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. Malting and Cooking Distillation Mashing Maturation Fermentation Blending and Packaging 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 (>95%) • Total bacteria -<106 g-1 compressed yeast, <0.6  106g-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)

11. Yeast batchtank Mash tun Acid washing Wort cooling Washback Preparing for Fermentation Addition of yeast:5  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 Brewing82,177

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