6- Pot Stills Flashcards
Common features
4 elements: heat source, pot where liquid to be distilled placed, condenser, structures (tubing) that link pot & condenser
Direct heat
Original method, wood or coal, rustic pot stills for Mezcal, controlling heat accurately requires skill & monitoring, difficult to maintain even heat across base, creates hot spots & can scorch any solids giving off flavours, well-managed heat spots can increase Maillard reactions & contribute flavour
Gas burners
Larger scale, legally required for Cognac, some in Scotland for malt whisky, easier to control, burners placed for even heating, scorching solids still an issue- use mechanical scrapers so that solids don’t settle
Indirect steam heating
Steam most widely used, cost benefits, easier to control, steam created in boiler, need water & fuel, steam piped into still & never comes in contact with liquid, heat exchange- keeps liquid boiling, as liquid heated steam cools down & condenses so fresh steam constantly introduced, flow rate & temp controlled & quickly adjusted
Coils
Steam piped through coiled pipe submerged in liquid, not as common because still issues with scorching
Jackets
Most widely used, mounted on outside of pot & provides very even heat over largest surface area, very efficient, lack of hot spots- low chance of scorching, still use mechanical stirrers
Jacket variation
Replace steam with boiling water, water directly heated, used by smaller distilleries (steam boiler more $$), not as responsive, water at lower temp so less energy supplied
External heat exchangers
Liquid pumped out & recirculated back, ensures large surface area for heating & continual, rapid movement reduces risk of scorching
Steam injection
Only option for solid-state fermentation (baijiu), also for liquids with very high solid content (pomace brandies, Grappa), stills have inlet for steam at base, steam introduced at high pressure & forced through material, heat causes volatile fractions to evaporate & pass out top, requires direct contact so quality of steam can impact
Managing reflux
Low levels create fuller & richer spirit, amount of reflux in pot still limited
Still height
Easiest way to manage reflux, tall stills have cooler still heads & promote more reflux
Lyne arm
- points downward- no further reflux can take place, even if vapours condense in tube they still flow into condenser
- angled upwards- any condesation can flow back into still & reflux continues until vapours enter condenser
Intensity of the boil
Changing heat input is how most control consistency of temp gradient
Plates
Rare in traditional pot stills, modern hybrids- purifiers in 2 Scottish distilleries, add reflux in form of vertically-oriented plates on lyne arm
Dephlegmators
Rare in traditional stills, common in hybrids
Internal cleaning systems
Modern stills have pipes with sprinkler heads or ‘spray balls’, copper gets covered in residue & stops being available for sulfur management, dirty stills can affect quality
Pressure management
Pressure changes can damage still & in extreme cases explode, when filled displaces air so hatch or valve needs to be open
Pressure during operation
Pressure inside higher so strong enough to withstand, needs safety valve, challenging during 1st distillation when CO2 released (dissolved in fermented liquid)
Pressure when turned off
Gases cool & contract so pressure drops creating partial vacuum, valve open to prevent being crushed, emergency anti-collapse valve
Computer controlled
Modern stills designed to prevent unsafe conditions
Condensers
Heat exchangers that rely on coolant (cold water), most common- shell & tube, worm tub, water constantly introduced at base & taken from top, water leaving is warm & is cooled, vapours enter at top (hottest part) & gradually cooled while passing through coldest part at bottom
