Novice cooks are often afraid to attempt yeast-raised mixtures. But baking with yeast is not really difficult if you realise that yeast, unlike other raising agents, is really a living plant requiring gentle warmth in order to perform. Not enough heat and your bread will be heavy and soggy. Too much heat and the yeast will be killed. And like any other plant, yeast requires food to thrive, and this it obtains from carbohydrates in the flour and sugar, and from the moisture used in making the dough.