5- The Fundamentals of Distillation

Question 1

Concentration & selection

Answer 1

Separating alcoholic medium into individual parts (fractions) & reassembling into different proportions

Question 2

Boiling & volatility

Answer 2

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

Question 3

Boiling point of water

Answer 3

At standard atmospheric pressure water boils at 100 C (212 F), gas is 100% water

Question 4

Boiling point of ethanol

Answer 4

78.3 C (173 F), gas is 100% ethanol, takes less energy to become gas so ‘more volatile’

Question 5

Boiling point of water/ethanol mixture

Answer 5

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

Question 6

Vapour

Answer 6

Boiling water has haze above, not gas, millions of tiny water droplets, there is gas but you can’t see it, combo is vapour

Question 7

Reflux

Answer 7

Vapour doesn’t behave in orderly manner, gases & droplets constantly interacting with each other & composition constantly changing, crucial process

Question 8

Heat energy

Answer 8

Mixture containing ethanol & water- both gas & droplets contain both & both relatively hot, when some gas interacts with some liquid combined heat energy shared

Question 9

2 outcomes of redistribution of heat energy

Answer 9

1- greater proportion of more volatile ethanol ends up as gas
2- greater proportion of less volatile water ends up as liquid

Question 10

Temperature gradient

Answer 10

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

Question 11

Relationship between temperature difference & amount of reflux

Answer 11

Direct relationship between size of temp difference & amount of reflux, wider temp difference- more reflux & higher abv vapour at top

Question 12

Rectification

Answer 12

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

Question 13

Azeotrope

Answer 13

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

Question 14

Fractions

Answer 14

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)

Question 15

Reflux

Answer 15

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

Question 16

Fractions in an alcoholic liquid

Answer 16

Potentially 99% made up of ethanol & water, remaining is 1000’s of fractions, many extremely aromatic when conc, 4 groups

Question 17

Group-1

Answer 17

Lowest boiling point, methanol & small # of other fractions, solventy aromas, can have physical response (shooting pain in nose), can give gritty texture

Question 18

Group-2

Answer 18

Higher boiling points than group-1, ethanol, many fractions with similar boiling point, majority give distinctive character, esters

Question 19

Group-3

Answer 19

Higher boiling points than ethanol & sometimes water, fusel alcohols (propanol, butanol, iso-amyl alcohol), cheesy, plastic aromas, can give coarse, rough texture

Question 20

Group-4

Answer 20

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

Question 21

Sour mashing

Answer 21

Common in American whiskey

Question 22

Reflux when distilling

Answer 22

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

Question 23

Maximum reflux

Answer 23

Distillers who want pure aromas & smoother texture max reflux to min group-3 fractions

Question 24

Minimum reflux

Answer 24

Spirits have wider range of aromas & sharper or coarser texture, style vs. quality

Question 25

Managing reflux

Answer 25

2 ways:
1- control amount of interaction between gases & liquids, column stills have advantage
2- control temp gradient, any type of still

Question 26

Still height

Answer 26

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

Question 27

Controlling heat input

Answer 27

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

Question 28

Dephlegmators/head condenser

Answer 28

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

Question 29

Maillard reactions

Answer 29

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

Question 30

Cognac

Answer 30

Lees distilled with wine, raises amount of amino acids, increases potential for Maillard reactions, gives richer character, more age-worthy

Question 31

Direct heating

Answer 31

Can increase Maillard reactions d/t creation of hot spots on surface of still, less likely in steam-heated still (surfaces more evenly heated)

Question 32

Plates

Answer 32

Increase amount of reflux by forcing gases & liquids in vapour to interact with each other

Question 33

Esterification

Answer 33

Esters created when fatty acid reacts with alcohol, yeast creates esters during fermentation & also release fatty acids & alcohols (further react in still)

Question 34

Standard atmospheric pressure

Answer 34

Boiling point depends on pressure, quoted at standard atmospheric pressure (1 bar), as pressure increases boiling point decreases

Question 35

Still pressure

Answer 35

Can lower pressure to create partial vacuum, creates pressure difference that would crush normal still, special stills needed to withstand

Question 36

Low-pressure still

Answer 36

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

Question 37

Japan

Answer 37

Exploit change in relationship between boiling points to separate fusel alcohols with greater degree of precision, exploit variation in Maillard reactions

Question 38

Advantages of low-pressure stills

Answer 38

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

Question 39

Disadvantages of low-pressure stills

Answer 39

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

Question 40

Sulfur compounds

Answer 40

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

Question 41

Sulfur removal

Answer 41

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

Question 42

Clay stills

Answer 42

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

Question 43

Solid-state distillation

Answer 43

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