In the last part of my travelogue I described the distillation process at Springbank Distillery. The result of the distillation is not Whisky – it is called Spirit. To become Scotch Whisky, the Spirit has to mature for at least 3 years in casks made of oak. In addition to influences coming from the used water, barley type, peat levels and pot still types, the most important contributor in adding flavours to the Whisky is the maturation in the casks. The secret behind this topic was analysed a thousand times by experts already and you can find a lot of interesting websites. For instance on Whisky.de or Malt Madness.
Cask and Wood Types
The majority of casks used in The Scotch Whisky Industry are:
- Barrels (average size of 200 litres, originated from the Bourbon Industry in America)
- Hogsheads (average size of 250 litres)
- Butts (average size of 500 litres, originally coming from the wine and sherry industry)
Oak is the best suited kind of wood because it provides a very tight container and does not deliver unpleasant flavours to the Spirit. In Europe only two kinds of oak are used. These are Quercus Robur and Quercus Sessilis. Oak used in American cooperage is called Quercus Alba.
Before the casks can be filled with Spirit they have to be prepared. In the week we’ve been working at the distillery we had to fill ex-bourbon cask. They just arrived at the distillery and after being inspected by Gavin MacLachlan (distillery manager) we had to prepare them. Each cask has to be marked with a unique number, the distillation year and the name of the distillery. At Springbank this is done by hand stenciling. What a nice job for Students of the Whisky School.
At Springbank Distillery the crystal clear Spirit is filled into the casks with an alcohol content of 63.5% (ABV). This is the usual ABV in the Scottish Whisky Industry. One reason for an uniform strength is that it eases the common practice of exchanging casks between the different blenders. That was very important in former days. Some distilleries, like Bruichladdich (70-72%), fill their casks with a higher strength.
The Spirit that comes from “The Spirit Receiver” is transferred to “The Spirit Receiver Warehouse Vat” where it is diluted with water to an alcohol strength of 63.5% ABV. The tank used at Springbank Distillery has a capacity of 23.500 litres.
At Springbank Distillery the prepared casks are filled by hand. The diluted New Make Spirit is pumped from the tank into the casks and for each cask the actual content is gauged. The number of litres is then recorded and written onto the cask.
When we where filling casks we rolled them to a dunnage warehouse afterwards. This is a really heavy work and especially getting the seal exactly to the top having the cask in its’ final position is a difficult thing.