Distilling

• 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

Philip Meaden

Part 1: Malting, Mashing and Fermentation

Malting and Cooking

Mashing

Fermentation

Distillation

Maturation

Blending and Packaging

Malting of Barley

Storage of dried barley (~12% moisture) with cooling

Steeping (to allow water uptake and to initiate germination)

Germination

Kilning

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

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

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

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

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)

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

Microbiological Quality of Distillers’ Yeast

• High viability (>95%)

• Total bacteria -<106 g-1 compressed yeast, <0.6 106 g-1 cream yeast

• Lactic acid bacteria -<30,000 g-1 compressed yeast, <20,000 g-1 cream yeast

• Wild yeasts and moulds -<10,000 g-1 compressed yeast, <6,000 g-1 cream yeast

(1 g compressed yeast 0.8-1.2 1010 cells)

(1 g cream yeast 0.6-0.8 1010 cells)

Preparing for Fermentation

Washback

Yeast batchtank

Mash tun

Acid washing Wort cooling

Addition of yeast:5 106 to 2 107 cells ml-1

Setting temperature: typically 16 to 18 °C

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

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

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

Sugar Utilization during Fermentation

0

10

20

30

40

50

60

0 10 20 30 40Fermentation time (h)

GlucoseMaltoseMaltotriose

Carbohydrate (g/litre)

Changes in Specific Gravity and Ethanol Concentration During Fermentation

0.991

1.011.021.031.041.051.06

0 10 20 30 40 50

Fermentation time (h)

01234567

Specific gravity Ethanol concentration (%, v/v)

Ethanol

Specific gravity

Changes in Specific Gravity and Temperature During Fermentation

0.991

1.011.021.031.041.051.06

0 10 20 30 40 50

Fermentation time (h)

2022242628303234

Specific gravity Temperature (C)

Temperature

Specific gravity

Changes in Specific Gravity and pH During Fermentation

0.991

1.011.021.031.041.051.06

0 10 20 30 40 50

Fermentation time (h)

3.5

4

4.5

5

5.5Specific gravity pH

pH

Specific gravity

Growth of Lactobacilli during Fermentation

0

100

200

300

400

500

600

0 10 20 30 40

Fermentation time (h)

Light infectionHeavy infection

Number of lactobacilli per ml (/106)

Dolan, TCS (1976) Journal of the Institute of Brewing 82,177

Effects of Bacterial Spoilage

• Reduced ethanol yield

• Unwanted by-products:

– acrolein (glycerol -hydroxypropionaldehyde acrolein)

– off-flavours

– nitrous gases

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