2.5 Batch Distillation

Question 1

ethanol boiling pt

Answer 1

78C

Question 2

Bubble pt

Answer 2

pt/temperature at when ethanol mixture begins to evaporate, meaning up to that point the mixture had remained in liquid phase (i.e. 10% beer = 93C)

Question 3

Dew pt

Answer 3

pt at which condensation of ethanol vapour condenses; alcohol conc in vapour and condensate is the same; i.e. 10% beer’s bubble pt is 93C, the dew point from there is 55% ABV, therefore, with a 10% beer, the product is 55% ABV…although that beer concentration will continually change throughout the course of distillation.

Question 4

Low wines run for pot

Answer 4

55% collection down to 1%; with 10% beer

Question 5

high wines or spirit distillation for pot

Answer 5

could collect down to 50%, resulting in ~65% ABV altogether; tails on 2nd run collected down to 1% and recycled back to next charge for re-distillation.

Question 6

Typical capacity for beer/wash still in batch

Answer 6

2000-15000L, brandy still is at the bottom end of that range and has a much shorter neck; spirit still is typically smaller

Question 7

Sight glass requirement in rum and whiskey beer/wash still?

Answer 7

needed to control frothing of fermented beer/wash with content of CO2 and surface-active components of yeast and raw materials.

Question 8

Brandy low wines?

Answer 8

Broullis

Question 9

Heating systems for batch (non direct)

Answer 9

fitted with long copper steam coils, or alternative arrangementis a single circle of pipe, fitted with vertical hollow plates (pans) which constitute most of the heat transfer area; pot must be sufficiently charges so that liquid remaining at end of distillation covers heating coils, but would typically be filled to max.

Question 10

Heating systems for batch, direct fire

Answer 10

Rare, but exists in cognac; domed base of still (now relic in non direct fire), typical now would be by gas or oil vs original solid fuel; this give high temp of copper surface vs steam, so big difference in flavor, and baking effects of high temp creates deposits which may be impossible to remove by caustic alone

Question 11

Rummager

Answer 11

large rotating brush of copper chains which scrape deposits from base of still.

Question 12

Beer pre-heat

Answer 12

common to pre-heat feed, through a heat exchanger against the flow of hot pot ale (~100C) from previous run, charge enters still at 50-60C, too low for EtOH loss;

Question 13

Heating profile

Answer 13

heating must begin immediately before solids settle on coils or base of still, once heated they are kept suspended via vigorous convection currents; rapid heating to boiling saves time, the slower rise in Temp though decreases the risk of EC carryover/ post distillation formation; must be able to decrease heat immediately and rapidly when the froth is seen in sight glass…if still is fitted with a T gauge, that provides advance warning; gradual increase in temp is necessary to maintain constant flow into spirit safe…important to maintain precise distillation rate for consistent mats of flavor congeners in successive distillations

Question 14

Issues with redistillation

Answer 14

Scotland–> requires special excise arrangement, and installation temporary pipework back to wash still.

Question 15

Frothing time

Answer 15

vigorous typically over in 30 min as CO2 is driven off and any surface active components of beer or yeast cell are inactivated; then heating can be cautiously increased to hold remaining froth just visible in sight glass or at a level lower.

Question 16

3 types of condensers

Answer 16

al typically copper: 1. shell and tube 2. Worm and tub 3. Plate heat exchanger

Question 17

Shell and tube condenser

Answer 17

copper shell encasing a bundle of copper tubes, number and length of tubes (surface area for condensation and then cooling to 20C) are calculated to match capacity and distillation rate of still.

