Unit 1

Question 1

Two general comments that we can apply to all washes destined for distillation

Answer 1

1 - Complete fermentation
2 - Free of organoleptic faults (as much as possible for the given wash category)

Question 2

Issues with unfinished wash (at distillation)

Answer 2

1 - High dissolved carbon dioxide can cause frothing
2 - Incomplete fermentation may not give all desired congeners.
3 - Residual sugars ‘bake on’ impacting flavour (and spirit character) and heat transfer
4 - Can indicate microbiological contamination

Question 3

Key features of cereal washes

Answer 3

5-10% ABV
Few residual sugars
No organoleptic faults
acidic pH
Low ABV and high pH make it vulnerable to microbial contamination.

Question 4

Key features of grape wash

Answer 4

9-11% ABV
Low levels of acetic acid and ethyl acetate (‘volatile acidity’)
No sulphur dioxide addition

Question 5

Potential issues with stone fruit washes

Answer 5

Broken pits release amygdalin, which converts to hydrogen cyanide during fermentation and distils.
Precursor for ethyl carbamate, a carcinogen.

Question 6

Key features of a sugar/molasses wash

Answer 6

5-12% ABV
pH above 4.0 (microbial contamination risk)
Some styles use dunder or backset.
2-3 day to 2-3 weeks fermentation

Question 7

What is Dunder/Backset?
What spirits is it found in, and what are the effects?

Answer 7

Found in rum and sour mash bourbon
Residual from wash still. Contains dead yeast and nutrients, quite acidic.
Lowers pH and provides nutrients (amino nitrogen) to fresh washes.
Increases ester production and lowers higher alcohol production (due to faster fermentation)

Question 8

Affects of muck pits on dunder.

Answer 8

Produces bacteria such as ‘Clostridium saccharobutyricum’ which produces butyric acid.
High levels of organic acids and volatile compounds, which convert into esters during fermentation.

Question 9

Key features of agave wash

Answer 9

4-5% ABV
Combination of commercial and native yeasts.
24 hour - 30 day fermentation times.

Question 10

Wash faults - Ethyl acetate

Answer 10

• Most common ester found in distilled spirits
• Solventy unpleasant aroma in high amounts.
• Produced by bacteria and yeast during fermentation
• Acetic acid bacteria in wash
• Hanseniospora spp. on grape skins

Question 11

Wash faults - Diacetyl
CH₃-CO-CO-CH₃

Answer 11

• Buttered popcorn or butterscotch aroma in high amounts.
• Formed from Acetolactate, Carbon dioxide + Acetoin, and 2, 3 Butanediol (from Pyruvate during ethanol production)
• Can be removed somewhat by leaving wash on the lees at 20-25°C for 24-36 hours

Question 12

Wash faults - Lactic acid bacteria

Answer 12

• Pediococcus spp., Lactococcus spp., and Lactobacillus spp.
• Causes numerous sensory issues from high amounts of diacetyl production, acetic acid, ethyl acetate, and acrolein

Question 13

Wash faults - Clostridium bacteria

Answer 13

• Contaminates grain-based washes
• Produces high levels of butyric acid, which has an aroma of baby vomit

Question 14

Fermentation factors which might affect yeast production of higher alcohols and esthers

Answer 14

Temperature
Oxygen level
Amino nitrogen availability
Redox affects- NAD+ levels
Yeast genetic properties

Question 15

3 primary reasons why copper is chosen as a preferred still material.

Answer 15

• Malleable
• Conducts heat well
• Reacts with many compounds, removing them from the spirit

Question 16

Why are some condensers made with copper lining?

Answer 16

Good conductor - offloads more heat energy, cooling more efficiently.

Question 17

Secondary benefit of copper as a still material

Answer 17

Catalyses some esterification reactions during distillation (some evidence to support, heat also a potential factor)

Question 18

Major sulphur compounds that are of interest to distillers

Answer 18

• Hydrogen sulphide H₂S
• Di-methyl sulphide DMS
• Di-methyl tri-sylphate DTMS

Question 19

Sulphur compounds - Hydrogen sulphide H₂S

Answer 19

Fairly volatile (might ‘blow off’ to an extent)
Low aroma threshold in the µg/L range - burnt matches and rotten eggs.

Question 20

What type of spirit is Hydrogen sulphide H₂S most likely to be found in?

Answer 20

Wine based
- fruit treated with sulphur fungal deterrent in fields
- produced by some wine yeast

Question 21

Where spirits are Di-methyl sulphide and Di-methyl tri-sulphide likely to be found in?

Answer 21

Cereal based
- precursors in lightly kilned malts

Question 22

How might brewers attempt to remove DMS and DMTS?

Answer 22

Extended boiling after mashing

Question 23

How does copper remove sulphur compounds?

Answer 23

hot vapour passed over the copper still forms copper salts, which largely drop down into the pot ale and spent lees.
Some might cling to internal condensers which can be removed by the cuts of the distillations.

