay whiskies, have a look at The Whisky Club's guide to Islay whiskies.

Why PPM doesn't tell you how smoky a whisky tastes

Parts per million doesn't necessarily reflect how smoky your whisky will taste. This is down to a few factors. First of all, peaty aromas and smokiness is shed throughout the whisky making process. The smoke is introduced to the barley at the beginning of the process, but as it traverses the distillery, we lose smokiness as bi-products exit the system. See the next section for a detailed breakdown.

In addition, the distiller can choose to capture more or less smoke by adjusting the cut points during distillation. Peaty notes come through at the end of a distillation run, so a distiller can cut their spirit earlier capturing less of the peaty goodness.

Finally, Whiskymaker or warehouse manager can balance the smoke out of a whisky. Using more active casks will introduce more robust oaky notes. These can help tame or mask some of the peaty, smoky aromas in a glass.

A great way to experience these differences is to compare Lagavulin with Caol Ila. These distilleries use the same barley peated to the same level and have identical fermentation regimes, so until distillation, they are effectively the same. But Lagavulin's short, squat stills allow heavier, oilier notes over into the final spirit and Caol Ila's taller stills ensure more delicate, lighter smoky notes end up in the final whisky. Each distillery's maturation regimes accentuate these differences further. Lagavulin often uses more active oak casks, ensuring there is a rich sweetness introduced to balance the oily smoke. Caol Ila on the other hand, tends to spend more time in ex-Bourbon casks meaning the smokiness remains the star. It is not masked, it is elevated.

What actually determines smokiness in the glass

To understand that beautiful, pungent and complex aroma in your glass, we need to understand where in the process peat is introduced and how it is affected by the rest of the whisky making process.

Peat smoke is passed through the barley during the malting process. It then sticks to the husk of the barley and is present throughout the whisky making process. The longer the exposure to smoke, the peatier the barley and therefore the higher the PPM recorded.

• Harvest: Barley is brought in from the field and dried, ready for malting.
  Steeping: It is then soaked on and off in water for a few days to kick-start germination and begins to sprout. The barley thinks it's back in the field and wants to reproduce.
• Malting: It is then spread on a concrete floor where it continues to sprout and germinate. It will be turned to stop it matting and to prevent overheating. This process is breaking down protein walls in the grain giving the brewer access to starch which is vital for alcohol creation later.
• Kilning: To arrest the germination process, the barley is dried out. Traditionally, this would have been done with a peat-fuelled fire. These days, hot air is the most efficient way to dry the grain. Peat smoke is then injected for flavour addition only. (It is a fairly inefficient fuel for heat creation.)
• Losing smoke: The barley then carries any smoke with it through the distillery, each stage leaving some phenols behind. Typically around 75% of the phenols are left behind between kilning and distillation.
• Mashing: In the mashtun, 100% of the phenols are present, but only the wort (water for brewing) is carried forward, leaving lots of smoke behind in the draff.
• Distillation: During distillation the phenols are hydrophobic, so they come over the still at the end of distillation. Some phenols will be left behind in the wash still as part of the pot ale. Even more will be left in the feints or spent lees after a second distillation. Still shape will also have an effect. The short stills at Lagavulin allow more phenols into the final spirit. Compare this to Caol Ila, where the stills are taller letting less of the oily, smoky notes over the top.
• Making Cuts: The distiller can leave even more phenols behind by making early cuts. That is to say they stop taking the spirit before the smoky notes are over the still and in the spirit.
• Maturation: over time in a cask, aromas and flavours are lost. Some due to evaporation, others due to overpowering from other aromas and some are broken down over time. This means that some whiskies may appear less smoky after a few decades of maturation. Anyone who has had the pleasure of trying a very old Laphroaig or Ardbeg will know that the smoke is more delicate.
• Despite all of this "phenol shedding", the final whisky will still carry a noticeable smokiness. PPM might seem like a tiny measurement in the grand scheme of things, but Highland Park uses barley with a PPM of about 8, and you can definitely smell and taste the unique, beautiful influence of the Orcadian peat smoke of the spirit.

Check out The Whisky Club's guide to making whisky for a more in-depth explanation of the distillery process and The Whisky Club's guide to Casks for more insight into maturation and how it affects balance.

Not all phenols are created equal

PPM is not the final word when it comes to the flavour of a smoky whisky. Firstly there are different types of peat around Scotland, each one contributing different flavour profile to our favourite malts; secondly, there are different compounds that bring different flavours, but these are harder to quantify; and finally there is the human element. Decisions made by the distiller and Whiskymaker can alter how much of the smoky character makes its way into the final glass.

