Having looked at the components of whisky over recent weeks, Dominic turns to the production process. And because wood has been featured recently, he starts at the end of the process – with maturation
A few years back I attended a tasting of three single cask Bowmores from the ’60s. Each had been filled in the same week some 40 years previously, two on the same day. But each was from a different cask type: one Oloroso sherry, one Pedro Ximenez, one bourbon. and although the Bowmore DNA was in each, they varied dramatically, demonstrating just how important the cask is in the making of whisky.
Some claim that up to three quarters of the flavour of malt comes from the maturation process, and unless caramel is added, so does all of the colour.
But what’s even more remarkable is the fact that if all three had been bourbon barrels and had been filled with the same spirit batch on the same day and matured next to each other for 40 years, they would still have been different to each other. They would have had different flavours and marginally different alcoholic strengths, and they would have matured at different rates.
What’s more, while much these days is known about the maturation process, a great deal isn’t. This is the magic – or miracle – of malt. Science is doing its best but it hasn’t got there yet. Let’s hope it never does.
So what do we know?
First, that malt spirit needs to be matured for no less than three years in a cask, and in Scotland that cask has to be made of oak. And because the spirit is delicate it cannot hold of the spicy tannins of new oak for three years, so it needs to be put in as cask seasoned with something else – normally sherry or bourbon.
In the cask the spirit circulates and expands and contrasts slightly with the changing of seasons and temperatures. And in the cask the liquid undergoes four processes:
Firstly, the spirit is forced in to the wood, picking up flavour and colour. Secondly, during this process the wood also moves some flavours, and in particular some negative ones such as sulphur. Thirdly compounds in the wood react chemically with the spirit to produce the array of flavours we associate with malt whisky.
And finally, we know that spirit escapes faster than water in maturation – at least it does in Scotland – because over the course of several years the strength of the spirit is reduced. But the cask does not collapse, indicating that oxygen enters the cask – and thus oxidisation takes place.
Once whisky has been made after three years, it’s up to the distiller to decide how long he wants to keep the whisky maturing, but he has two constraints: one, the strength of the liquid cannot be allowed to fall below 40% ABV; and two, the tannins and spices of there wood contribute to flavour but there will come a time when it will become noticeable, then dominant and finally overwhelming. The positive flavours imparted from the cask will peak, too, so the distiller must choose carefully when the optimum flavours and the oak are best serving the final flavour. And with every cask that decision is different.
That’s a tough ask with just one cask, but what if you are storing 100,000 or even a million?
* Next week we’ll look at maturation lengths and what effects them