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 Mash Tun at Bowmore |
Think of an old-fashioned teapot, the sort your grannie had before they invented tea bags. Add a device to its floor that stirs up the tea leaves as they brew. Finally, make it much bigger, and make it from steel or iron rather than china. Congratulations, you have just built a mash tun...
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 Highland Park's Mash Tun |
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 Dallas Dhu |
The powdered barley from the mills is fed into the mash tun together with a charge of water at 64°C. This temperature is high enough to dissolve many of the sugars in the powder, but just low enough to allow the enzymes in the barley to continue the chemical processes begun during germination.
The mix is continuously agitated by the stirrer circulating just above the floor of the mash tun for about half an hour. The liquid, the wort, is then drained away to a tank called the underback.
More water, this time at a higher temperature, is added to the mash tun to dissolve still more of the sugars in the powder. This, too, is drained off to the underback where, mixed with the first brew, it becomes the starting point for the brewing process.
A final charge of water at a temperature of around 90°C is added to the mash tun to dissolve anything worthwhile still left in the residue for 15 minutes. This water, known as "sparging" is then drained off and is subsequently used as the first charge of water to be added to the next batch of milled barley.
The residue, called draff, is cleared out of the mash tun (by shovel at Edradour) and taken away to be used as animal feed. The process then begins all over again, using a fresh batch of milled barley and reusing the sparging from the last run at 64°C to begin the next brew.
All distilleries have at least one mash tun, while some have two. They are usually made from stainless steel to ease cleaning though some, like that at Dallas Dhu are made from sections of cast iron bolted together: a tribute to the Victorian engineering that probably produced them, but presumably more difficult to keep clean.
