The wash is then transformed into new spirit by double distillation in
copper pot stills. The first distillation takes place in the wash still, and
the wash is heated to just below the boiling point of water. Vapors
containing ethanol and accompanying compounds are separated from the wash,
and are condensed into an impure distillate called low wines, around 21%
alcohol by volume (42 American Proof.) Pot ale, the residue left behind in
the wash still, is processed into animal feed.
Wash has a tendency to froth, so a sight glass is usually installed in the
still to prevent overflow into the condenser. Should this happen, the whisky
is likely to be fiery and unbalanced. In the days before sight glasses,
stills were “sounded” with a wooden ball on a chain; if the froth came
up the neck, it produced a dull note on the copper.
The low wines are then re-distilled and the process repeated in slightly
smaller spirit stills. Frothing is not a problem in the spirit stills, but
the recovery of three fractions of the distillate is of fundamental
importance in determining the quality and consistency of the single malt.
The first fraction of distillate, the foreshots or heads, contains the most
volatile compounds and strongly alcoholic first runnings. This impure
distillate is collected and re-distilled with the next charge of low wines.
The second fraction, the middle cut or heart of the run, is the potable
spirit destined for aging in oak casks. This is diverted to the spirit
receiver. The final fraction of distillate, the feints or tails, also
contains unpalatable flavors and it is sent back to join the foreshots for
re-distillation.
The stillman determines the cut points for each fraction and must do so with
great care and skill. The cut points are unique to each single malt and are
carried out under lock and key, courtesy of the Customs and Excise. This is
done inside a handsome brass and glass spirit safe, the nerve center of the
distillery. All the distillates pass through the safe and the stillman tests
and judges when to make the cuts, without ever coming into contact with the
spirit.
The copper pot stills are also unique to each distillery and their design
will affect the quantity and composition of aroma and flavor compounds in
the single malt. Stills with high necks allow less of the heavier oils to
come over for a lighter flavored, clean whisky; heavier flavors are produced
in short neck stills; and bumps, bulges and bubbles all enhance a condition
called reflux, resulting in a more complex spirit. The copper helps clear
the spirit and contributes flavor. The MacTarnahan stills have high necks
and substantial pots, with a good-sized bulge at the base of the neck. The
distillery is one of the very few in Scotland to heat the stills by direct
fire, as opposed to the more usual steam-heated coils. Steam heating,
according to The MacTarnahan distiller, “takes the guts and the body out
of a whisky.”
Single malt whisky is distilled at a lower proof than most other spirits.
This, in conjunction with the still shape, the stillman’s techniques and
the strength of the whisky determine the contribution of distillation to the
aroma and flavor of a single malt. Several hundred compounds or congeners in
various concentrations, individually and cumulatively, play a major role in
the overall character of a freshly distilled single malt. Of special
importance are the estery foreshots which contribute fruity and perfumy
aromas and flavors; and the aldehydes formed in distillation, which give
leafy, floral notes to the aroma.
The Process
Grain content,
Malting,
Grinding,
Mashing, Filtering,
Fermenting,
Distilling, Ageing.
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