Different types of phenol

Different flavour indicators

• Phenol - this is your TCP/medicinal flavour indicator
• Syringol - this is where your bonfire-like smoke aroma comes from
• Guaicol - this brings a slightly smoky flavour to a whisky
• Cresols - that tar-like flavour in some Laphroaig is likely caused by cresols
• Eugenol - also found in cloves, this is your herbal smoke

Does peat terroir matter?

Different types of peat

• Peat from Islay brings a more medicinal smoke to the barley. Often described as old rope, tar or TCP, Islay peat is used to smoke barley at Laphroaig, Ardbeg and Bowmore.
• Peat from the mainland near Aberdeen has more wood matter and produces more of a bacon smoke. This is what they use for making Octomore, Port Charlotte and Ardmore.
• Peat from Orkney is perhaps the most unusual. The bogs are situated on clifftops in an area too windy for trees to grow. The result is a peat comprised of mostly heather. This gives an aromatic, perhaps floral smoke to Highland Park whisky.
• Peat from Tasmania is different again. Not only is it created in the Southern hemisphere, the way it is used to smoke the barley is different. It is closest to mainland peat in Scotand from a flavour perspective. At Lark, the already malted and dried barley is re-soaked so that the peat smoke can cling to the grains. An Antipodean solution to a global problem. 

How distilleries measure PPM

You might be wondering how all this is measured. The short answer is that there are two methods: UV spectroscopy and High Performance Liquid Chromatography or HPLC. HPLC is the more accurate method, and is the industry standard. Basically, a whisky sample is passed through the chromatograph generating a spectrum of peaks, each one representing a flavour compound and its concentration. Using a model, scientists can compare their results to see which compounds are present and in which concentrations. It is worth noting that higher peaks don't necessarily corelate to more pronounced flavours as each phenol type will have a different aromatic threshold. This is another reason that PPM can be a misleading number.

PPM reference guide: well-known whiskies and their peat levels

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PPM FAQs

What does PPM stand for in whisky?

PPM stands for parts per million phenol in the malted barley. It detects compounds like phenol, guaiacol, cresol and eugenol. Each one delivers a different smoky aroma or flavour to the final whisky.

Does higher PPM mean a smokier whisky?

Higher PPM does not necessarily mean smokier whisky. Distillery cut points, still shapes, cask selection and type of peat will all affect how smoky a whisky tastes. First fill casks can balance smokiness, Islay peat tends to taste more medicinal than mainland peat, and if a distiller cuts his spirit earlier, he can leave much of the peat smoke flavour behind in the still.

What is the highest PPM whisky?

The highest PPM whisky recorded is Octomore 8.3, clocking in at 309.1PPM. For context, Ardbeg and Laphroaig are around 50PPM.

What PPM is considered heavily peated?

Anything over 15-20ppm is considered heavily peated. Bowmore and Kilchoman 100% Islay sits at the bottom of this scale with Ardbeg and Laphroaig at the top. Above this we have super heavily peated whisky which is an exclusive club consisting of Octomore, Meikle Toir and Ardbeg Supernova.

Is the PPM on the bottle the same as the PPM in the whisky?

The industry standard is to quote the PPM in the barley. In the final spirit, around 75% of the PPM will have been left behind in the distillery or the cask. One notable exception is Meikle Toir, which tends to quote the PPM in the spirit.

Why do two whiskies with the same PPM taste different?

Two whiskies with the same PPM will taste different for a few reasons. First and foremost the production decisions and equipment at each distillery will be unique, whether peated barley is present or not. So the smoke is already being built upon different foundations from one distillery to the next. Secondly, the type of peat might be different giving the smoke a different character. Thirdly, the oak policy and blend makeup might be dialling up the smoke or indeed masking it. Each of these decisions will affect the flavours we experience more than PPM alone.

Does the Whisky Club feature whisky from different peat levels?

Absolutely. The Whisky Club procures whisky across the peated spectrum. Here is a flight of 5 different peat levels featured by The Club:

• Unpeated - Benromach Contrasts: Unpeated Sherry 12 Years Old
• Lightly peated - Highland Park Between You and I 16 Years Old
• Medium peated - Kilchoman Madiera 100% Islay Barley 
• Heavily peated - Laphroaig Elements 3.0
• Super heavily peated - Meikle Toir Islay Peat single cask

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