The tun room houses the six great wash backs, or brewing vats.
The wort and yeast were piped into the vats where the yeast fermented the sugars into alcohol, called wash. This produced a fair amount of heat and a high froth on the top of the vats. When Dallas Dhu first opened, the mash men would keep the froth down with heather brooms.
The froth was made up of carbon dioxide produced by the yeast. Being heavier than air, this used to fill the ground floor of the tun room, making it impossible to breathe down there. For this reason a lifeline and breathing equipment were kept in a locker nearby in case of emergencies.
After a couple of days, when the wash had reached a level of between 5 and 10 per cent alcohol by volume, it was passed through to the still house.