On a recent trip to that spiritual home of whisky, Scotland, I acquired a (-nother) whisky book, penned by a very well known whisky personality of high repute. Sifting through this guide book, a couple of statements attracted my ire – one being that ”it is claimed that steady maturation is upset by wide temperature fluctuations” and hence that an even temperature over the year is preferable.
Now, this issue could and would be subject to differences of opinion. But some objective facts can also be stated. Such as that variations in temperature will inevitably – albeit on a very small scale – lead to materials such as oak wood (in the casks), the pores within the oak and also the whisky itself (density changes with temperature) will change their exact physical features as well as their chemical properties and behaviour (higher temperatures typically offering a higher rate of chemical reactions). If a temperature is steady, a more narrow set of environmental and chemical properties would affect the whisky as it matures. Although the steady temperature would also likely lead to a more limited loss of spirit to the ”Angels’ share”, which might please the accountants out there; however, accountants are not widely known for excellence in actually making whisky.
Variations in temperature can be regarded as the engine that drives maturation forward to full maturity. This, I would claim, is due to the aforementioned changes in density and expansion/shrinking as an effect of temperature changes. Warm temperature means higher chemical activity, widening pores in the oak, slightly expanding casks and certainly expanding whisky due to changes in density. Cold temperatures mean the opposite. In effect, whisky is sucked into the oak staves more readily in summer and reacts more actively with the oak; but in winter, or other cold spells, the congener-laden whisky inside the oak staves is in part pressed out into the large volume of whisky inside the cask body, where it will readily mingle with the existing whisky. Winter and spring will, discernibly at least in very young whisky, then offer a period of cold marriage where the creation of more character during the warmer period will calm down and integrate, to further a more complex and well integrated whisky. In older whisky this is less discernible, but the basic function should be the same.
At Smögen, our warehouse is not temperature controlled and – though safely locked – is basically open to the outside temperature and humidity (we’re a coastal distillery and humidity in the air is of significant importance). Temperature in the summer will normally top out at 19° C and in winter it will typically reach at least as low as -10° C at some point, really cold winters such as 2010 and 2011 even down towards -15° C. That temperature variation of around 30° C is fairly significant and will impart an effect on the whisky.
In the summer of 2018, we unusually reached temperatures of over 30° C outside already by the 10th of May – and then followed a summer where there was very little rain but week-long bouts of daytime temperatures well over said 30° C. The temperature within the warehouse topped out at just over 21° C. After that summer, the effect on the maturing casks of whisky was immediately obvious, with a real leap forward in cask-derived congeners (flavours) and also in fruity notes (esters) within the whisky. A certain nervousness in character was also present, but this was ironed out once winter had passed. Subjectively, those mere 2° C higher top temperature during the (extra long) hot summer had set a most palpable mark on the whisky. Temperature matters. And provided that harmony is allowed to re-establish itself, it is typically for the better; a steady temperature meanwhile would offer a more uniform and – it is contested – slower rate of maturation and resulting in a less complex maturity at a given age. The great asset of malt whisky from pot stills lie in its inherent complexity of character, and why would a more complex maturation process not contribute positively to that?
Next time, or at some point, my ire about different ”maturation windows” and less balanced periods during the maturation cycle of a single cask might be penned into the blog. Or not. That will be a complex and subjective, possibly even divisive, topic, or perhaps rather an anecdotal one. But having sampled a great many casks at different ages, I feel certain that I do have a soundly based understanding of that minefield as well. As a cliffhanger, suffice to say that whisky does not mature in a perfectly linear fashion…