When the grain enters the plant by auger
conveyors, it should be sifted on shaking
screens to remove any corncobs, debris, or
insects that may have found their way into
the silos. The mill room should be washed
down with water to reduce grain dust, and
approximately every 2 to 6 months, it should
be heated to 50 up to 55ºC for 30 minutes to
kill any insects that may be present.
Reduction of Microbial Contamination
Bacterial and wild yeast contamination of
the fermentation is the most important
sanitation aspect to control in whiskey pro-
duction. The source of most of the contam-
ination is the malted barley. Malt routinely
has bacterial counts of 2× 105 to 5× 108. The
malt is added at 60 to 63ºC. Thus, many of
these microbes survive to propagate during
the fermentation. Bacterial levels of the corn
and other grains added before the cooking
process or at temperatures greater than 88ºC
are not given much attention because they
are killed at these high temperatures.
The most common bacterial contaminants
includeLactobacilli, Bacilli, Pediococci, Leu-
conostoc, and Acetobacter. These microbes
propagate at the expense of yeasts. Microbial
contamination will cause plant yield to
decrease because these bacteria utilize sugar
substrates to produce compounds other than
alcohol. Many of these bacteria produce
acids, mainly lactic and acetic acid, which
can alter fermentation conditions, as well as
lower product quality. Other compounds
that can alter the consistency of the whiskey,
such as esters and aldehydes, are also pro-
duced.
The fermentation process is a rather hos-
tile environment for many microbes. Initially,
sugar concentrations may exceed 16%, which
provides for high osmotic tension. Initial pH
is between 5.0 and 5.4 for a sour mash
whiskey and, by completion, will be between
4.0 and 4.5. Final alcohol concentration is
approximately 9%, and little, if any, oxygen
will be present in this high carbon dioxide
environment. These conditions severely
restrict the types of contaminating organ-
isms that will proliferate.
Contamination of the fermentations
should be minimized. Because many bacteria
are airborne, dust is kept to a minimum by
water washing all plant surfaces (walls,
floors, etc.). Incoming shipments of malt are
probed for the determination of bacterial
counts. Most specifications limit total bacte-
rial counts to between 200,000 and
1,000,000/g.Equipment Cleaning
Large fermentation vessels (120,000 to
180,000 L) should be cleaned through filling
with hot water and detergent while steam is
spread through a CIP sparger in the center of
the tank. This process should continue for 30
minutes, at which time the tank is emptied,
rinsed with water, and steamed for 2 to 3
hours for sterilization purposes before new
mash is pumped into the vessel.
The cooling coils should keep fermenta-
tion temperatures below 32ºC. Higher tem-
peratures promote yeast cell death and
off-flavor production. These coils tend to
sustain a buildup of beer stone, which is a
hard, rocklike material composed of calcium
carbonates, phosphates, and, sometimes, sul-
fates. As this material builds on the coils,
heat transfer efficiency is reduced. To com-
bat this problem, every 6 months, the vessels
should be filled with a 1% caustic solution
(NaOH) and water, and allowed to soak for
3 days to remove the buildup.
The cookers, where the mash is prepared,
and the beer still, where the finished beer is
pumped, tend to get residual grain buildup
through continuous operation. To remedy
this, a 1% caustic solution should be pre-
pared weekly to wash the cookers, the beer
still, and all connecting lines. Some distillers