Ian Wisniewski asks that all-important question: does the way a still is heated affect the final product?
The focus tends to fall on the influence that a still’s shape, size and accessories such as boil bowls or purifiers have on the character of the new make spirit. But the rate of distillation is also crucial, and that depends on controlling the heat applied to the still, using either the indirect method (steam-heated coils within the pot) or direct-firing (burning coal or gas to heat the base of the pot).While indirect heating is considered the easiest to control, and used by the majority of distilleries, that’s only one consideration in a broader debate. Indirect heating applies a gentler, more uniform build-up of heat in the wash compared to direct-firing. Additionally, direct-firing potentially creates a more variable range of temperature on different parts of the pot’s surface, which in turn can prompt different flavour effects.Any changes to the heating method can also alter the temperature profile and so the distillation rate, which in turn affects the character of the new make spirit. Hence some distilleries agonise over changes to their heating methods, while others retain direct-firing.Glendronach is a rarity in using coal, the most traditional method of heating stills. The type of coal, ‘washed singles,’ is sourced from central Scotland and considered the most efficient for this purpose. During a distillation run, coal hoppers feed pieces of coal, around 3cm squared, into a fire box beneath the still.The options for controlling the fire are either to increase or decrease the rate at which coal is fed into the furnace. Opening the furnace doors is also effective, allowing more air in to cool the fire. However, as Tom Lee, Glendronach’s distillery manager, explains:“Coal isn’t 100 per cent consistent, and you can get minor differences in coal from load to load. So you do it by eye and experience. It’s a skilled job.”Even before reaching the furnace, coal entails physical effort to move it around. Subsequently, ash needs to be cleaned out from the firebox, while how and where it is disposed of requires approval from The Scottish Environmental Protection Agency.Gas is another option for direct-firing, and being able to adjust the heat instantaneously by opening or closing a gas burner is obviously far simpler than managing coal. Gas is also a more efficient fuel than coal, although gas prices fluctuate where coal prices are more stable. Glenfiddich introduced gas to No. 2 stillhouse in the early 1990s, while No. 1 stillhouse continued running on coal.“There was a lot of trialling first, and we did a lot of spirit analysis to determine that the same spirit was being produced. The spirit from No. 2 stillhouse was exactly the same as from No. 1, and we are now phasing in gas heating and no longer using coal,” says Ian Millar, Glenfiddich’s distillery manager.“Gas burners are set up to ensure the same flame profile as we got from coal, to achieve the same temperature over the same area.”A consequence of using direct-firing is the risk of solids within the wash burning onto the still, which can caramelise and affect the new make spirit. This is prevented by installing rummagers. Essentially lengths of copper ‘chain mail’ around 30cm wide, they drag across the wash still base, driven by motorised arms, removing solids which have lodged there.As the rummager remains submerged beneath the level of the wash, a higher level of copper is inevitably presented to it.“More copper carries over into the low wines, but not into the new make spirit as there is no rummager in the spirit still. This leaves a higher copper content in the spent lees and pot ale,” says Tom Lee.Another consideration is the effect of the rummager on the liquid, rather than solid, element of the wash.“Churning the wash also has some effect during distillation, but exactly what is difficult to quantify. Having a rummager is a bit like stirring a pot while it’s cooking,” adds Tom Lee.He also sees a difference between the character of new make spirit depending on the heating methods."Direct fire gives certain components that steam doesn’t. Blenders love direct fired whisky, it produces things they like.”John Grant, chairman of Glenfarclas, certainly agrees with this. While committed to using direct-firing (gas burners), steam heating was given a chance at Glenfarclas.“We did an experiment in 1980, with steam coils in one of our spirit stills. It certainly proved more economical than the direct-firing, however we did not continue for more than a week,” says John.And the result of the experiment?“Even using the same cut-off points we made a totally different spirit. All the character had gone, and it was very bland. The body and guts had disappeared and it was not something we would be proud of. All of the production was used for blending as it did not have the character of Glenfarclas,” he explains.But is it inevitable that any changes to the heating method will affect consistency?“If you just install coils, then the whisky will be different, but there are lots of things you can do to emulate the effect of direct firing, and you’ve got to spend time, money and dedication to achieve this,” says Robert Hicks of Allied Distillers.“After nine months of experimenting with steam coils at Ardmore, it was a case of getting a balance between the hot spots, gentle heat build-up and reflux, and now Ardmore’s character and style is the same.”As many distilleries began switching to steam-heating during the late 1950s to early 1960s, it is typically considered a recent innovation. However, when Scapa opened in 1885, steam-heated stills were part of the original ‘tech-spec.’ Glemorangie’s stills, best known as the industry’s tallest, have also been steam-heated since 1888.It’s a straightforward concept. Steam is conducted along tubular copper or stainless steel coils, placed within the stills in various configurations. A set of four to five coils fixed around 30cm from the inner surface of the pot is typical, though coils can also be placed more centrally, or tailored to the shape of the still. Some configurations have larger top and bottom coils, nick-named ‘beehives,’ with another option being coils that extend or zig-zag across the pot.“It doesn’t matter what configuration you have, it’s the surface area that matters, and it’s all about using a certain amount of steam to boil off a certain amount of liquid in a certain amount of time,” says Richard Forsyth, of bespoke still-maker Forsyths.Be the coils copper or stainless steel, a semi-polished surface also helps reduce the level of solids burning onto them.“Most of the industry uses stainless steel; it’s easier to clean and the coils last around 20 years in a wash still, and 15 to 20 years in a spirit still, compared to copper coils at about 15 years in a wash still and seven to eight years in a spirit still. Wash doesn’t attack copper like the stronger low wines and feints,” adds Richard Forsyth.An alternative to coils are stainless steel cylinders known as ‘kettles’ (or ‘pans’ or ‘percolators’), which are more usual in a wash still. About 30 to 60 cm long, and 45cm wide, four to five kettles are typically used per still, with small pipes branching off a central coil conveying steam to each kettle.“Generally, kettles are slightly more expensive than coils but offer a longer life, good boiling action and are easier to clean. A stainless steel kettle lasts in excess of 20 years in both types of still,” says Richard.Apart from the effect on the new make spirit, the heating method also has a significant effect on the pot of the still. Apot heated by direct-firing needs to be about 12 to 16mm thick, compared to a steam-heated pot at around 6mm. Direct-firing also reduces a pot’s life expectancy to 15 to 20 years for a wash still, and eight to ten years for a spirit still, compared to 20 to 25 years and 12 to 15 years respectively for steamheated pots, explains Richard Forsyth.
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