W - like washback

What is a washback?

A washback is a large container or tank used in the production of whiskey. The German term for a washback is Gärbottich.

What happens in a washback?

In a washback, alcoholic fermentation, also called fermentation, takes place. During this process, the sugars and amino acids dissolved in the aqueous wort are biochemically converted into alcohol (ethanol), carbon dioxide and a number of different aroma substances by the addition of yeast with the development of heat.

What does a washback consist of?

Two types of washbacks are used in the whiskey industry. They are either made of stainless steel or wood. At St. Kilian Distillers, the washbacks are made of Douglas fir wood. This is also known as Oregon Pine, as this coniferous tree grows mainly in the western regions of North America. The individual staves are held together by iron rings to ensure the tightness of the fermenters. In addition, reed strips between the individual staves provide an additional seal. In case of longer downtimes of the washbacks, the addition of water is necessary to keep the wooden staves in their swollen state and thus ensure the tightness of the fermenters. All four washbacks each have a lid composed of several parts, which is made of spruce wood.

Where do the washbacks come from?

The four fermentation vats at St. Kilian Distillers come from Scotland. The Joseph Brown (JB) Vats company from Dufftown in the heart of Speyside built these washbacks, each with a capacity of 10,800 liters. Once completed, they were transported directly to Rüdenau by low-loader, mounted on steel platforms and connected to the distillery's piping system.

What is special about the washbacks?

At St. Kilian, we have made some additional installations in our washbacks. An agitator at the bottom of the fermentation vats ensures better homogeneity and thus ideal distribution of the yeast in the fermentation vat so that the yeast cells can do their biochemical work optimally. The agitators are designed to be very gentle and to rotate slowly. This minimizes shear forces on both the wash and the yeast. By means of two built-in stainless steel cooling plates, it is possible to maintain the perfect fermentation temperature for us during fermentation. There is also a thermal sensor on the side of the staves that measures the temperature in the wash and sends a signal to the cooling plates if necessary so that the fermentation temperature can be readjusted. The foam produced during fermentation is mechanically broken up by means of a rotating iron pipe above the liquid level to prevent possible overfoaming of the washback. After fermentation, the yeast cells at the bottom are stirred up by the built-in agitator, which facilitates pumping off the resulting beer, which is about eight percent alcohol.

What is carbon dioxide?

Carbon dioxide (colloquially, actually carbon dioxide) is a gas produced as a by-product of alcoholic fermentation. It is colorless, odorless and tasteless. However, carbon dioxide is harmful to health in higher concentrations: headaches occur above a level of about five percent carbon dioxide in the inhaled air. Prolonged inhalation of higher concentrations of around eight percent and more can lead to death.

How is carbon dioxide removed from washbacks?

On the side of our wooden washbacks there are several connections with pipes that lead into a larger collection pipe. Via this collection pipe and its gradient, the carbon dioxide, which is heavier than air, escapes to the outside.

How are the washbacks cleaned?

After fermentation, the washbacks, which are emptied over the bottom, are first sprayed out with cold water and then cleaned with hot steam for about 30 minutes at over 85°C with the lid closed. Since the Douglas fir wood does not have an absolutely smooth surface, yeasts and bacteria - especially lactic acid bacteria - can survive this steam procedure in the microscopic holes of the wood and later, especially with our long fermentation times of 65 hours, make their contribution to the complexity of the wash.

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