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Distilling

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					                       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
 Part 1: Malting, Mashing and Fermentation


Malting and Cooking           Distillation




     Mashing                  Maturation




   Fermentation         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


Yeast batch                    Mash tun
   tank



       Acid washing   Wort cooling



                           Addition of yeast:
                Washback   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

     Carbohydrate (g/litre)
60
50                                      Glucose
40                                      Maltose
                                        Maltotriose
30
20
10
0
     0           10           20            30        40
                      Fermentation time (h)
   Changes in Specific Gravity and Ethanol
     Concentration During Fermentation

       Specific gravity   Ethanol concentration (%, v/v)
1.06                                                        7
1.05                                                        6
1.04                           Ethanol                      5
1.03                                                        4
1.02                                                        3
1.01                           Specific gravity             2
   1                                                        1
0.99                                                        0
       0       10         20       30        40        50
                     Fermentation time (h)
Changes in Specific Gravity and Temperature
           During Fermentation

       Specific gravity                  Temperature (C)
1.06
                                                            34
1.05
                                                            32
1.04                           Temperature                  30
1.03                                                        28
1.02                                                        26
1.01                           Specific gravity             24
   1                                                        22
0.99                                                        20
       0       10         20        30        40       50
                    Fermentation time (h)
 Changes in Specific Gravity and pH During
              Fermentation

       Specific gravity                          pH
1.06                                                   5.5
1.05
1.04            Specific gravity                       5
1.03                                pH                 4.5
1.02
1.01                                                   4
   1
0.99                                                   3.5
       0       10         20       30       40    50
                    Fermentation time (h)
Growth of Lactobacilli during Fermentation

      Number of lactobacilli per ml (/106)
600
500
                 Light infection
400              Heavy infection
300
200
100
  0
      0         10          20                 30                     40
                  Fermentation time (h)
                                 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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