Soak the bread in the water with the yeast and sugar for 12 hours
After 12 hours, remove the bread, squeezing it as you do so, then discard so you're left with just the liquid. Loosely cover and leave the liquid to ferment at room temperature for the next two days
Reduce the liquid on the hob to a thick Marmite consistency. 4 litres of water should make about 200ml of Marmite, so it may take several hours to reduce to the right consistency
