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The Alcoholic Fermentation
The Wash Backs of Glenkinchie The finished malt is cut to flour in a mill. This coarse flour is called grist and is mixed in the mash tun with hot water. If the grist is too coarse, the sugar might not be fully extracted. If the grist is too fine it might stick together and the sugar can also not be extracted to nearly 100%. The malt mash is extracted three times before the sugar water is cooled in a cooler. The first water has a temperature of about 65° C; the second time the temperature of the fresh water is increased to 80° C. The water is heated nearly to the boiling point (95° C) for the final extraction. During this third extraction, there is only very few sugar left over, which can be soluted in the water. Therefore this third water is used after a slight cooling period for the first charge of the next malt batch. The yeast may only be added after cooling the liquid down to 20° C. Otherwise the yeast would die. You add 50kg of yeast to a wash back of 13.000 litres. The residue of the mashing is brought to specialised plants, which produce animal feed by extracting the water. You can smell this plants over miles. The liquid from the mash tun is called wort by the Scottish people. It is stored in the wash backs for the next two to four days until the fermentation has finished. The yeast strains convert the sugar to alcohol and carbondioxide (CO2) during the fermentation. (CO2) is a colourless and odourless gas. In breweries and big grain distilleries, the CO2 is collected for industrial purposes. The malt distilleries are too small for an economic recovery of this gas. An exception is Tomatin, the biggest malt distillery in Scotland. The wash backs are covered with lids for preventing the penetration of vinegar bacteria and to protect the wash backs from 'boiling' over. For the last reason the wash backs also contain a horizontally rotating blade at the lid, which always cuts the foam at the top. The wash backs are normally made from Oregon Pine or Cypress wood. These species have a natural resistance against fungi. Today the distilleries change more and more to stainless steel wash backs, because you need far less chemical cleaners after a single run. The fermentation has finished after approximately 48 to 96 hours. The beer, the Scots call it wash, has an alcohol content of 8 to 9% and is ready to feed the stills. |
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