FLAVOUR FOCUS
Distillation (part one)
The stillhouse is the beating heart of every distillery, the glamorous showpiece every visitor wants to see. This is what all the milling, mashing and fermenting has been leading up to, as Gavin D Smith explains
PHOTOS: PETER SANDGROUND / MIKE WILKINSON
Stills are made of copper for a number of very good reasons, though the earliest would have been created from glass or ceramic material. Ultimately, copper became the material of choice for still construction because it is malleable and relatively easy to work with, an excellent conductor of heat and resistant to corrosion.
Copper may be seen as a ‘silent contributor’ to spirit quality, as within the still it allows complex chemical reactions to take place, removing volatile sulphur compounds and aiding the formation of esters, which contribute to the fruity character of spirit.
In a malt whisky distillery, there are usually two consecutive periods of distillation, the first in the wash still and the second in the spirit still. The spirit still is usually smaller, as it has less bulk of liquid to accommodate. Triple distillation, as practised at Auchentoshan and the recently reopened Rosebank distillery in Falkirk, involves a third intermediate still, which fits between the wash and spirit stills.
The shape and size of the pot still, along with the manner in which it is run, contributes significantly to the character of spirit produced, thanks to the key role played by the copper from which the still is fabricated, and these variables will be explored next month when focusing on spirit still distillation.
Essentially, the pot still functions as a large copper kettle, and is effective because alcohol boils at a lower temperature than water. The initial distillation in the wash still serves to separate yeast, water and the fermented wort residue known as ‘pot ale’ from alcohol, but the importance of its role is often underestimated. If the correct flavour potential is not created in the wash still, then the desired character will not appear in the new-make spirit. The residue yeast is still present in the wash still, along with some residual sugars and proteins, so a significant range of compounds are reacting together.
ABOVE: stills of various shapes and sizes at Mortlach distillery in Speyside
“Since reverting to direct-firing, there is a distinct difference in the new-make spirit, which has more caramel notes and more body”
Most pot stills are heated by steam coils or radiators, though some distilleries use ‘direct-firing’, with a flame usually fuelled by gas. In 2021, Glen Garioch distillery in Aberdeenshire took what could have been seen as a ‘backwards’ step when its steam-heated wash still was converted to direct-firing by way of gas.
Kwanele Mdluli, Glen Garioch’s distillery manager at the time of the conversion, explained the rationale behind this move. “It’s all about spirit quality. Since reverting to direct-firing, there is a distinct difference in the new-make spirit, which has more caramel notes and more body.
“The temperature with steam was 130-40 °C but with direct-firing the temperature gets up to over 1,000 °C. You’re putting lots more heat in. Increasing the temperature even by just 10 degrees doubles the rate of chemical reactions, leading to more flavour compounds being created.”
It has been estimated that heating methods account for some 20 to 30 per cent of the character of spirit produced during the wash distillation, with the size and shape of the still in question being responsible for a much higher percentage.
Whether directly or indirectly heated, when the temperature of the wash in the wash still reaches around 78°C the alcohol begins to boil, and many wash stills are characterised by the presence of two ‘sight glasses’, which allow the stillman to judge the extent of the boil, keeping the frothing liquid between the two sight glasses. However, computerisation of processes in modern distilleries makes such visual aids less important than was formerly the case.
ABOVE: Glen Garioch distillery say they find more caramel notes and body in their new-make since reverting to gas direct-firing
PICTURED: SMWS head of whisky creation Euan Campbell at Mortlach distillery
As the wash heats, it begins to give off vapours, which condense against the copper of the still, with the vapour rising to the top of the still. It then passes through the copper lyne arm that connects the still to the condenser. There, the vapours are cooled back into liquid form, known as low wines, originally termed ‘low grade wines’ as they are effectively halfway between water and spirit.
The low wines have a strength of 20-30% abv, and are collected in the low wines and feints receiver. In total, the wash still distillation lasts for between four and seven hours and runs until the strength reaches around 1% abv.
The method of condensation involves a copper-related variable in addition to the influence of copper during distillation, with most distilleries now employing ‘shell and tube’ condensers. First introduced during the early 1960s, these comprise a shell, fitted with copper tubes, which are filled with cold water, causing the spirit to condense as it passes through the apparatus.
However, some distilleries such as Dalwhinnie, Glenkinchie, Oban, Pulteney and Talisker continue the old practice of condensing spirit by way of a ‘worm tub’, which consists of a spiralling, tapering copper ‘worm’ located in an external wooden or steel tank filled with cold water. The result of using a worm tub is that the spirit condenses more quickly and has less copper contact than in a shell and tube condenser, leading to a heavier, more ‘meaty’ character.
Once wash distillation is complete, the nutrient-rich pot ale is removed from the still and is often processed into cattle feed, while the low wines are transferred from the low wines and feints receiver into the spirit still, where the second distillation takes place.
PICTURED: the Frilli Italian stills at Raasay distillery