All about aroma

Scientist and SMWS member Aidan Kirkwood has had a lifelong fascination with aromatics, which has led him to explore exactly what’s going on to create the powerful flavour associations from our glasses of whisky. As he explains to Tom Bruce-Gardyne, it’s all about chemistry and compounds – and context

While studying bio-medical science at Edinburgh Napier University, Aidan Kirkwood’s dream was to work for a perfume house. He had a part-time job in a menswear shop and says he “was able to identify which fragrances people were wearing, which used to freak them out a bit”. It was a skill he had picked up as a teenager wandering around perfume counters trying things on. Clearly, he has an impressive nose.

Applications were made and rejections followed. It’s not easy breaking into the likes of Chanel, which pushed Aidan from aromatics into the wider world of flavour – and eventually whisky. Though he has stayed in academia, currently doing a PhD in flavour chemistry at Nottingham University, he says: “I read way outside my subject – anything that has an odour, good or bad, I’m interested in.”


Two seasons as a tour guide at Glenkinchie, followed by other distillery visits and numerous books, taught him about Scotch. “I’ve done loads of reading about what the main flavour compounds are in whisky, and none of them smell like whisky to me,” he says. This was the inspiration for a memorable tasting he put on for the SMWS in April with his friend and Society ambassador, Logan Shaw.

First though, Aidan explains the difference between flavour and aroma. “Flavour is an umbrella term. It encapsulates taste, texture, mouthfeel and even the way things sound, like the ‘crunch’ in certain foods,” he says. “But it’s thought the biggest contributor to flavour is aroma, which splits into two different categories – orthonasal and retronasal.”

ABOVE: Aidan Kirkwood puts his nose to the test

The former is what you sniff and the latter covers all the aromas of the food or drink in your mouth, which is why we confuse taste with smell. “The process of chewing and swallowing causes a pump of air from the back of the throat into the nose,” he says. “So, we’ve been kind of built to experience flavour.”

For our cave-dwelling ancestors this allowed a last chance to spit out that piece of putrid mammoth meat that naturally carried no ‘best before’ date. Whereas dogs, apparently, cannot do retronasal, which presumably explains why they will happily eat anything, however revolting.

At the SMWS tasting, he introduced people to beta-damascenone, which is “a major flavour compound in whisky which I believe is formed during fermentation and also from wine and sherry casks,” he says. “To me, it’s jammy, with this cooked apple note and is a little bit smoky, and our nose can detect it at much lower levels than an instrument can. I told everyone at the tasting to think about it, and think of sherry-matured whiskies.”

The widest reaction came from the sulphur compound – dimethyl disulfide. “It’s in whisky and basically anything fermented,” says Aidan. “Some people loved it, and some were disgusted by it, as it’s like garlic on steroids.” But like all the compounds he let people sniff, it seems everyone struggled to associate them with whisky.


It seems we are not very adept at deconstructing aromas in isolation, and he mentions the experiment where people are given isobutyric acid to smell and shown a picture of Parmesan cheese. Everyone agrees.

“Then the second slide is a pile of vomit and they’re completely revolted by the same compound,” he says. “So, a lot of it is context.”

While ‘butyric’ or ‘baby sick’ occasionally feature in tasting notes, you will never find them on a back label or in a press release – the very idea would make a brand-owner shudder. Whiskies must be ‘floral’ and ooze ‘heather honey’ if we are talking Speyside, be ‘crisp and salty’ if maritime, and be ‘drenched in pungent peat smoke’ if they hail from Islay. To challenge that is to challenge a sacred truth of whisky marketing.

But while such descriptors may be clichéd, they feel more reassuring than the actual flavour compounds, which can sound very weird indeed. “Trans trans-2 4-decadienal is just a really long, stupid name,” says Aidan. “It’s like chicken cup-a-soup, it’s fatty and almost reminiscent of cucumber. It’s so obvious to me in Clynelish.”

Theoretically you could construct a test-tube whisky in a lab by knowing the flavour compounds involved, though whether anyone would be taken in by it is another matter. “It would be very difficult to make it balanced. Nature is very hard to mimic,” he says, and it seems we are sensitive to noticing if something is not quite right, even if we are unable to put our nose to it.

However, he goes on to say: “We’re not tuned to try and tell what the individual notes are in a flavour, and there’s actually research to suggest that even an expert cannot distinguish between components when more than five of them are used. And with whisky there are at least 45 compounds that are important.”


In a sense you could say that a whisky is better than the sum of its parts, for it is the overall balance and how the flavour compounds mesh together that matters most.

At the same time, we should be sceptical of any whisky guru who can spew forth a barrowload of exotic fruits, having extracted their nose from a dram.

“I am not convinced by a lot of notes in whisky,” says Aidan. “To the average whisky drinker, they will likely not pick out these notes as they are so abstract, chemically, compared to the actual fruit. Then again, you would have a hard job being able to tell analytically if a whisky was fruitier than the other, because flavour synergy is complicated and enigmatic.”

And of course, taste is purely subjective. “If I say ‘it tastes like this’, it’s my childhood and everything I’ve been exposed to,” says Aidan, who points to the durian fruit from Southeast Asia.

“It is really full of sulphur compounds and for me it smells like Monster Munch pickled onion. In Thailand they just say ‘it smells like a durian’.” Suffice to say the ‘king of fruits’ divides opinions – raw sewage to some, an aphrodisiac to others.

For all his work in the lab, studying for his PhD, Aidan insists: “I don’t think of the chemicals when I sit down to enjoy a glass of whisky.” To say something ‘tastes of chemicals’ is never a compliment, and the fact they are not mentioned is a blessing.

As he says: “It would probably scare people off.”