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
Shell and tube
Most widely used, coolant passes up condenser through narrow pipes before flowing out top, pipes enclosed in container (shell), vapours enter shell & cooled by contact with cold water pipes
Advantages of shell and tube
More energy efficient, less space, cooling pipes have larger surface area, made from copper so remove more sulfur compounds, results in lighter & cleaner spirit
Scotland
1 distillery equipped with 2 shell
& tube condensers, 1 copper & 1 stainless, can vary styles by switching between them (when switched off)
Worm tub
2 parts: large vat of cold water (tub) & single coiled tube (worm) placed inside vat of water, vapours pass into worm & slowly condense, liquid flows out pipe at bottom
Other condensers
Rrustic stills (Mezcal, Korea, China & Japan), variation of dephlegmator, placed at top of still & not separate from it, have 1 part- bowl of cold water- constantly flowing & refreshed, bowl sits on top
Process of rustic still condensers
Hot vapours rise & condense on underside of bowl, some liquid drops back down, some flows along underside of bowl to base & drips into small vessel that feeds a tube, it directs it out & is collected
Multiple batch distillation
Most distill 2x, some 3x, a handful once
Scottish double pot still distillation targets
1- raise alcohol from 10% to 40% abv
2- get close to collecting ethanol from original liquid
1st distillation
1st liquid off is 55-60% abv depending on still, when 40% abv continue because ethanol still in original liquid
% abv starts to drop in 1st distillation
Continue until abv coming off is 1%, hardly any ethanol left in still, collected liquid about 15% abv, drops because higher prop of ethanol becoming vapour, continues & ethanol in vapours drops too, to collect enough ethanol a large amount of water has to be collected
Principal aim of 1st distillation
To remove some water & group-4 fractions
2 outputs of 1st distillation
1- low wines- about 25% abv
2- liquid waste- remains with tiny amount of ethanol, some less volatile fractions & all of non-volatile fractions, some discard, some larger distilleries process as syrup for cattle feed
2nd distillation
Low wines, heads & tails from previous 2nd distillation placed in still, between 25-30% abv, still is turned on
Outputs from the condenser
Liquid flowing off 1st has high conc of group-1 fractions (most volatile), also has group-3 fractions (left as residue at end of previous 2nd distillation)
Heads
Liquid collected for 15-20 minutes, has high amounts of unwelcome fractions, flow redirected into 2nd container, ‘cut’
Hearts
Collected a few hours depending on size of still & how it’s being operated, high conc of group-2 fractions, another cut made & redirected to container containing heads
Tails
High conc of group-3 fractions (least volatile), collection continues for several hours until abv is 1%
Temperature in the still
Gradually increases d/t changing composition, as conc of ethanol & volatile congeners falls, temp rises to 100 C (212 F) (boiling point of water), contributes to rise in conc of group-3 fractions
Heads & tails
High levels of group-1 & 3 fractions, also contains ethanol & desirable congeners so recycled back with next batch
Heart
Becomes spirit sold, straight off still is 70% abv
Liquid waste
Water & group-4 fractions
Using cuts to shape style
Flow reaches highest conc in order from most volatile to least, vapours at any time are mix, determine what to include & what to exclude
Inclusions
Group-2 & what wanted to select & conc (narrow cuts), small amounts of group-1 & 3 fractions can give extra dimension (wider cuts)
Group-1 fractions
Can give attractive aromatic lift
Group-3 fractions
Can add palate richness & extra complexity
Separating fractions
Limit, level of separation improved by raising level of reflux, run hotter & reflux reduced- more group-3 fractions will come out
Temperature management
1- high heat with small difference between top & bottom, quick distillation & high flow rate, peaks of conc compressed, harder to separate group-1 & 3 fractions
2- lower heat, wider temp difference, longer distillation, slower flow gives more separated peaks, easier to exclude group-1 & 3 fractions
Exclusions
Group-4 fractions excluded (never leave still), separate unpleasant smelling fractions from heart, heads & tails separated & recycled (contain ethanol & group-2 fractions), gin distillers sell them off
Advantages of pot stills
Reliable, centuries long processes, difficult to reproduce if changes made (ex. stainless- durable & easy to clean but copper has vital role)
3 challenges of pot stills
Operating costs, inability to make highly rectified spirits, prevent build up of group-3 fractions during extended distillation
Operating costs
Historically large workforce, many repetitive tasks, time consuming, can be automated, now Scotland distilleries have handful of workers
Rectification
Triple distillation can reach 80% abv, not possible to go higher, direction of travel is one-way, vapours move from boiling liquid to condenser, amount of reflux & liquid returned to pot are limited, have to include other fractions to conc, with tighter cuts & discarding more this issue remains
Eliminating group-3 fractions
Recycling heads & tails- get a build up of group-3 fractions, fewer group-1 fractions so not an issue
