Phenol PPM Explained: What Peat Measurements Tell You

Phenol ppm is a measurement of selected smoke compounds, usually in the peat-smoked malted barley rather than the whisky in your glass. It helps describe a production ingredient, but the analytical method and what happens during whisky-making limit how confidently you can compare two numbers. A higher malt ppm figure is not, by itself, a reliable prediction of a smokier whisky.[1][2][5]

What phenol ppm measures

Ppm means parts per million. For peated malt, researchers express phenol concentrations in milligrams per kilogram, equivalent to ppm, and use the combined result as a marker of the barley’s peatiness.[1][2]

“Total phenols” sounds as though it counts everything responsible for smoke flavour. In the malt specifications described by a 2018 research paper, however, it means the sum of eight marker compounds: phenol, guaiacol, three cresols, 4-methylguaiacol, 4-ethylguaiacol and 4-ethylphenol. The three cresols are identified separately as p-cresol, m-cresol and o-cresol.[2]

These compounds have been used for decades to measure smoky character, but they are not every flavour compound present in peat smoke. Think of the result as an analytical indicator, not a complete inventory of what your nose might detect.[2]

The material being tested matters just as much as the number. St. Kilian says ppm usually refers to phenols in peat-smoked malt; Torabhaig distinguishes “in-grain phenols”, measured in malted barley, from “residual phenols”, measured in distilled spirit.[5][6] For the wider context, start with peated whisky.

How phenol ppm is measured

The conventional analysis described by researchers does not simply scan a handful of whole grains. Malt is finely ground, water is added, and the sample is steam-distilled so that the resulting liquid can be analysed using high-performance liquid chromatography, abbreviated to HPLC, or a colorimetric method.[1]

HPLC can be applied both to steam distillates prepared from barley malt and to new make spirit, meaning freshly distilled spirit before maturation. Those are different sample materials, even when the same analytical technique is used.[2]

There are two separate questions here: how well the laboratory extracts the compounds, and how the instrument or chemical test measures them. The 2018 paper warns that inefficient distillation or extraction can introduce inaccuracy before the measurement itself takes place.[2]

Why the test method matters

Claim: A colour test can mislead when measuring heavily peated malt.

Verdict: Documented

What the record shows: In their 1977 paper, Moray Firth Maltings researchers Bathgate and Taylor described the test as fairly accurate at low levels but potentially misleading at high ones. Its reagent was not sensitive to some major phenol constituents of peat smoke.[3]

Evidence against or gap: The available source is the abstract, not the full paper.

Earliest known source: Bathgate and Taylor, 1977.

Source: https://api.openalex.org/works/doi:10.1002/j.2050-0416.1977.tb06812.x.

Last checked: November 2026; day to be confirmed.

That finding does not make every colorimetric result useless. It means that a result belongs with its method, and that a figure produced by one method should not automatically be treated as interchangeable with a figure produced by another.[3]

Nor should a result be read as a promise that every grain carries the same phenol concentration. The 2017 researchers explain that exposure to peat smoke is uneven and that individual grain surfaces take up different amounts.[1] The number describes the analysed malt sample, not a uniform coating on every grain.

What counts as lightly or heavily peated?

A 2017 conference paper with a Scotch Whisky Research Institute co-author used the following working classifications for malted barley. These are that paper’s categories, not an industry-wide standard for describing whisky.[1]

The distinction between malt and whisky remains essential when reading these bands. “Heavily peated” here describes an ingredient within a research classification; it does not establish how intensely smoky a finished whisky will seem.[1][2]

The same paper explains that working levels can be created by mixing unpeated malt with very heavily peated malt, whose phenol level it gives as about 120 to 130 ppm by HPLC. A requested malt specification therefore need not mean that every batch was separately exposed to smoke until it reached that number.[1]

A 2018 paper, drawing on Bringhurst and Brosnan’s earlier work, described generally requested malt specifications as running from 0 to 50 ppm. Its own research samples extended to 124.5 ppm, described as atypically highly smoked.[2] Neither that usual specification range nor the working bands above should be mistaken for a ceiling.

What happens between malt and spirit?

Smoke-derived phenols adhere to grain surfaces and can carry through production into spirit. They do not all make that journey, and Torabhaig describes its residual spirit phenols as significantly lower than the starting value in the malt.[1][6]

The useful question is not simply “what ppm did the distillery start with?” It is also “what happened to those compounds afterwards?” The following table separates the starting material from the later measurements.

A cut point is the point at which the distiller changes which portion of the distillation is collected. St. Kilian says fresh distillate can have about 30 to 70% of the malt’s ppm value, depending on that choice.[5] This is a producer’s account, not a universal conversion formula.

