7- Column & Hybrid Stills Flashcards
Heat sources
Some directly heated (Armagnac), most use steam
Indirect steam
External heat exchangers- reboilers most common
Steam injection
Large operations, adds water-has to be removed, Maillard reactions minimized (advantage for light or neutral aromas)
Managing reflux
Internal structures designed to manage reflux, most fitted with rectification plates, some use packed columns
Advantage over pot stills
Can make spirit highly rectified as 96% abv, can run continuously
Rectification plates
2 features:
1- force gas & liquid to interact more than pot stills, unlike pot stills can control reflux tightly, vapours rising up forced through layer of liquid on plate
2- allow liquid to flow down via downcomer (pipe), when liquid rises it overflows, water flows down & ethanol goes up in vapour, double separation, # of plates have cumulative effects, with 40 plates water/ethanol mix can reach 97.3% abv
Packed columns
Filled with bits of material (metal or glass), create large SA, vapours rise through & partly condense on surfaces, rate of condensation increases as temp decreases with height, each small pocket reflux can occur, less ordered reactions but so many is possible to make highly rectified spirit, used in trad Chinese stills for baijiu, not widely used elsewhere, some in multiple column distillation (de-methylisers)
Condensers
Not every column still needs but common, worm tub condensers rare but variation in Armagnac, shell & tube condensers & dephlegmators widely seen
Running continuously
Example with 40 plates, preheated fermented liquid enters 1/2 way up, heat input comes from steam injectors at base
Reaching dynamic equilibrium
Techniques vary, fractions are forced to keep moving up & down, in early stages fractions on each plate constantly changing, over time movement never stops but changes in conc on each plate decreases, with constant conditions you can know conc of each fraction on any plate with high accuracy
Methanol
Group-1 fraction, boils at 64.7 C (148 F), very volatile, more conc on every plate & rises, most conc at top of still
Iso-amyl alcohol
Group-3 fraction, boils at 131 C (268 F), reaches highest conc on lower plate where it’s least volatile, on higher plates is not conc & small amounts that rise up flow back down (no fraction stops part way, vapour contains multiple fractions)
Separation
Once in equilibrium each fraction reaches highest conc depending on boiling point, most volatile/lowest boiling points are most conc at top, because fractions spread across height of still is possible to take off heads, hearts, tails & liquid waste simultaneously
Maintaining equilibrium
Can be maintained indefinitely as long as conditions do not change
Temperature
Temp gradient constant otherwise composition of liquid on plates will change, if temp rises then some less volatile fractions rise in greater amounts, if temp falls these fractions flow down in greater amounts, to keep temp constant liquid entering preheated
Composition of the fermented liquid
Needs to be same or composition of fractions on plate will change
Flow rates
Volume entering must be = to volume leaving or composition of fractions on plate will change
Rectification plate designs
2 common types: Bubble cap plate & Sieve plate
Bubble cap plate
Vapours rise from boiling alcoholic liquid on bottom plate, more volatile fractions in vapours & less volatile in boiling liquid, vapours pass through hole in plate covered by bubble cap, pressure from below forces vapours into liquid on top plate & causes it to boil, vapours rise from top plate & repeats, liquid overflows to plate below, liquid prevented from falling through hole in plate by weir, set higher than top of downcomer so only goes through downcomer, bottom of downcomer submerged so min vapours passing up pipe & not reflux through liquid on plate above
Sieve plate
Movement of gas & liquid is same, only difference is how they rise up & are forced through holes in plate into liquid on plate, pressure of rising vapours keeps liquid on plate & stops from falling through holes, vapours rise up from top plate, liquid overflows to plate below, some downcomers have base within copper ‘cap’ to ensure is submerged
Single column still
Lower half- steam in & liquid waste out at bottom, called stripping section
Midway- preheated alcoholic liquid in
Upper half- rectifying section, tails, then higher up hearts, heads out at top
Double-column Coffey still
1st column- steam in & liquid waste out at bottom, preheated alcoholic liquid in at top, analyzer/stripper
2nd column- rectifier, hot vapour in & hot feints out at bottom, fermented alcoholic liquid in at top, tails out lower, higher up hearts, heads out at top
Concentration in a column
With 40 plates iso-amyl alcohol rises & falls, more volatile congeners peak on higher plates, less volatile on lower plates, most volatile at the top
Stripping section
Lower section, below point where fermented alcoholic liquid enters, aim is to separate all volatile fractions from some water & non-volatile fractions (removed at base)
