phenolic-compounds
Phenols

What are the phenols that are in Whisky? Do the phenols in peat explain the peat smell on a peaty whisky? How does the peat get into the whisky? I have no idea! I want to know! For Peat’s sake! (I like that word-joke).

I choose not to google this, but to look in scientific papers and see what can be found. Ok, I used google to find the articles! Bite me already ok 😉

The first paper I look in comes from the journal of the institute of brewing, volume 107, No.5, 2001 “Origins of Flavour in Whiskies and a Revised Flavour Wheel“: a Review By K.-Y. Monica Lee, Alistair Paterson* and John R. Piggott.

Phenols are, according to wikipedia :

Phenols, a class of chemical compounds that include phenol.

So Phenols are not just Phenol, but apparently also other compounds.

The wikipedia site lists a number of Phenols that sound familiar.

  • Capsaicin :
  • Carvacrol :
  • Cresol :
  • O-Cresol : Medicinal
  • Estradiol :
  • Eugenol : Spicy (clove)
  • Gallic acid :
  • Geraniol : Floral (Artificial – scented, perfumed)
  • Guaiacol (2-methoxyphenol): Burnt / Smoky
  • Methyl salicylate :
  • Raspberry ketone :
  • Serotonin / dopamine / adrenaline / noradrenaline :
  • Thymol:
  • Tyrosine:
  • Sesamol:

Some of these “phenols” are definitely not in Whisky, but they are a Phenol.

Guaiacol is the one that makes the “Burnt / Smoky” nose!

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Guaiacol “Burnt / Smoky”

According to the article The Peaty Character is called Group A. Where group A is subdivided into :

 

A. Peaty character

A.l. Burnt: tarry, sooty, ash

A.2. Smoky: wood smoke,  kippery, smoked bacon/cheese

A.3. Medicinal: TCP, anti septic, germoline, hospital

Honestly some of these descriptors don’t tell me anything. Burnt I get, ash I get to. but “Hospital”. I have been to many hospitals and most smell differently from the next. I think this is a poor descriptor. So according to this A.1 and A.2 are explained by the presence of Guaiacol in whisky. The A.3 is explained by o-Cresol.

The article lists a number of origins for these descriptors being:

Smoky: linked to degraded wood carbohydrates – cellulose, hemicelluloses and lignin’s.

Peaty: attributes originate in smoke, introduced into the airflow during the kilning processes from phenolic compounds:

  • Pyridines : Wood extractive
  • Thiazoles : Wood extractive, result of Maillaard Reactions using sugars from the barley or sugars in the wood.
  • Phenol : Lignin – derived aldehyde transformations, polyphenols from the Husk, Cell Wall, Aleuron layer of the barley. Adsorption of phenols from peat reek smoke on the outer layers of the barley.
  • Cresol (m-, o- p-) : Lignin – derived aldehyde transformations, polyphenols from the Husk, Cell Wall, Aleuron layer of the barley. Adsorption of phenols from peat reek smoke on the outer layers of the barley.
  • xylenols
  • p- and m- ethyl phenol: Lignin – derived aldehyde transformations, polyphenols from the Husk, Cell Wall, Aleuron layer of the barley. Adsorption of phenols from peat reek smoke on the outer layer of the barley.
  • Guaiacol: Lignin – derived aldehyde transformations, polyphenols from the Husk, Cell Wall, Aleuron layer of the barley. Adsorption of phenols from peat reek smoke on the outer layer of the barley. Need Vanillin to transform into Vanillic Acid before it can form.
  • Methoxy-phenols such as vanillin are also a Lignin – derived aldehyde transformation.

Phenols and other compounds that are unique to Peat smoke drying of the malted barley are adsorbed on the outer shells of the barley. This means the outer layers of the barley are “coated” with peat smoke compounds, which include phenols. I underlined “that are unique” because burning other materials such as coal also produces smoke. Flavour components are also in that kind of smoke, but some are unique to Peat. Don’s ask me which ones are. That is another question to answer.

Phenols are hydrophilic which means they attract water or can dissolve in water. So any phenols that are in / on the barley are also able to be found in the grist, husk or flour and get dissolved in the hot waters during the mashing.

I could not find any information how phenols get through the distillation process in this paper by K.-Y. Monica Lee, Alistair Paterson* and John R. Piggott. I could find many patents on how to get the phenols out of (waste) water using distillation. This would counter that the phenols from the peat make if from the wash to the final distillate. So I had to check the textbook “Whisky: Technology, Production and Marketing” to find the answer.

It says (quote):

With peated malts the spirit produced reflects a marked concentration of steam-volatile phenols, whose arrival in the spirit tends to concentrate towards the end of the distillation of the middle cut as the water to alcohol ratio alters with decreasing strength, favouring the entrainment of the phenols. To enhance the phenol concentration in the new spirit a lower strength cut point can be used, but not at the expense of producing a feinty spirit.

So not all phenols make it, just the “steam-volatile” ones. That is interesting. It is the phenols that are dissolved in the water that are “entrained” to the spirit during the later end of the middle cut, as the alcohol levels drops.

What did I just learn? (not everything is in the text below)

  • Burning Peat produces all kinds off flavour compounds including (volatile) phenols unique to peat.
  • Peat is used to dry the malted barley not because it is a heat source but a flavour compound source.
  • Some of the flavour compounds are adsorbed on the outer layers of the Barley (husk).
  • Some of the flavour compounds are absorbed in the Barley.
  • Smoke absorption in the barley is maximal at 15-30 % moisture level.
  • Raising kilning from 400 to 750°C yields several-fold increases in phenol and cresol, reducing guaiacol. So playing with the kilning temperature affects the outcome.
  • The phenolic flavour compounds are water dissolvable. This is how they get from the barley, thru the milling into the mash.
  • From the mash they make it to the wash.
  • The wash is distilled and only the “steam-volatile phenols” make it into the final distillate, depending on when the middle cut is ended.
  • The phenols in the new make spirit interact with the lignin degradation products in the wood to form the “smoke-like” smell components we all know. So next to “peat-steam-volatile phenols”, the “charr” of the barrel also adds to the “peaty-ness” of a dram.

So, the more you let the phenols in at the beginning (by burning the peat), the more they can get thru the process (steam-volatile phenols and by selecting the cut-point), the more they can interact with the lignin in the wood. Increasing the lignin breakdown in the wood can be done by (re)charing.

I also learned that the smokey character of a whisky does not HAVE to come from the smoke. The smokey character is actually a barrel wood lignin degradation product, just like Vanillin is.

The unique flavours that are imparted on the barley by burning peat make the difference in the way that some of the chemicals are added to the mix. Some result in flavours that have nothing to do with smoke or ash. So saying that a peaty whisky also needs to smell like smoke is not true. If the lignin in the wood the cask is not (re)charred it cannot degrade in the same way as a charred barrel would.

Would some of the Octomore whisky’s by Bruichladdich be explained by this? Peat yes, but no smoke? Think if you can spot an Octomore made in French Oak, American Oak. Try to find it it was charred or not.

Does our brain smell “peat” because of the “smoke equals peat” association our brain makes when the label says PPM or even just the brand name “Laphroaig”. Interesting no? Made me think!

 

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Barley
process
From Barley to Flavour Compounds
figure4
From Lignin to Vanillin and Guaiacol (Burnt / Smoky)

 

 

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