Whisky Magazine Issue 108
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Ian Wisniewskiasks how significant is the choice of heating method when distilling?
There are two methods of heating the stills. Direct firing means burning gas or coal to create flames that heat the exterior of the pot (ie. base of the still), while indirect heating means conducting steam through tubes arranged within the pot.
Choosing either method involves practical considerations, such as differing maintenance costs, and the heating method can also influence the character of the new make spirit.
Direct firing was the traditional method, though most malt whisky distilleries in Scotland switched to indirect heating between the early 1960s and mid 1980s. This requires an oil or gas fired boiler to produce steam, which is conducted along tubular copper or stainless steel coils. A set of four or five coils fixed around 30cm from the interior surface of the pot is typical, though coils can also be tailored to the shape of the still. Another option is fitting stainless steel cylinders known as ‘kettles' (also termed ‘pans' and ‘percolators'). Again, four or five are typically used to heat a still, with small pipes branching off a central coil conveying steam to each kettle. Whichever option is used the heating elements must remain ‘submerged' below the surface of the liquid being distilled.
Steam provides the gentlest, most uniform build-up of heat, and opening or closing a valve (from the convenience of a control panel) is all that's required to adjust the flow of steam. Consequently, steam is considered easier to control, and provides a more immedi...