Shell and tube condensers originated in the late 19th century, but have only been used widely since the 1960s, replacing the original type of condenser, known as a worm (a coiled copper pipe in a tub of cold running water).
“Of the new distilleries we build, 95 per cent choose shell and tube condensers. They are more energy efficient and take up less space than a traditional worm tub,” says Richard Forsyth, chairman of Forsyths, which offers bespoke, comprehensive services.
Pragmatically named, shell and tube condensers have a copper shell (jacket), typically around 0.5-1 metre in diameter and 3 metres long.
“A shell is filled with around 250 copper tubes that have a diameter of 25mms. These are held in place by brass tube plates at the top and bottom of the shell, with around 10-12mm space between the pipes and 15-20mm space between the tubes and shell,” adds Forsyth.
During distillation vapours proceed along the lyne arm (lye pipe) to a ‘vapour chamber’ at the top of the condenser. Vapours expand into this larger, circular area, then pass through a perforated ‘strike plate,’ resembling a curved shield. Perforations ensure vapours are evenly diffused when reaching the tubes beyond. Cold water enters the tubes at the base and discharges from the top. Vapours meeting the cold tubes begin to condense on the surface. The resulting liquid travels along the tubes to the base and drains into a separate vessel. However, condensation doesn’t occur within neatly delineated sections.
“At the top of the condenser it’s 100 per cent vapours, and in the middle it’s about 50/50 vapours and liquid, with vapours also present for about three quarters of the tube length, after which it’s all liquid. Meanwhile, condensation begins near the top of the tubes and continues to take place further down,” says Ewen Fraser, engineering manager at Chivas Brothers.
The colder the water entering the condenser, the greater the rate of condensation, meaning a shorter ‘vapour phase’ and longer ‘liquid phase.’ Each phase entails interaction with copper, though the degree varies.
“When vapours condense into liquid a huge amount of energy goes into this change, and it’s when the greatest interaction with copper occurs, which means the greatest reduction in the level of sulphur compounds,” says Stuart Watts, distilleries strategic development director for William Grant.
Sulphur compounds (formed during fermentation) include meaty, vegetal, sweaty notes that mask subtler characteristics such as esters (fruitiness) and sweetness. Consequently, subtler notes are revealed by lowering the level of sulphur compounds (though a certain level can also add complexity).
Some distilleries have a water source that provides water at varying temperatures during the year. There are various options to mitigate this and promote consistency.
“Cooling water enters the condenser at the ambient temperature, usually 5-15 degrees centigrade, and when the temperature of the water is warmer we compensate for this by increasing the flow rate of water into the condenser,” says Fraser.
Dalmore has a way of dealing with water at 4-5 degrees centigrade in winter and 18 degrees in summer. “We pass the water through a chiller in the summer, which means water going in to the condenser is around 8-9 degrees centigrade, and the difference between this and the winter temperature is negligible,” says Stuart Robertson, Dalmore’s distillery manager.
Balblair’s water source, 4-5 degrees centigrade in winter and 12 or even 15-18 degrees centigrade in summer, is brought to a ‘standard’ temperature.
“We add enough hot water to raise the temperature to around 20-25 degrees centigrade. The hot water we add has discharged from the top of the condenser, at around 80 degrees centigrade,” says Derek Sinclair, distilleries general manager at Inver House Distillers.
Another comparison is a condenser’s role during the first and second distillation. The function is the same, but the dynamic changes.
“During the first distillation the goal is to remove as much alcohol as possible from the wash; in the second distillation the aim is creating a particular flavour profile,” says Robertson. Pierrick Guillaume, Caol Ila’s distillery manager, adds, “The wash condenser is the workhorse and the spirit condenser is the chef d’orchestre.”