Question 18

Worm and tub

Answer 18

spiral of copper pipe, gradually decreasing in diameter; immersed in tub of cooling water ~100m

Question 19

Plate heat exchanger

Answer 19

used in only a few distilleries

Question 20

Flavour congener components of brandy

Answer 20

mix of ethanol and water with numerous flavor congeners from both the grapes and yeast metabolism

Question 21

flavor congener components of rum/ whisky

Answer 21

mix of ethanol and water with numerous flavor congeners from raw material, yeast metabolism, and structural components from yeast, since it is not normal practice to remove prior to distillation (ie. long chain fatty acids- oleic, linoleic, and palmitic…from cell membranes)

Question 22

3 main volatility groups for congeners

Answer 22

1. those more volatile than ethanol (methanol, acetaldehyde, ethyl acetate, sulfur) 2. averaging approx. the same volatility (diacetyl, IAA, and other fusels), but technically more volatile than EtOH at low concentrations, but become less volatile as ethanol increases (very important for spirit run) 3. less volatile (phenol, long chain fatty acids)…distill slowly at first but then in increasing amts as ABV falls and temps rise

Question 23

Heads cut to spirit fraction indicators?

Answer 23

decided by time from experience of how long is required, sensory, temp/abv in-line measurement, luching test (50:50 sample with water…cloudy= still have fatty acid residue); combined with tails and then combined with low wines for next run…except in brandy, the 1st cut is discarded due to methanol

Question 24

Diff b/e cut point at 50% vs 60% ABV?

Answer 24

greater amts of 2+3 congeners are collected with 50% cut pt, particularly 3 wince they are distilling in increasing amt as ethanol drops

Question 25

Tails cut of spirit run

Answer 25

collected down to 1% and recycled with heads and combined with low wines from beer still for next run.

Question 26

Spirit safe requirements/ collection tools

Answer 26

Beer= one bowl with hydrometer (should be at 20C coming off still, or corrected with charts), for sensitivity to 1%; Spirit still = two bowls, one for accuracy at cut pt (50-60%) and one for accuracy down to 1%; water tap for misting test and swiveling spout to make cut pts

Question 27

% distillate from spirit run that is recycled

Answer 27

35-40%; some is lost –> some high volatile congeners will vent to atm, type 2 = distilled with spirit, type 3= some distilled to spirit, discharged in spent lees, or remains in still charging vessel, either coating walls or forming a separate layer of denser liquid.

Question 28

Balanced distillation

Answer 28

for each pair of stills –> both stills will run simultaneously and operated in approx. same time (4-10 hrs) where beer still run =1000L charge, and spirit still = 600 L charge (350 low wines+250 heads and tails), alternatively beer still could be ran twice (2x5hr runs) to feed spirit still of same size with a 10hr spirit run (1000L beer x 2 –> 700L low wines+250 heads and tails = 950L spirit run). 100L spirit collection

Question 29

Unbalanced distillation

Answer 29

each pairs are running at different times (out of sync); advantage = max use of stills; disadvantage= charge for each run of spirit still could have different composition, according to what was available at the time of filling, so each distillation produces sl diff flavoured spirit –> need separate low wines and heads and tails receivers to allow prep of more consistent charges with respect to both congener and alc strength; distillate combinations for one filling bond; another disad.= exhaustion of the internal surfaces of the still…also with immediate refill and restart the level of sulfur compounds in spirit rises to unacceptable levels over the course of a weeks operation…at same time, the amt of dissolved Cu falls, but gradual loss of still structure is necessary for quality spirit

Question 30

Triple distillation process

Answer 30

1. beer still –> same operation as double 2. Intermediate still –> distills only two fractions (heads/ high wines and tails), heads/high wines cut= down to much lower ABV, even down to 20%, tails are collected down to 1% and recycled to next IS run 3. Spirit still –> charge= it’s own heads and tails+ high wines from IS…much higher ABV (>50%); final spirit= much higher ABV as well (>80%).

Question 31

Triple distilled spirit is lighter b/c?