Some smoke compounds may not transfer at all under the conditions tested. In laboratory peating, mashing, fermentation and distillation trials reported in Barry Harrison’s doctoral research, lignin-derived syringols did not transfer into spirit, although the resulting spirits still grouped according to peat source.[4]

That finding helps explain why “smoke compounds” and “the compounds counted by a particular test” are not interchangeable ideas. For the source material itself, see what peat is.

Why ppm cannot predict the whole flavour

The eight marker compounds provide a useful measure, but they are only markers of flavour. The 2018 researchers also explain that peat from different places changes the balance of phenols deposited on malt, which in turn influences flavour.[2]

Adding those compounds together gives a total; it does not preserve their individual proportions in the headline number. Two totals therefore cannot, on their own, tell you whether the underlying balances are alike.[2] That is a limitation of the summary, not a reason to discard the measurement.

Production adds another layer. St. Kilian’s account of cut points shows why an ingredient specification cannot stand in for an analysis of the collected spirit.[5] A malt number answers a narrower question than a description of the whisky’s aroma.

Maturation needs a separate explanation

Claim: Maturation changes how smoky whisky seems.

Verdict: Disputed

What the record shows: St. Kilian says phenol content decreases and some volatile phenols escape through the cask. Torabhaig, citing experts, instead emphasises wood derived flavour compounds softening smoky aroma.[5][6]

Evidence against or gap: The accounts differ over the role of falling phenol levels; neither establishes a universal conversion from malt ppm to mature whisky ppm.

Earliest known source: Not established from the sources checked.

Sources: St. Kilian, 22 November 2023, https://www.stkiliandistillers.com/en/blogs/wissen/p-wie-ppm-analytik; Torabhaig, 1 May 2025, https://torabhaig.com/blogs/news/peat-exploring-phenols.

Last checked: November 2026; day to be confirmed.

Those accounts should not be reduced to a fixed annual loss or a formula for converting malt ppm into mature-whisky ppm. Neither source supplies a generally applicable calculation, and a change in perceived smoke is not automatically evidence of a matching change in measured phenols.[5][6]

Reading a ppm claim usefully

When you encounter a ppm figure, first identify the sample: malted barley or distilled spirit. Then look for the analytical method and whether the description refers to total marker phenols.[1][2][6]

Compare like with like wherever the information allows. A malt HPLC result and a spirit measurement are not rival answers to the same question, while a number without its method gives you less basis for comparison.[2][3]

For choosing by flavour, use ppm as supporting information rather than the deciding score. The measurement describes selected compounds; peat source and production help determine what those compounds mean in the spirit.[2][4][5] Smoky whiskies for beginners is the next step if your question is about finding a style rather than interpreting a laboratory result.

Sources

1. Tschannerl, J., Ren, J., Jack, F., Marshall, S. and Zhao, H. Employing NIR-SWIR hyperspectral imaging to predict the smokiness of Scotch whisky. Optical Characterization of Materials, 2017, conference paper held by Strathprints.
   https://strathprints.strath.ac.uk/60344/1/Tschanner_etal_2017_Employing_NIT_SWIR_hyperspectral_imaging_to_predict_the_smokiness.pdf

2. Tschannerl, J., Ren, J., Jack, F., Krause, J., Zhao, H. and Marshall, S. Potential of UV and SWIR hyperspectral imaging for determination of levels of phenolic flavour compounds in peated barley malt. Food Chemistry, 2018, accepted manuscript, doi:10.1016/j.foodchem.2018.07.089.
   https://strathprints.strath.ac.uk/64807/1/Tschannerl_etal_FC_2018_Potential_of_UV_and_SWIR_hyperspectral_imaging_for_determination_of_levels_of_phenolic_flavour.pdf

3. Bathgate, G. N. and Taylor, A. G., Moray Firth Maltings Ltd. The Qualitative and Quantitative Measurement of Peat Smoke on Distiller's Malt. Journal of the Institute of Brewing, 1977, abstract accessed through OpenAlex, doi:10.1002/j.2050-0416.1977.tb06812.x.
   https://api.openalex.org/works/doi:10.1002/j.2050-0416.1977.tb06812.x

4. Harrison, B. Peat source and its impact on the flavour of Scotch whisky. Heriot-Watt University, doctoral thesis, 2007, repository record and abstract.
   https://www.ros.hw.ac.uk/handle/10399/2032

5. St. Kilian Distillers. P, as in PPM analysis. Producer’s account, 22 November 2023.
   https://www.stkiliandistillers.com/en/blogs/wissen/p-wie-ppm-analytik

6. Torabhaig Distillery. Dr Mike Billett on Peat: Exploring Phenols. Producer’s account, 1 May 2025.
   https://torabhaig.com/blogs/news/peat-exploring-phenols

This desk-researched article uses the site’s verified fact sheet TOP-A075, distinguishing academic findings from producers’ explanations and keeping malt measurements separate from spirit measurements.

Last checked: November 2026