Distilling

1
Distilling
Philip Meaden

• Part 1 Malting, Mashing and Fermentation
• Part 2 Distillation of Malt Spirit
• Part 3 Distillation of Grain Spirit
• Part 4 Distilled Beverages other than Scotch
  Whisky
• Part 5 Flavour and Maturation
• Part 6 Cooperage
• Part 7 Blending and Packaging

2
Part 1 Malting, Mashing and Fermentation
3
Malting of Barley
Storage of dried barley (12 moisture) with
cooling
Steeping (to allow water uptake and to initiate
germination)
Germination
Kilning
4
Germination of Barley

• For malt whisky production
• full modification (essentially the breakdown of
  the endosperm) is necessary to maximise
  fermentable extract
• For grain whisky production
• amylolytic enzyme activity must be maximised
  since it provides the only source of enzymes in
  mashing

5
Kilning

• Distilling malt is only lightly kilned to
  maximize preservation of enzyme activity green
  (unkilned) malt may be used in some grain
  distilleries
• Peat smoke provides an important source of rich
  flavour (especially phenols, cresols and
  xylenols)
• lightly peated malt contains 1 to 5 ppm total
  phenols
• heavily peated malt contains 15 to 50 ppm total
  phenols
• SO2 may be used in indirectly-fired (or
  gas-fired) kilns to prevent nitrosamine formation
  during peating

6
Mashing for Malt Distilling

• All of the cereal used is malted barley
• A batch process using infusion mashing is
  generally used lauter tuns gaining in popularity
• Filtration is used to remove suspended solids
  from the wort (cloudy worts increase yeast growth
  and lead to higher levels of lipids)
• No wort boiling (as in brewing) so there is
  secondary conversion of carbohydrate after mashing

7
Mashing For Grain Distilling

• Typically uses 10 to 15 malted barley with the
  balance from cooked wheat or maize
• Cooked grain is mixed with water during filling
  of the mash tun to prevent an excessive rise in
  temperature
• Mashing temperature is maintained at 62 C
• to maximize amylolytic enzyme activity
• prevent loss of amylolytic enzyme activity

8
Desirable Characteristics of Distillers Yeast

• High ethanol yield
• Tolerance to ethanol and heat
• Rapid fermentation (of glucose, maltose and
  maltotriose)
• Production of the correct balance of flavour
  compounds
• High viability during storage (at 3 to 5 C)

9
Yeast Supply

• Primary yeast is
• a distilling strain of Saccharomyces cerevisiae
• propagated aerobically
• supplied as compressed (26 dry weight), creamed
  (18 dry weight) or dried (95 dry weight)
• Secondary yeast (if used) is
• spent brewers yeast (usually compressed)
• ale or lager strain
• a source of additional flavours

10
Microbiological Quality of Distillers Yeast

• High viability (gt95)
• Total bacteria -lt106 g-1 compressed yeast, lt0.6
  ? 106 g-1 cream yeast
• Lactic acid bacteria -lt30,000 g-1 compressed
  yeast, lt20,000 g-1 cream yeast
• Wild yeasts and moulds -lt10,000 g-1 compressed
  yeast, lt6,000 g-1 cream yeast
• (1 g compressed yeast ? 0.8-1.2 ? 1010 cells)
• (1 g cream yeast ? 0.6-0.8 ? 1010 cells)

11
Preparing for Fermentation
Addition of yeast5 ? 106 to 2 ? 107 cells
ml-1 Setting temperature typically 16 to 18 C
12
Washbacks (Fermentation Vessels)

• Volumes in the range 30,000 to 250,000 litres
• Traditionally constructed from wood (pine,
  larch), still in widespread use in malt
  distilleries
• wood is a good insulator, so setting temperature
  is important
• In grain distilleries, typically constructed from
  aluminium or steel
• temperature control can be used
• CO2 recovery is possible
• cleaning is more efficient

13
Cleaning and Sterilization

• Yeast batch tanks frequent cleaning with caustic
  soda or hypochlorite, followed by steam
  sterilization, is necessary
• Washback cleaned with caustic soda, and steam
  sterilized
• Wash still charger cleaning is less frequent,
  and may be carried out during shutdown periods
  only

14
The Fermentation Process

• Fermentation time minimum of 45 hours, typically
  50 to 70 hours, can be as long as 110 hours
• Larger washbacks use stirring
• to maintain even distribution of yeast and
  temperature
• to prevent buildup of solids and CO2
• Yeast growth typically 10- to 30-fold increase
  in cell number
• Temperature during fermentation reaches 34 or 35
  C, but may go higher

15
Sugar Utilization during Fermentation
16
Changes in Specific Gravity and Ethanol
Concentration During Fermentation
17
Changes in Specific Gravity and Temperature
During Fermentation
18
Changes in Specific Gravity and pH During
Fermentation
19
Growth of Lactobacilli during Fermentation
Dolan, TCS (1976) Journal of the Institute of
Brewing 82,177
20
Effects of Bacterial Spoilage

• Reduced ethanol yield
• Unwanted by-products
• acrolein (glycerol ? ?-hydroxypropionaldehyde ?
  acrolein)
• off-flavours
• nitrous gases

21
Quality Checks on Fermented Wort (Wash)

• Final gravity
• Ethanol concentration (typically 8-9, v/v)
• pH and acidity (pH 3.7 to 4.0, 0.15 to 0.30
  lactic acid)
• Analysis of residual starch and sugars
• Analysis of congeners
• ethyl acetate, n-propanol, iso-butanol, iso-amyl
  alcohol