Rectifying section
Volatile fractions separated out & depending on # of plates comes out high strength or neutral
Double-column still
Very tall, often divided into 2 stills linked by tubing that allows hot vapours & liquid to pass from one still to other, work same way as 1 still, pre-heated alcoholic liquid enters top of 1st still (stripping column), same as lower section of single still, 2nd still (rectifying still) performs as top section, can produce 96% abv & contain small amounts of group 1 & 3 fractions
Coffey still
1st design of a double-column still, named after Aeneas Coffey
Multiple-column stills
To produce vodkas or base spirits, selectively reduce flavour further, many setups, may include stripping column, rectifier, hydroselection column, 2nd rectifier to bring low-strength product of hydroselection back to 96% abv, de-methyliser
Stripping column
Steam injection & liquid waste at bottom, alcohol feed at side top, hot vapours out & liquid recycle in at top
Rectifying column
Hot vapours in & liquid recycle out at bottom, heads out top, high strength spirit out high at side
Hydroselection column
Steam injection in & low-strength spirit out bottom, high strength spirit in midway at side, hot water in at side top, tails out at top
2nd rectifying column
Steam injection in & liquid waste out at bottom, low strength spirits in at bottom side, high strength spirit out at side top, heads out at top
De-methylising column
High strength sprit in midway at side, reboiler at bottom, methanol out at top, final spirit out at bottom side
2 common techniques to reduce flavours
Hydroselection & de-methylising, common for neutral spirits, sometimes rum & whiskies where very clean & light styles required
Hydroselection
Reduces fusel oils, volatility depends on conc of ethanol, if highly rectified spirit reduced to 20% abv fusel oils evaporate easier, highly rectified spirit enter midway & diluted with water from above, heated with steam from below, fusel oils become volatile & rise to top, diluted spirit collected at bottom so needs to be rectified again
De-methylising
Reduces methanol, volatility depends on conc of ethanol, methanol most volatile when ethanol at high conc close to ethanol-water azeotropic limit, spirit gently heated in reboiler, steam dilutesspirit, methanol separates out over height of still & collected at top, purified neutral spirit collected at bottom, required for vodka in EU because max level legally permitted low, some fruits & potatoes make more methanol during fermentation
Hybrid stills
Modern design, can used as pot or column still, flexible, can make variety of spirits, small-scale, can experiment, may not be allowed by local laws
How they are used
Operate in batches, can’t run continuously, include pot & column still & condenser, can bypass column to use only pot still, can direct vapours from top of pot to bottom of column & use as column still
Vapour infusion box
Common feature of hybrid still, adds flavour by passing vapours through when operating as pot still, expensive to retrofit
Column still using hybrid still- setting up
Pot filled & turned on, most use steam jacket or heated water bath (less $), dephlegmator at top turned on to coldest setting & heat to pot turned on, once liquid boils vapours directed to bottom of column, very little gets past dephlegmator & fractions move up & down until equilibrium, liquid that collects at bottom flows back into pot, group 1 fractions conc at top, using time or temp to inform distiller that this has happened they increase temp of dephlegmator & vapours pass into condenser to be collected
Collecting spirit
Cont as pot still, forces group 1 fractions to top, 1st liquid collected is heads, after a few minutes cut to hearts, after a few hours temp in column rises, bottom plate sees this 1st, then one above, indicates that vapour entering bottom has lower level of ethanol & higher group 3 fractions, before there is temp change at top is cut to tails, where cut depends on the style
Differences with pot still distillation
1- presence of plates means that spirit 1st collected is much higher strength, initial flow from 10-12 plates can be higher than 90% abv
2- control of including or excluding fractions is higher, control of reflux in pot is less, hybrid still with rectification plates & dephlegmator can separate fractions more precisely
Quality of product
More control- can make spirits with great clarity, definition & purity, desirable in fruit spirits, flexibility makes them attractive to craft distillers, with enough plates can make vodka from scratch
Hybrid still producers
Most made in Germany, 2 largest- Arnold Holstein & Carl
Common features
Steam in & out, discharge outlet, steam jacket, charging line (top of pot) & pipe to feed liquid back, stirrer (electric, reduces scorching), switches at top of pot (direct flow), can have piping bypassing column to vapour infusion box to dephlegmator at top of column, otherwise piping to column at bottom, coolant in & out at top (dephlegmator), condenser (shell & tube, coolant in & out), output