Question 24

Why might copper levels in pot ale and spent lees need to be monitored

Answer 24

If being used to produce dark grains for livestock feed.

Question 25

_Sulphur compounds_ - Di-methyl sulphide and Di-methyl tri-sulphide

Answer 25

DMS - canned sweetcorn aroma DMTS - overcooked vegetable aroma - worse

Question 26

Di-methyl sulphide formula

Answer 26

H₃C-S-CH₃

Question 27

Di-methyl tri-sulphide formula

Answer 27

H,sub>3C-S-S-S-CH₃

Question 28

4 basic elements of a pot still

Answer 28

- Pot (or boiler) - Heating element - Neck - Condenser

Question 29

What are mezcal and shochu stills traditionally made from?

Answer 29

Mezcal - clay Shochu - wood

Question 30

What is the aspect ratio of a pot still? What are it's implications?

Answer 30

Ratio of pot height to diameter, affecting the amount of copper surface available for interaction with vapour.

Question 31

What might large stills include to increase copper contact?

Answer 31

Recirculation devices known as purifiers - Used in Irish whiskey production in large stills.

Question 32

2 ways to increase copper contact in smaller stills?

Answer 32

Increase surface area to volume ratio Increased reflux

Question 33

Describe a shell and tube condenser

Answer 33

Coolant flows through a series of tubes which vapours surrounds. Both components are commonly made from copper, and give a large contact surface area for the distillate. Produces a 'clean' spirit.

Question 34

Describe a worm tub condenser

Answer 34

Distillate flows through a coiled tube (basically an extension of the still neck) submerged in a water bath. Almost exclusively made from copper, but less surface area, so spirit retains a sulphur character

Question 35

What type of distillation more commonly used a worm tub/serpentine condenser?

Answer 35

Batch distillation

Question 36

Which compound causes the 'meaty' aroma sometimes found in distillate from a worm and tub condenser?

Answer 36

2-methyl-3-furyl disulphide (MMFDS) Formed in the still from a combination of other sulphide compounds.

Question 37

Where is copper most effective at removing sulphur in a wash still?

Answer 37

Condenser

Question 38

Where is copper most effective at removing sulphur in a spirit still?

Answer 38

Pot

Question 39

What sensory notes were found in 2011 to be more prominent in distillate from stainless steel stills?

Answer 39

Feinty Sulphury Meaty

Question 40

Describe copper placement in continuous stills.

Answer 40

Often foregone completely. When used, most often in the top sections of the column. May come in the form of copper-made bubble cap trays (bourbon) or sacrificial copper packing (replaceable)

Question 41

_SAQ_ List 4 reasons copper is used in the production of distillation equipment

Answer 41

-Efficient conductor of heat - Malleable - Reacts to remove unwanted compounds (sulphur) - Catalyses the formation of desirable flavour compounds

Question 42

_SAQ_ Describe 3 sulphur compounds that are formed during fermentation that can be removed by distillation

Answer 42

Hydrogen sulphide - formed by wine yeast or from sulphur application to fruit. Di-methyl sulphide Di-methyl tri-sulphide - found in lightly kilned cereals.

Question 43

Definition of distillation

Answer 43

A physical separation process that uses differences in boiling point and condensation to purify substances

Question 44

_SAQ_ Describe how you would design a spirit still to produce a distillate with a 'sulphury' character

Answer 44

Use wash from a wash still with a steel condenser. Use steel and and worm and tub condenser spirit still.

Question 45

Define a 'binary mixture'

Answer 45

2 substances that are completely miscible (mix together perfectly in all proportions) and result in a homogenous solution.

Question 46

Boiling point of alcohol

Answer 46

78.37°C

Question 47

What sort of solutions does Raoult's Law work for?

Answer 47

Ideal mixtures and high mole fractions

Question 48

4 Primary functions of a distillation plate

Answer 48

1 - Provide a path for higher volatility vapour to move up the distillation tower. 2 - Provide a path for lower volatility vapours to pass down the distillation tower. 3 - Provide a surface for the mixing of rising/falling vapours/liquids to exchange heat energy 4 - Provide space for the separation of vapour and liquid after mixing and heat transfer.

Question 49

4 plate designs

Answer 49

1 - Sieve 2 - Disc and doughnut 3 - Bubble cap 4 - Valve cap

Question 50

Plate designs good for solids

Answer 50

Sieve Disc and doughnut

Question 51

Benefits of sieve design

Answer 51

Simple Cheap Good for solids

Question 52

Potential issues with sieve design

Answer 52

Weeping & Entrainment if pressure is too high or low. System must be balanced

Question 53

Downside of disc and doughnut design

Answer 53

Large central hole, does not allow vapour and liquid to mix too well. Inefficient at enriching vapours.

Question 54

Pros of bubble/valve cap designs

Answer 54

Very efficient at vapour/liquid mixing Less risk of weeping

Question 55

Cons of bubble/valve cap designs

Answer 55

Expensive to construct Cannot be used with solids due to clogging.