A carbohydrate, like starch or sugar, is transformed into an alcohol or an acid during the metabolic process called fermentation. A washback is a tall, cylindrical vessel where fermentation is carried out. The temperature of our washbacks is carefully observed to control the multiplication of the yeast and fermentation process. Distillers usually maintain an optimal temperature of approximately 35 degrees Celsius. If the temperature increases beyond this, the heat will kill the yeast. The sugary ‘wort’ liquid from the mashtun is filled into the washbacks, where yeast is added which turns the sugars in the wort into alcohol. The end result is the 'wash,' similar to beer, with an ABV of  around 9.5%.

Traditionally, washbacks were made from wood, in contrast to the stainless steel washbacks of today. Oregon Pine, Douglas Fir and European Larch were the common wood types used due to their tight grain structure and  lack of knots. There is an argument that wooden washbacks have an advantage over steel because the warmer, insulating wood influences the fermentation and flavour due to the presence of microbes and micro-fauna.