Part 2: Distillation of Malt Spirit

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Part 2 Distillation of Malt Spirit
Wash Distillation
Spirit Distillation
Maturation
Blending and Packaging
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Design of Pot Stills

• Stills are constructed from copper copper is
  malleable, a good conductor of heat and important
  in flavour control
• Heat is supplied by solid fuel, steam or gas
  most are steam-heated using oil as the fuel
• Design of the swan neck and lyne arm affect
  reflux bulbous neck and upwardly inclined lyne
  arm increase reflux
• Purifier may be included in lyne arm to increase
  reflux
• Rectifying plates have been used in the swan neck
  to increase reflux

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Swan Neck Shape in Pot Stills
Ball
Lamp glass
Plain
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Wash Distillation

• The wash (typically 8-9 v/v ethanol) is used to
  charge the still to about two-thirds capacity
  wash is usually at least 48 hours old
• Boiling starts at about 92C and excessive
  frothing must be avoided to prevent foul
  distillation
• Wash pre-heating may be used to avoid fouling of
  heat transfer surfaces in the still
• Low wines are collected, initially at about 50
  v/v ethanol, falling to 1, and giving a final
  alcohol content of about 20 to 23
• Residual pot ale contains about 0.1 v/v ethanol

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Collection of the Wash Distillate

• Shell and tube condenser typically consists of
  bundles of copper tubes that carry cooling water
  this has largely replaced the traditional worm
  design
• Distillate is collected at 15-20C collection of
  distillates at gt30C results in losses by
  evaporation
• The wash safe allows the collection of the
  distillate to be carefully monitored hydrometer
  and thermometer are included
• Steam pressure gauges and temperature recorders
  are now widely employed for improved process
  control

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Spirit Distillation

• Charge contains 25-30 v/v ethanol and consists
  of low wines with foreshots and feints from
  previous distillations
• Foreshots contain oily and waxy products from the
  previous distillation (detected with the
  demisting test)
• First cut typically taken at 70-75 v/v ethanol
• Middle cut is collected as new-make spirit
• Second cut typically at 62-64 v/v ethanol, can
  be as low as 57
• Foreshots and remaining feints are combined with
  low wines for further distillation

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Important Considerations in Spirit Distillation

• First cut
• if too early, spirit becomes contaminated with
  fusel oils, ethyl acetate and other highly
  volatile esters
• if too late, ethanol will accumulate in the
  foreshots
• Second cut
• if too early, a lighter spirit will be produced
• if too late, spirit will be contaminated by
  feints (stale note, metallic after-taste)

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Congener Profiles in the Spirit Still
Ethanol More volatile than ethanol Similar
volatility to ethanol Less volatile than ethanol
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Ethanol in distillate (, v/v)
40
20
0
Time
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Analysis of New-Make Malt Spirit
Units, except for ethanol, are ppm
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By-Products of Malt Distillation

• Pot ale biological oxygen demand (BOD) is very
  high (25,000-35,000 ppm)
• combined with spent grains and dried to give dark
  grains
• sprayed on farmland
• treated in an effluent plant to reduce BOD
• discharged to sea
• Spent lees BOD is quite low (1,000-2,000 ppm)
• treated in an effluent plant
• discharged to sea