Answer 31

a. the greater rectification of 3 distillations vs 2 b. 3 opportunities rather than 2 for the copper still surfaces to remove sulfur and c. stronger spirit requires greater dilution for maturation and ultimately bottling, which further dilutes congener flavor in final product

Question 32

Pre-distillation influences on quality

Answer 32

Many different influencing factors, fermentation parameters (including cultured yeast selection), bacteria and wild yeast “contamination,” and raw material all have important effects (i.e. Cognac, Caribbean Dark rums, and Scotch)

Question 33

Important influences of Cognac

Answer 33

specific grape varieties (Ugni blanc, Folle blanche, and colombarde) are low in sugar and have high acidity, giving a sour wine of only about 8% abv which is more suitable for distillation vs stronger table wine, conc. the fruity flavors of the grapes along with the alcohol; additionally the temp of distillation encourages copper catalyzed non-enzymic esterification of alcohols with the acids from the grapes; natural inoculum of yeasts contributes to a desired complexity.

Question 34

Important influences of Caribbean dark rums

Answer 34

inoculation of the fermentation is either entirely by naturally occurring inoculum of yeasts and various bacteria or by cultured yeasts supplemented by nat inoc; although spirit retains characteristics of molasses/ cane, the congeners from the mixed culture ferm have more of an impact on aroma

Question 35

Important influences of Scotch

Answer 35

big impact on flavor= malting…specifically kilning; SMM (sulfur methyl methionine) is a precursor to DMS generated in kilning, NDMA –> carcinogen…faulty kilning practices, other malt components or derivatives: aliphatic acids and aldehydes, and strecker degradation products (amino acids to aldehydes) and Maillard reactions from kilning; Peating! –> high content of the phenolic polymer lignin, peat adds various compounds (phenol, ortho-, para-, meta-cresols, guaiacol, etc).

Question 36

Reflux effect to theoretical distillation graphs

Answer 36

distillation graphs are in practice lower than actual values as it does not take into account reflux

Question 37

Factors effecting reflux

Answer 37

1. shape of the still (onion vs straight neck, slope of lyne arm 2. additional refluxing equipment (i.e. trays in neck, use of purifier in the lyne arm) 3. the rate of distillation (slow= more reflux, fast= less reflux, but also effects copper induced reactions negatively) 4. the fill level of the still (i.e. additional air-cooled surface area with low fill) 5. the ambient temperature and 6. the cleanliness of the outer surface of the still (i.e. dull= more heat loss by convection and radiation); the first 3 are the most important

Question 38

Purifier use in lyne arm for additional reflux

Answer 38

cooling water is introduced in small condenser, condensate is returned into top of pot; adds flexibility to still by making its use optional as well as adjustment of the cooling water flow rate –> can be of particular interest in peated scotch malt whisky production to adjust high volatile peat phenol profile in final spirit.

Question 39

Reasons for copper use that are of greatest value to spirit quality

Answer 39

1. removal of sulfur compounds (main reason) 2. catalytic effects (esterification of non-enzymic fashion, and EC formation) 3. exhaustion and reactivation by resting –> increase the temp, increase the reactivity, but also increases the rate of corrosion.

Question 40

Copper for the removal of sulfur

Answer 40

reaction produces both soluble copper salts (CuSO4) and insoluble salts and complexes

Question 41

shell and tube vs worm with effect on flavor with respect to sulfur

Answer 41

worm operates at lower temps, and being a single tube, has a higher flow rate–> both factors reduce reactivity in worm, resulting in higher sulfur, for ex., however, amts are not too high in g/L range, and many sulfur congeners add a desirable note to aroma, variously described as meaty or spicy.

Question 42

Copper in spirit, co products, or waste streams

Answer 42

–> in scotch, although <10mg/L is in pot ale, up to 50mg/L ie. possible in spent lees; same reaction occurs in condenser, and some copper is in spirit, but with low temps and contact time, it is well below salable limit; also some copper is removed in maturation; pot ale, dark grains, or DDG –> need to below limit to sell as animal feed

Question 43

Exhaustion and reactivity of copper by resting

Answer 43

although longer should be allowed is possible, even 1-2 hrs of lying open to atm after each run allows oxidation reactions which reactivate the exhausted copper surfaces to copper salts which are dissolved in next sprit run of still.; generally considered that there is no need for cleaning internal surfaces of stills with caustic (batch), except for heating surfaces.