Fermentation

Wort is the pumped into the washbacks which are large and open fermentation vessels, which can hold up to 70.000 litres and be as high as 5 or 6 m. They may be covered by detachable panels and are usually made of Oregon pine.
Some distilleries use fully closed vessels made of steel which are easier to clean.Yeast is added, being either distillers yeast or a mixture of the latest with brewer yeast, and will start fermentation. The action of yeast on wort's sugar will produce alcohol and carbon dioxide. Wort will bubble, and may even in some occasions generate strong vibrations of the washback itself in spite of its impressive size.
After about 48 hours, bubbling and fermentation are over and the wort has been transformed into wash, an alcoholic liquid of 7 to 8% vol. and not unlike a sort of crude beer, which is pumped into the wash charger.

MASHING

Grist is then mixed with hot water in the mashing machine which pours it into the mashtun, which capacity can be in excess of 25.000 litres. Three successive waters, with temperatures varying from 63 to 95°C, are used to produced a sugary liquid known as wort.

Those will be taken away at the end of the process and are excellent food for cattle.
The last water used for mashing will be directed to a tank and used as the third water of the next mashing. Wort will then travel through a heat exchanger to be cooled to about 20°C, to prevent yeast cells which will ferment it from being killed.
Traditional mashtuns may be enclosed by a copper dome so as to preserve heat which allow for a better extraction of sugars contained in the malt.

mashtun : cuve
wort : le mout
cattle : brassage
yeast cells : cellule de levure
copper dome : dome en cuivre