Unit 1 Flashcards
Distillation Theory
Two general comments that we can apply to all washes destined for distillation
1 - Complete fermentation
2 - Free of organoleptic faults (as much as possible for the given wash category)
Issues with unfinished wash (at distillation)
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
Key features of cereal washes
5-10% ABV
Few residual sugars
No organoleptic faults
acidic pH
Low ABV and high pH make it vulnerable to microbial contamination.
Key features of grape wash
9-11% ABV
Low levels of acetic acid and ethyl acetate (‘volatile acidity’)
No sulphur dioxide addition
Potential issues with stone fruit washes
Broken pits release amygdalin, which converts to hydrogen cyanide during fermentation and distils.
Precursor for ethyl carbamate, a carcinogen.
Key features of a sugar/molasses wash
5-12% ABV
pH above 4.0 (microbial contamination risk)
Some styles use dunder or backset.
2-3 day to 2-3 weeks fermentation
What is Dunder/Backset?
What spirits is it found in, and what are the effects?
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)
Affects of muck pits on dunder.
Produces bacteria such as ‘Clostridium saccharobutyricum’ which produces butyric acid.
High levels of organic acids and volatile compounds, which convert into esters during fermentation.
Key features of agave wash
4-5% ABV
Combination of commercial and native yeasts.
24 hour - 30 day fermentation times.
Wash faults - Ethyl acetate
- 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
Wash faults - Diacetyl
CH3-CO-CO-CH3
- 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
Wash faults - Lactic acid bacteria
- Pediococcus spp., Lactococcus spp., and Lactobacillus spp.
- Causes numerous sensory issues from high amounts of diacetyl production, acetic acid, ethyl acetate, and acrolein
Wash faults - Clostridium bacteria
- Contaminates grain-based washes
- Produces high levels of butyric acid, which has an aroma of baby vomit
Fermentation factors which might affect yeast production of higher alcohols and esthers
Temperature
Oxygen level
Amino nitrogen availability
Redox affects- NAD+ levels
Yeast genetic properties
3 primary reasons why copper is chosen as a preferred still material.
- Malleable
- Conducts heat well
- Reacts with many compounds, removing them from the spirit
Why are some condensers made with copper lining?
Good conductor - offloads more heat energy, cooling more efficiently.
Secondary benefit of copper as a still material
Catalyses some esterification reactions during distillation (some evidence to support, heat also a potential factor)
Major sulphur compounds that are of interest to distillers
- Hydrogen sulphide H2S
- Di-methyl sulphide DMS
- Di-methyl tri-sylphate DTMS
Sulphur compounds - Hydrogen sulphide H2S
Fairly volatile (might ‘blow off’ to an extent)
Low aroma threshold in the µg/L range - burnt matches and rotten eggs.
What type of spirit is Hydrogen sulphide H2S most likely to be found in?
Wine based
- fruit treated with sulphur fungal deterrent in fields
- produced by some wine yeast
Where spirits are Di-methyl sulphide and Di-methyl tri-sulphide likely to be found in?
Cereal based
- precursors in lightly kilned malts
How might brewers attempt to remove DMS and DMTS?
Extended boiling after mashing
How does copper remove sulphur compounds?
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.
Why might copper levels in pot ale and spent lees need to be monitored
If being used to produce dark grains for livestock feed.
Sulphur compounds - Di-methyl sulphide and Di-methyl tri-sulphide
DMS - canned sweetcorn aroma
DMTS - overcooked vegetable aroma - worse
Di-methyl sulphide formula
H3C-S-CH3
Di-methyl tri-sulphide formula
H,sub>3</sub>C-S-S-S-CH3
4 basic elements of a pot still
- Pot (or boiler)
- Heating element
- Neck
- Condenser
What are mezcal and shochu stills traditionally made from?
Mezcal - clay
Shochu - wood
What is the aspect ratio of a pot still? What are it’s implications?
Ratio of pot height to diameter, affecting the amount of copper surface available for interaction with vapour.
What might large stills include to increase copper contact?
Recirculation devices known as purifiers - Used in Irish whiskey production in large stills.
2 ways to increase copper contact in smaller stills?
Increase surface area to volume ratio
Increased reflux
Describe a shell and tube condenser
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.
Describe a worm tub condenser
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
What type of distillation more commonly used a worm tub/serpentine condenser?
Batch distillation
Which compound causes the ‘meaty’ aroma sometimes found in distillate from a worm and tub condenser?
2-methyl-3-furyl disulphide
(MMFDS)
Formed in the still from a combination of other sulphide compounds.
Where is copper most effective at removing sulphur in a wash still?
Condenser
Where is copper most effective at removing sulphur in a spirit still?
Pot
What sensory notes were found in 2011 to be more prominent in distillate from stainless steel stills?
Feinty
Sulphury
Meaty
Describe copper placement in continuous stills.
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)
SAQ
List 4 reasons copper is used in the production of distillation equipment
-Efficient conductor of heat
- Malleable
- Reacts to remove unwanted compounds (sulphur)
- Catalyses the formation of desirable flavour compounds
SAQ
Describe 3 sulphur compounds that are formed during fermentation that can be removed by distillation
Hydrogen sulphide - formed by wine yeast or from sulphur application to fruit.
Di-methyl sulphide
Di-methyl tri-sulphide
- found in lightly kilned cereals.
Definition of distillation
A physical separation process that uses differences in boiling point and condensation to purify substances
SAQ
Describe how you would design a spirit still to produce a distillate with a ‘sulphury’ character
ASK ALICE ABOUT CONTENT
Use wash from a wash still with a steel condenser.
Use steel and and worm and tub condenser spirit still.
CHECK WITH ALICE -DOESN’T MAKE SENSE
Define a ‘binary mixture’
2 substances that are completely miscible (mix together perfectly in all proportions) and result in a homogenous solution.
Boiling point of alcohol
78.37°C
What sort of solutions does Raoult’s Law work for?
Ideal mixtures and high mole fractions
