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What are Phenols?
If you've glanced at our guide to chemicals that flavor whisky, you know that there are a huge number of molecules that can impact final taste. The main phenols are the namesake Phenol - iodine like or medicinal flavor, Guaiacol - burnt/smoke notes, Syringol - aroma only smoke, and Cresol - earthy tar/coal/moss.
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Where does Phenol in Scotch come from?
Most phenol in scotch is due to peat being burnt in a kiln which releases phenols into the air that then bind with the moist barley sitting above, a process which can take 10-30 hours. This is typically done to dry the malted barley thus stopping the germination process which would otherwise consume all of the wonderful fermentable sugars. Peat is a thick mass of partially decayed organic matter, typically vegetation such as moss and grass, that forms in acidic conditions without the presence of air (anerobic). The more time that the new green malt sits exposed to the peated fire, the higher the resulting phenol level will be. Producers will have an idea for what phenol ppm they want to achieve. Maltsters will commonly blend various malt batches to achieve the right ppm concentration as the phenols are absorbed somewhat inconsistently by each batch due to difference in moisture and peat quality. Since the phenol primarily comes from peat, there are also a number of non-peated scotches on the market that allow for the highlighting of more subtle floral or fruit flavors. They will still have some small level of phenols from other sources but you'll typically see these in the 0-5ppm range. Phenol ppm measurement is done on the malt prior to mashing, fermenting, and distillation and is an accurate measure of how peated the malted barley is but other factors later in the process will significantly impact how much smoke flavor is present in the final product. The total amount of phenol typically decreases over time due to evaporation with the impact that super aged whisky would need to start at a much higher ppm to retain the same peated punch at maturity. While it may be tempting to assume that some smoke flavor comes from the charring of the barrel or Scotland's water, neither of those sources contribute significantly to the phenol concentration of a scotch.
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Phenol PPM in Scotch Regions
Though again there are many factors that impact the final smoke flavor and peat content, we can generally describe the malt entry phenol ppm ranges for the major scotch producing regions as follows:
- Islay - High Peat: 40-55ppm for distilleries like Laphroaig, Lagavulin, and Ardbeg
- Islands - Medium Peat: 20-25ppm though there are some unpeated expressions
- Campbeltown - Medium Peat: 20-25ppm though there are many unpeated recipes
- Highlands - Low Peat - 1-3ppm, low enough that many may not notice.
- Speyside - Low Peat: 1-3ppm
- Lowlands - Unpeated: 0-1ppm
These are the most general of guidelines and final phenol content can range by up to 60-80% from the initial concentration. Some producers may have both peated and unpeated offerings as well. Lastly, the chemical composition of peat differs dramatically between the whisky regions which will result in different concentrations.
Phenol Content of Common Scotches
Here is a consolidated list of ppms from a variety of sources, but many producers do not publish these online so YMMV.
- Ardbeg: 50-55ppm (10 year), Supernova 100ppm
- Ardmore: 15ppm
- Benriach - 45ppm
- Benromach: 10ppm
- Bowmore: 25ppm
- Bruichladdich: 4ppm
- Bruichladdich Octomore: (80-160+ ppm depending on edition), Octomore 8.3 was 310ppm
- Bunnahabhain: .5-2ppm
- Caol Ila: 35-38ppm
- Glen Scotia: 12-15ppm
- Glenfiddich: unpeated except for fire and cane
- Glenmorangie: unpeated
- Highland Park: Earthy and Floral 12-15ppm
- Kilchoman: 20-40ppm
- Macallan: unpeated
- Laphroaig: 35-45ppm, typically drops to around 10ppm over 10 years, Floor malted 80ppm
- Lagavulin: 32-37ppm, shares the same malt as Caol Ila
- Port Charlotte: 40ppm
- Springbank: 12-15ppm, 50-55 Longrow
- Talisker: High in phenol iodine character 14-16ppm
- Tomatin - 15ppm
Conclusion: Phenols and Smoke
The malt phenol ppm content is, at best, a directional indicator of flavor. The quality and content of the peat, temperature and duration of kilning, type of cask used, and duration of aging all have an outsize impact on the final smoke flavor of a whisky. You can be sure though that unpeated or low initial phenol whiskies will be relatively mild. If you're a bourbon drinker, low ppm and unpeated scotches are a great place to start. Why not try something at each level of the peat spectrum?