Sulphur and the tale of two whiskies

It all began at Dramfest back in March last year at the Signatory stand with a beastly bottle of Deanston (and I mean beastly in a good way). You remember the one - an abv as hot as hell and fumes of brimstone to match. I loved it, and wasn’t the only one, and I guess that’s down to the fact that, at the end of the day, some of us really do love a dash of sulphur in our whisky.

Many distillers go to great lengths to remove the stuff - the copper in their stills being the first line of attack, and there are many techniques and approaches employed that enhance this play. Taller stills that increase the conversation between malt and copper, triple distillation, the shape of the still and other techniques to increase reflux, such as a lyne arm that angles upwards. That said, there are also those who strive to create a heavier style of malt and, in this case, we often find a hint or more of sulphur. Mortlach is an interesting example. Here partial triple distillation is offset by a small, squat spirit still known as Wee Witchie and worm tubs for condensers. The result is a famously meaty spirit and has led to its nickname - the Beast of Dufftown.

But to say that sulphur’s presence in whisky is one that is easily understood would be untrue - it really does seem to be one of the main contributors to whisky's mercurial and often unpredictable nature.

Which brings us back to our splendidly eggy Deanston at Dramfest.

A sulphurous Deanston is certainly not unheard of and, in fact, I have come to expect it following several previous encounters (Deanston, One Giant Leap,10yo, WB1003 61.6 %, Deanston Signatory 2006 11yo 64.4%). And so when I was lucky enough to stumble across another Signatory Deanston, this one from a sister cask to that which was available at Dramfest, it was with great gusto that I lowered my proboscis into the glass with the anticipation of another visit to Deanston upon Rotorua. But this one was clean, clean as a whistle!

Where was the sulphur? Where had it gone? Or was the right question - why was it present in the other bottle? Some detective work was called for.

Below are the stats for the two bottles, the first being the sulphurous one.

Deanston Signatory Vintage (SV) 11 years old 67.8% Vol.
Distilled 13.08.2008, Bottled 17.09.2019, 1st Fill Sherry Butt #900072
Number of bottles: 605

Deanston Signatory Vintage (SV) 10 years old 67.7% Vol.
Distilled 13.08.2008, Bottled 12.02.2019, 1st Fill Sherry Butt, #900074
Number of bottles: 597

As you can see, they really are sisters in many respects. The new make presumably would have been from the same run, having been distilled on the same day, the cask numbers are very close together and even the number of bottles from each cask is almost identical. The only real differences are 7 months further ageing and, of course, the cask itself, after all, no two casks can be exactly the same despite both being first fill sherry butts.

There are two possibilities with regards to the sulphur. It was either in the new make and was somehow absorbed or released in the clean cask or was added by the cask somehow in the case of the Dramfest bottle.

It seems unlikely that an extra seven months in cask would have created the sulphur, although sulphur does tend to be linked to reduction, and so a tighter cask, perhaps with less oxidation, could have possibly triggered something. There were more bottles drawn from the sulphurous cask, which would go along with the notion of a tighter cask and less evaporation - but the difference in bottling number is so small that you'd be hard pushed to argue this as a plausible cause.

Could the sulphur be due to a failed attempt at cleaning the cask? This is a theory that Jim Murray has almost exclusively blamed for the surge of sulphur seen in whisky today. Shipping sherry in anything other than glass was banned in the early 80s and his theory is that empty casks, destined for Scotland, languish on the docks and then require stringent cleaning. This was, and is still is, often done using a sulphur candle, which hangs from a line through the bung hole. Candles have certainly been known to fall into the cask or simply produce a level of sulphur that is too much. This is certainly a possible cause, but with sulphur seemingly being quite often present in single cask Deanstons - surely this can't always be down to poorly managed sulphur cleaning?

There is also the theory that sherry casks can inherently add sulphur and not as a direct result of being poorly cleaned. I have heard this from more than one source, and especially with regard to PX casks. This could be something specific to tighter grained European oak, or the residual sherry itself, after all, sulphur is a byproduct of fermentation. Further to this, sulphur is seldom seen in ex-bourbon cask aged whiskies.

Rather frustratingly though for our whisky detective work, the exact opposite opinion seems to exist too. That is that ageing in a decent sherry cask can result in the integration or extraction of Sulphur- essentially through oxidation or evaporation.

So where does this leave us? Well, unfortunately, the cask as the source of the sulphur seems nigh on impossible to prove one way or the other and this brings us back to the new make.

Dave broom describes the Deanston new make as heavy with snuffed candle aromas and this would seemingly correlate well with sulphur being an inherent part of the distillery style (and presumably tracing back to the fermentation stage).

It’s a fair summation that a distiller wishing to make a meatier, heavier malt would not want this to be the predominant overpowering factor, but more a complexing note, and time in cask should be a way of achieving this when starting with a new make that leans to the sulphurous side. But, perhaps time doesn't always do the trick, and maybe this is simply what we are seeing in these indy single cask bottlings. These are whiskies at one extreme of the spectrum where the sulphur residue of a heavy-styled new make has simply not integrated into the whisky, nor been filtered out by the oak.

With official bottlings and distillery releases, these casks would typically become an ingredient in a broader based blend or vatting - edges will be rounded out and the extremes removed. But when bottling is straight from the cask, we see the malt in its true and unadulterated splendor - whatever form this may take.

Of course, whether one finds this a thing of beauty or an abomination is simply a matter of subjectivity.