5- The Fundamentals of Distillation Flashcards
Concentration & selection
Separating alcoholic medium into individual parts (fractions) & reassembling into different proportions
Boiling & volatility
When liquid heated absorbs heat energy & gets hotter, once it reaches certain temp no longer able to absorb more heat, it heat still applied extra energy causes molecules to become gas, when heat turned off liquid stops boiling
Boiling point of water
At standard atmospheric pressure water boils at 100 C (212 F), gas is 100% water
Boiling point of ethanol
78.3 C (173 F), gas is 100% ethanol, takes less energy to become gas so ‘more volatile’
Boiling point of water/ethanol mixture
90% water/10% ethanol- 98 C (199 F), gas is 50.3% ethanol/49.7% water
50% water/50% ethanol- 82.4 C (180 F), gas is 77.6% ethanol/22.4% water
10% water/90% ethanol- 78.5 C (173 F), gas is 91.7% ethanol/8.3% water
- gas always contains greater proportion of more volatile ethanol
Vapour
Boiling water has haze above, not gas, millions of tiny water droplets, there is gas but you can’t see it, combo is vapour
Reflux
Vapour doesn’t behave in orderly manner, gases & droplets constantly interacting with each other & composition constantly changing, crucial process
Heat energy
Mixture containing ethanol & water- both gas & droplets contain both & both relatively hot, when some gas interacts with some liquid combined heat energy shared
2 outcomes of redistribution of heat energy
1- greater proportion of more volatile ethanol ends up as gas
2- greater proportion of less volatile water ends up as liquid
Temperature gradient
1 source of heat located at base (hottest), further from base is cooler- fractions with highest boiling point (water) more likely to condense back, temp gradient amplifies reflux
Relationship between temperature difference & amount of reflux
Direct relationship between size of temp difference & amount of reflux, wider temp difference- more reflux & higher abv vapour at top
Rectification
Mixture of ethanol & water, net result of reflux- composition of vapour gradually changes, gas part becomes increasingly more alcoholic & more likely to rise & leave top as spirit, droplets more likely to merge & fall back into boiling liquid, spirit with higher abv is more highly rectified
Azeotrope
Ethanol/water mixture has limit of reflux & rectification, point where no matter how much reflux takes place, droplets & gas have same composition, 97.3% abv at standard atmospheric pressure, impossible to produce pure ethanol using standard distillation techniques alone
Fractions
100’s of fractions
1- fraction present in boiling liquid is present in vapour
2- each fraction has boiling point & arranged from most volatile to least, fraction with lowest boiling point most highly conc in vapour 1st, over time each fraction will reach peak of conc in vapour (from lowest to highest boiling points)
Reflux
Greater importance with multiple fractions, necessary for rectification of ethanol & has effect on other fractions present, will be some fractions with high boiling point present in vapour but most readily condense back into liquid d/t reflux, amount of reflux has impact on style & quality
Fractions in an alcoholic liquid
Potentially 99% made up of ethanol & water, remaining is 1000’s of fractions, many extremely aromatic when conc, 4 groups
Group-1
Lowest boiling point, methanol & small # of other fractions, solventy aromas, can have physical response (shooting pain in nose), can give gritty texture
Group-2
Higher boiling points than group-1, ethanol, many fractions with similar boiling point, majority give distinctive character, esters
Group-3
Higher boiling points than ethanol & sometimes water, fusel alcohols (propanol, butanol, iso-amyl alcohol), cheesy, plastic aromas, can give coarse, rough texture
Group-4
Water & fractions that never leave still, very high boiling points- ‘non-volatile’, fatty acids stay in still making it acidic, some discard, some use to raise acidity in future fermentaion
Sour mashing
Common in American whiskey
Reflux when distilling
Amount affects amount of rectification achieved but also style, as reflux increases more group-3 fractions become liquid again & do not make it into spirit
Maximum reflux
Distillers who want pure aromas & smoother texture max reflux to min group-3 fractions
Minimum reflux
Spirits have wider range of aromas & sharper or coarser texture, style vs. quality
Managing reflux
2 ways:
1- control amount of interaction between gases & liquids, column stills have advantage
2- control temp gradient, any type of still
Still height
Further away from heat source- cooler vapours, too cool for some fractions to remain as gas & condense back into boiling liquid, more reflux takes place in tall stills, varying angle of lyne arm alters amount of reflux
Controlling heat input
Adjust to make liquid boil more or less vigorously, when boiling vigorously it bubbles up inside still & can reduce temp difference & amount of reflux, some operate at just boiling- gives more reflux, most stills have thermometers in a # of places to ensure running optimally
Dephlegmators/head condenser
Manage reflux by controlling temp at top of still, install small condenser, temp can be controlled very precisely, if dephlagmator run cold then only most volatile fractions pass through into main condenser & other fractions reflux back into still, if temp raised then more fraction pass through, mimics still height, can produce different styles with 1 still
Maillard reactions
Complex reactions when sugar reacts with amino acid, speed up as temp increases, creates flavour, by varying composition of liquid distilled, you can either increase or decrease effect
Cognac
Lees distilled with wine, raises amount of amino acids, increases potential for Maillard reactions, gives richer character, more age-worthy
Direct heating
Can increase Maillard reactions d/t creation of hot spots on surface of still, less likely in steam-heated still (surfaces more evenly heated)
Plates
Increase amount of reflux by forcing gases & liquids in vapour to interact with each other
Esterification
Esters created when fatty acid reacts with alcohol, yeast creates esters during fermentation & also release fatty acids & alcohols (further react in still)
Standard atmospheric pressure
Boiling point depends on pressure, quoted at standard atmospheric pressure (1 bar), as pressure increases boiling point decreases
Still pressure
Can lower pressure to create partial vacuum, creates pressure difference that would crush normal still, special stills needed to withstand
Low-pressure still
All fractions boil at lower temp, boiling points don’t change at same rate with change in pressure, can exploit these differences to create spirit that wouldn’t be possible under standard conditions
Japan
Exploit change in relationship between boiling points to separate fusel alcohols with greater degree of precision, exploit variation in Maillard reactions
Advantages of low-pressure stills
1- some delicate aroma compounds damaged or destroyed by temps in normal still, lower energy environment allows these to be collected
2- lower temps reduce amount of Maillard reactions
Disadvantages of low-pressure stills
Expensive to buy & run, takes a lot of energy, drop in boiling point means that condenser needs to be run at lower temps, requires specialist equipment, need higher energy & higher running costs
Sulfur compounds
Produced in small quantities during fermentation, have pronounced aromas at low levels, drains or rotting vegetables, some have soy-sauce, pickled vegetable & cooked meat aromas- positive in Asian spirits, amount of sulfur is a choice & can add complexity
Sulfur removal
Can’t be separated using distillation, in hearts, heads & tails, use copper stills- react (copper traps sulfur), new copper compounds not volatile & don’t have an aroma, need just enough copper to remove sulfur, some stainless with copper inserts, replaced when exhausted
Clay stills
Rare, ancient traditions, Mezcal or Andong soju, clay performs similar to copper, irregular surface area, lot of points where many components can react with fractions in vapours, ‘surface active’, can’t be used for large stills
Solid-state distillation
Need to separate volatile fractions from non-volatile matter by creating vapours that can be selected & conc, solids are damp & loosely formed, steam injected, once fractions vapourized by steam, distillation can continue
