The Chemistry of Single Malt Whisky
Posted on July 6, 2016
The wonderful world of single malt whisky has mesmerized me for the last 12 months. I joined a serious whisky club called SMUG (Single Malt Users Group) and for some time was the only female amongst a brooding group of whisky loving gents. As a result I have learnt a lot about this amazing beverage, and about my own palate. About four years ago I was converted by some sherry whiskys, I loved delicate fruit and oily palate weight, but slowly the gentleman have me warming up to the smokey character that whisky is so famous for. They have also taught me why spitting and adding water is a cardinal sin.
As a reuslt I have tried to rate them more objectively than most. I know what I like, but I will often rate something higher despite the overwhelming peat, if I can see that the single malt whisky in question is made well and achieves this level of balance between oak, terroir, smoke, alcohol and finish. It is a complex beverage, with countless factors that are governed by the distillery, the oak barrel, the place of origin, rather than the vintage and growing techniques. For this reason distilleries have very little rules compared to your Bordeaux, and the industry is constantly evolving with independent bottlings or rare special releases. The price these can fetch make it very hard to keep up with new trends or taste them all, and this element of surprise has taken my wine trained senses on a roller coaster ride into the unknown.
Understanding Whisky Chemistry:
• Whisky Lactones:
1. Whisky lactone is key to flavour
2. Wood only based includes the cis-form vanillin and coconut
3. Trans-form (mirror image of the same) has spicy, herbal elements.
• Phenols have 3 types;
1. Cresols, musty, coal, medicinal taste
2. Guiacol, burnt lignin in wood, smoky, cough syrup, bacon
3. Eugenol, bitter clove, cinnamon, nutmeg, clove, basil anaesthetic character.
• Aldehydes have 3 main types;
1. Vanillin (combined from Eugenol and Guaiacol)
2. Furfural, almond, grainy, and darkens with oxygen
3. Hexanal, grassy and furry character.
o Functional group, mostly fruity like banana, pear, sweet apple
o Principally targeted during chill filtering.
• Other compounds
1. Diacetyl, butterscotch character, or truffles
2. Sulfur compounds including burnt, rubber, meaty tones.
In a single malt whisky it is the combination of phenols along with the whisky lactone, pictured below, which gives it the unique taste. They first used peat to cook barley in the whisky distillation process because there were not enough trees to burn! This has created the key peaty character in a whisky, from the phenol compound group. Humans can only taste up to 80 ppm (parts per million) in levels yet some distillers still strive to achieve higher levels than this.
Kilkerran Cask Strength Bourbon Barrel 54.1% v/v Glengyle
Aromas are rugged, with slight cheese smell, ash, gripping nose and smokiness*. The palate is lovely and smooth with sweetness first, finishing hot yet somehow balanced. *More of the guaiacol compound – the burnt, smoky or bacon character in whisky. My Score: 8 Group Score: 8.1
Kilkerran Sherry Wood 46 % v/v
The nose is much more subtle due to lower alcohol, fragrant orange, cinnamon, honey, marzipan even. This carries to the palate, with an orange note almost px sherry like, sultanas and treacle. There is a surprising heat on the back, with great mid palate and smooth finish. Softer flavours coming from the higher levels of eugenol or vanillin, also adding to the glycerol or oily mouthfeel – both usually resulting from more time in barrel. My score: 9 Group Score: 7.7
Springbank Aged 16 Years, Local Barley 54.3% v/v
Smoke overwhelms my nostrils, but palate imitates this and I am finding that the cresol compound associated with smoke and bacon is quite high. This whisky was high in medicinal “Cresols” with small amounts of the guaiacol or bacon, partly why my score is lower. My Score: 7 Group Score: 8
Cadenhead Small Batch Aged 29 Years, 50.1% v/v, Ben Riach
Herbal notes, very coffee like, liqueur, with more esters than any other whisky from this evening. I love the fuller palate, richer flavours, with the long, tingly and slightly burning finish. This has been created from a mixture of distillations, along with Speyside (honey, grassy, sweet notes coming through). For this reason I think that this whisky was very high in hexanal lending the herbaceous note and high in esters with fruity sweetness. The complexity of these volatile aromas is why in my opinion this scored so highly, becoming the highest rated whisky of the night. My Score: 9 Group Score: 9
All in all my scores were very close to those of the group average (calculated using Sweedish rounding). What I loved most about this single malt whisky tasting was talking about the whisky chemistry discussed prior, which means I could then look at each whisky and ascertain which chemical compound was mostly at play here. Just another area of aroma chemistry yet to learn as I go further afield in taste exploration!