'The brewing process proper starts in the Brewhouse. The malted and roasted barley is mixed and milled together to produce the course Guinness grist. The grist then heads to the mash vessel, where it is mixed with water heated to 65°C. This is the perfect temperature for optimal enzyme activity, enabling the starches contained in the barley to be converted into sugars.'

The first part of the 'The Brewing Process',
from The World of Guinness