Sitting in an upmarket restaurant drinking single malt scotch that retails, in the USA, for $7,000 a bottle is how adventures should begin – exactly how my rancio odyssey started.In 1997 a group of writers and whisky enthusiasts were invited to taste the 40-Year-Old bottling of Bowmore that had just been released in New York. Jim McEwan, the Brand Ambassador, expertly led the tasting in his usual witty manner and informed us that the small portion of whisky sitting in front of each of us was worth between $300 and $400. We didn’t gulp.A strangely flavoured whisky, it was as if it had gone through a metamorphosis and transcended into another dimension after so long in the wood. Very intriguing, especially as one particular taste element of the spirit completely eluded categorisation by my taste buds. I could only decipher it as being an earthy, cheesy, mushroomy flavour that held hints of soy sauce On my way home that day I discussed this flavour with my friend and fellow spirits writer, Paul Pacult. What the heck was it? We were both at a loss to explain this flavour. Eventually our conversation came around to rancio. Maybe that was the answer. But how could we ever know for certain? The tasting was over and we weren’t willing to spend that much money for a whole bottle. Suddenly, Paul was inspired – “Let’s hold a tasting of the oldest malts we can get our hands on,” he suggested. And that’s exactly what we did.We managed to persuade 13 distilleries to delve into their warehouses and send us samples of the oldest stock they still deemed drinkable. What we received was made available at a grand tasting held at New York’s Rainbow Room. Paul and I believed that we had detected rancio in six of the bottlings. It was most prominent in a 1966 bottling of The Balvenie which, luckily for all whisky lovers, is now available as The Balvenie Vintage Cask 1966. But were we right? Was it really rancio?Rancio is a flavour as definite as it is elusive – I’ve heard it described in many different ways by different people and it’s one of those accents that not many people recognise until they’ve tasted it on quite a few occasions. They might say that there’s a mustiness in the spirit or a flavour reminiscent of grandmother’s attic. Some people even believe that rancio is a flavour that suggests the whisky has spent far too long in wood. Maybe it does – but then again, maybe it doesn’t.It’s been almost three years since the Rainbow Room tasting and during that time I believe I’ve tasted rancio in half a dozen commercial bottlings of single malt Scotch but it wasn’t until recently that I had a chance to add further weight to my theory.I have an ongoing e-mail correspondence with Alexandre Gabriel, a partner in the French spirits company Gabriel & Andreu, and earlier this year I wrote to ask him what he knew about this baffling flavour. For once in my life my timing was impeccable.Gabriel is one of those people who loves to dig deep into every aspect of distilled spirits – the history, the distillation process, maturation, in fact anything at all that will broaden his knowledge of the subject. At the time I wrote to him he was also hunting for the elusive rancio.He initially explained that, in his opinion, rancio could occur only in spirits that had been distilled out at low proof. This process would produce the congeners (impurities) that are, for the most part, the flavour elements in a spirit that after long ageing in wood allow it to develop the earthy tones that had started my quest. But he didn’t stop with mere opinion. Gabriel had hired scientists (Jean-Paul Vidal of the Union Nationale des Groupements de Distillateurs d’Alcool was one of the main researchers) to try to discover the chemical makeup of rancio and he shared his results with me.Unfortunately the chemical terms he used were, of course, in French. I then had to find a translator – enter Dr. H. S. Dugal, CEO of Integrated Paper Services in Wisconsin. You might wonder how somebody in the paper business got mixed up in all this but a chemist is a chemist and this one just so happened to speak French!The two liquid organic compounds that Gabriel’s scientists had pinpointed for being chiefly responsible for the flavour were both ketones known as Heptanone and Amyl Ketone. But whereas they are necessary for rancio to occur, Gabriel explained that their “association” with other molecules was needed to complete the process. Perhaps the highlight of my conversation with Dr. Dugal, who, for religious reasons, doesn’t drink, came when he asked me what rancio tasted like. I gave him my usual explanation (earthy, cheesy, mushroomy, maybe a dash of soy sauce, etcetera) and to my amazement he said: “Oh, that’s definitely heptanone.” We were definitely on to something.The next step was to discover whether these ketones were ever found in Scotch – for this I needed a couple of favours, both of which were graciously granted. William Grant & Sons sent a bottle of their 1966 vintage Balvenie to Gabriel and in turn his scientists ran it through the same tests that they’d used to analyze the brandies. Both ketones were present. Voilà! Presque voilà.It seemed to me that I should see if I could find one more scientific type to back up this theory before I went blabbing it to the world, so I approached the Scotch Whisky Research Institute in Edinburgh where research scientist John Conner was kind enough to give me an overview of the subject.Conner broke the problem down into two separate issues: firstly, can the chemical reactions that produce the aroma compounds occur during prolonged maturation? And secondly, if the compounds were formed in Scotch (as opposed to brandy) would their effect be described as rancio?“I cannot think of any reason, chemically, why the same reactions that occur during prolonged ageing of Cognac should not occur during the aging of Scotch. The fatty acids that are thought to oxidise in Cognac are also present in Scotch whisky,” explained Conner. “However, the relative amounts present will vary due to differences in the raw materials, fermentation, distillation etcetera.“Attempts by French workers to re-create rancio using only methyl ketones failed, indicating that other compounds, as yet unidentified, were important in creating rancio flavour. Without the full recipe it is impossible to say how the variations in fatty acids between whisky and brandy affect rancio reactions and whether the result is the creation of rancio in Scotch every time or only under certain conditions (wood type, warehouse environments, etcetera).”That made sense to me – Gabriel had already said that it wasn’t just the ketones that were responsible for the flavour, but more their reaction with “other molecules” within the spirit. Conner also noted that the “odour potencies” of both heptanone and amyl ketone are “unremarkable” so other forces, unknown to us at present, must be at work. But Conner’s answer didn’t deter me – we had started this journey on our tongues and as far as I’m concerned the opinion of our taste buds combined with some fairly stunning chemical evidence is enough to convince me that Pacult and I had been right when we conducted the Rainbow Room tasting. The second question, though, raises some big issues.Basically Conner is asking this question: If there’s rancio in Scotch, should we still call it rancio? I think that that’s fairly simple to answer, too. We detect, say, peaches in both Scotch and cognac but we don’t look for different terms to describe them just because they are in different spirits. Rancio is rancio no matter where it’s found. But although rancio is eminently desirable in cognac, does that make it something that the Scotch fancier wants to taste in his or her dram? “It may be regarded as a distinctive character of old brandies and therefore out of place in a well-matured Scotch,” noted Conner. And there’s the rub.Do you want rancio in your Scotch? Is it a good thing, or is it a bad thing? Conner said that it’s possible that “woodinesss” is a term that might be applied to rancio when found in Scotch and we’ve all been taught that woodiness is undesirable in our malts.I happen to love the flavor of rancio whether its in Scotch, cognac, armagnac or calvados. I think that it’s possible that if you search deep into your soul and re-taste a whisky that’s been described as “too woody” or “over-aged” you might just find that delectable complex earthy flavour that should be savoured, not shunned. I recommend that you find an upmarket restaurant and order a very old malt – a taste adventure awaits you.