Prolonged yeast fermentation gives the characteristic flavour to this sourdough loaf The starter needs to begin fermenting about two days before the loaf is made.
To make the starter, begin two days before you want to make the bread. Sieve the flour into a large bowl and crumble the yeast over the surface. Heat the buttermilk or beer until lukewarm and mix into the flour using a wooden spoon until a smooth batter is formed. Cover and leave for about 8-12 hours at room temperature, or until the starter begins minutely bubbling.