The Whisky Congener of Leathery is a tricky one. Why? There is no leather in the whisky production process. Well maybe the still-man wore leather clothes at one point but other than that I seriously doubt the whisky comes into contact with leather at all. In fact I am sure.
The congener is described as “leathery”, not “leather”. So it is a congener that is “like” leather, but not equal to leather.
If you want to know what the leather in your whisky is all about please take a moment to learn that leather is animal skin that has been peeled of the animal. Lets call the animal a cow. So the cow is killed and then the skin is “removed” from the meat. The skin, with left over meat and hairs, is moved to a leather tannery. Here it is “treated” in order to remove the left over meat and the hairs are removed. This is all explained in the video below.
As you will have seen the “skin” of the animal is what we call leather. If the leather is not tanned the leather will degrade and smell horribly. This is NOT the smell that was intended in the Revised Scottish Whisky Flavour Wheel.
The smell of leather actually comes from the stuff (oils / wax) we rub on the leather in other for it to not degrade. So the “leather cream” you put on your leather is the smell we have been associating with leather. I learned tons of things about leather and the video below helped me understand why taking care of your leather is so important.
What I also learned is that the “oils” used to tan and care for leather differ across the world. There is “Spanish leather“, “Russian Leather” Check out the Leather wikipedia and just see how many processes can be used to make leather. Also many plant, natural and man made oils can be used to tan leather.
So which leather is used as the main descibtor in the Flavour Wheel? Is there something like “Scottish Leather”? I just don’t know the answer to that. What did Scottish tanneries use to tan leather? I seriously do not know.
So back to chemistry. What does the “Good Scent Company say are the most used chemicals to describe “leathery“. As you can see for yourself on the link the primary chemicals that have “leathery” as descriptor are:
- 2-tert- butyl-para-cresol, Fragrance: odor: cresol, medicinal, leather,
- 6-tert- butyl-meta-cresol, Flavour / Fragrance: odor: russian, leather
- 2-tert- butyl-6-methyl phenol, Fragrance: odor : cresol, phenolic, leather, medicinal
- castoreum absolute, Flavour / Fragrance: odor: leather, smoky, animal sweet
Castoreum absolute is an exudate from the castor sacs of beavers. Yes, beavers.
You might have notices that first 3 chemicals mentioned in the list have descriptors whisky drinkers are familiar with. Cresol, medicinal, phenolic, smoky. That is because the main structure of these chemicals is a phenol ring. There is a Butyl Group added to the different positions along the phenol ring. Since these can be added to different carbons on the phenol ring the numbers change at the beginning of the chemical name.
Why then, if all the descriptors like smoky, medicinal and phenolic is leathery part of the “grainy” group on the flavour wheel and not part of the “peaty” group.
It is ( I am making a statement based on reading books) because the origins of the phenols used to make these chemicals come, most likely, from the husk, cell wall and aleuron layers of the barley. Hence the “grainy” categorisation.
Now there is plenty of room to say, based on the diagram above, that the “leathery” congener could also come from the lignin in the cell structure of the oak of the cask. But I cannot spot any butyl group in the degradation products of lignin when they degrade during alcohol reactions. (please correct me if I am obviously incorrect. I am not a chemist)
So the smell of leather is not the smell of leather, but the smell of the stuff that we use to keep leather from stinking really really bad. The stuff we use to “perfume” leather with can be made from Russian Birch Tar, Beavers excreting stuff and other oils and waxes used in for instance Spain. Which one was used in Scotland I cannot find. If I ever do I will remove this last sentence and add a link to the origins of the smell of Scottish leather.