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Bourbon - Fermentation

Labrot & Graham - Fermenter

After the mash has been cooled down to approximately 25 to 30°C, it can be added with a larger amount of yeast into a fermenter in which a beer with approximately 9-10% ABV develops. Here also parts of the later developing stillage are added. The stillage is part of the much-praised Sour Mash Process, which is explained in detail later.

Wild Turkey - Yeast patterns in the fermenter

The size of the fermenters depend on the distillery; from 'large' to 'enormous'. Since the continuously working column stills can process large quantities of beer, a constant supply must be provided so that the column stills does not run empty.

Early Times - Large Fermenter

Four Roses - Fermenters made of cypress wood with stainless steel Beer Well in the back

For this reason the American distilleries possess a so-called 'Beer Well', into which those fermented contents (beer) are emptied. The Beer Well is usually made of stainless steel and is placed in the midst of the numerous fermenters. The size of the fermenters determine the size of the Beer Well. Usually is the Beer Well a third bigger than the largest fermenter, so that the column stills can continue to produce even when the pumping of beer starts late.

Four Roses - Beer Well

During the alcoholic fermentation the yeast converts the sugar to alcohol and CO2. At the same time heat is produced. The fermentation usually lasts three days. An alcohol strength of approximately 9 to 10% is reached. Few distilleries (e.g. Labrot & Graham) ferment much longer; however they also don’t get higher values than 10 to 11%. The developed product is called Beer or Distiller's Beer.

The larger a fermenting container is, the larger the heat production will be. This is because of the fact that the relationship between the surface and the volume decreases with rising fermenter size which results in the fermenting container being unable to exhaust the heat over the surface any longer. If the temperature in the fermenting container exceeds 35 to 40°C, the yeast dies gradually until the fermentation stops. Many fermenting containers therefore can be cooled with cold water.

Labrot & Graham - Cooling coils in the fermenter

The result of the fermentation is already evaluated by the distilleries Early Times or Four Roses.

The smell of the beer tells already much about the later whiskey. The brewer pays much attention to an aromatic beer, which may smell e.g. strongly of apple. If the flavour of the beer begins to decrease, it shows contamination of the yeast and a new yeast tribe has to be used for the next batch.

After the fermentation the beer is distilled into raw-whiskey.

Distillation - Back to Start