pgm distilling part1
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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
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