Special yeast strains (usually a brewer’s yeast and a distiller’s yeast)
are added to the malt wort shortly after the washbacks begin to fill.
The yeast metabolizes the wort sugars into ethanol, carbon dioxide,
by-products and cell material, creating a frothy, breath-catching cauldron.
Revolving switchers cut the head of froth to prevent it overflowing; in the
old days a heather broom called a besom was employed to manually beat it
back.
Fermentation typically takes 30 to 72 hours, depending on temperature and
yeast strain, and the end result is an alcoholic liquid known as wash,
around 7-10% alcohol by volume. The process is also not unlike making beer,
and the person in charge of this crucial production stage is called the
brewer. (Distillers tend to prefer, but rarely practice, a longer
fermentation. The MacTarnahan fermentations take 3 to 4 days, allowing all
of the flavors to develop, something the brewers in Portland find most
appealing.) Fermentation is also an important source of aroma and flavor
compounds in single malts, known as congeners,: higher alcohols such as
fusel oils; fatty acids; esters, which have a characteristic fruity,
fragrant aroma; and aldehydes, which impart floral, leafy aromas.
The Process
Grain content, Malting,
Grinding,
Mashing, Filtering,
Fermenting,
Distilling,
Ageing.
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