The Magic and Mayhem of Whisky Phenols
Peated whisky. Some people love it and some people loathe it. Does it taste like lovely silky campfire smoke to you, or an ashtray? Whatever you think of them, they are probably far more complex than you thought. Read on for a short discussion of the phenols behind peated whisky.
What are Phenols?
Think of those famously smoky Islay drams and your mind may turn to the PPM (parts per million). This is a measure of the phenols in peated whisky from burning peat during malting. Simple right? Burn peat to smoke the barley and you get smoke in your whisky. As with almost everything in whisky, it’s not quite that simple. Yes, phenols in peated whisky are created by the decomposition of organic matter by heat (burning), but gets more complicated. There are a few important things to note:
- Not all phenols are from peat.
- There are many different phenols in whisky.
- Not all phenols are smoky.
Not all Phenols are from Peat
Peat is not the sole source of phenols in whisky, but they all come from burning plant matter. Plants are made up of lignin, cellulose and hemicellulose and different plants having different percentages of each. Lignin is the primary source of phenols though the others can contribute flavour to whisky once burned.
There are three plant-related things that are typically burned in whisky making:
- Coal (Anthracite)
- Oak casks
Coal originates with plant and other organic matter. Anthracite is 92.1 to 98% carbon, and is therefore not a significant source of phenols. After centuries of heat, pressure and decomposition, virtually all lignin and cellulose have disappeared.
Likely the most famous source of smokiness in peated whisky and the biggest contributor to phenols in your dram. It is particularly responsible for the more intense phenols.
It is well known that oak casks are usually charred or toasted. However, it is less commonly appreciated that charring oak also creates phenols that will flavour the whisky during maturation.
What about the Water?
The mash water for some whisky flows through peat bogs, but this does not contribute smoke to your whisky. Peat does not smell or taste, smoky or even what we call peaty, because it has not been burned. The peat traces in your mash water may add some flavour to your wash, but it is more sweet or earthy than smoky.
There are Many Different Phenols in Peated Whisky
‘Phenol’ is one molecule and ‘phenols are the family of molecules. They all have the basic phenol structure but they can have other ‘functional groups’ that change their properties. These properties include flavour and aroma.
Exactly which phenols appear in your whisky, and in which proportions, depends on many things. This includes:
- Temperature at which the organic matter burns. Is it a smouldering peat fire under your barley or a hotter fire?
- Amount of oxygen present. There is typically more oxygen available when a cask is being charred than in a smouldering peat fire.
- Composition of lignin, cellulose and hemicellulose. This differs between plant species, and therefore between different peat sources
- Exact structure of the lignin. Again, this differs between plant species.
- Age of your peat. Lignin transforms to humic acid over time, which still provides phenols, but different types.
These factors create a diverse palette of different phenols. And it’s fair to say that determining exactly how each factor contributes to the concentrations of each particular phenol is extremely difficult. For the purposes if this article, we’ll just say “it’s complicated”. Nonetheless, some of the phenols in peated whisky are relatively well known and are presented below. It is certainly not an exhaustive list.
This is the basic unit and simplest molecule in the family. Phenol has a medicinal or antiseptic aroma and it actually is an antiseptic historically used in surgery. It’s also quite toxic, but the concentration in whisky is not high enough to cause harm.
Syringol and Guaiacol
These have closely related structures but are a bit different. Syringol has a bonfire-like smoky aroma, but no flavour, guaiacol has a pure bonfire-like smoky flavour, but no aroma. They are often found together but not always. If you’ve ever had a peated whisky with a smoky aroma but not flavour (or vice versa) then it’s likely due to differing percentages of these two. They are also the key components in ‘liquid smoke’, which you can buy from barbeque shops.
If you can’t get enough of that thick tar-like note found in some peated whisky, then this is your hero. Or rather these are your heroes, as there are three cresols. They are romantically namely ortho- meta- and para- cresol and have similar structures, tastes and aromas.
Xylenol is still somewhat medicinal, but a little sweeter than those discussed above. Like phenol, xylenol is also a disinfectant and like cresol, can be extracted from coal tar. It is a common food flavour additive.
Not all Phenols are Smoky
Believe it or not, this is a phenol. In whisky it is largely derived from American oak casks and is created through charring. Exceptionally important to Bourbon, there is still some left to extract from the charred staves once other whisky makers get their hands on them.
Eugenol is another non-smoky phenol and one you may have found in a dram or two before. It has the taste and aroma of cloves and in fact clove oil is approximately 80% Eugenol.
Relationship to source
Of the phenols described above, the smoky ones are more likely to be derived from peat, and the others more likely to be derived from charred oak. This is not a hard and fast rule, with syringol and guaiacol notably derived from both peat and from charring.
Peated whisky and the phenols responsible makes for a complicated subject. Obviously there’s a lot more to be said and this article possibly raises more questions than it answers. Hopefully it has still managed to answer some questions about where they come from and why peated whisky tastes the way it does. Understanding the different phenols in peated whisky also allow us to be more nuanced and concise in our descriptions of flavour and aroma. For some of us geeks, at least, this contributes to our enjoyment of whisky.
Do you love or hate peated whisky? I’m keen to hear what you think. Reach out – you can read more more about me here or click on my social media icons below.A