Does yeast need sugar?

The answer

No, yeast does not need added sugar to work. Flour contains starch, and enzymes in the flour and in the yeast break it down into simple sugars the yeast can eat, so a dough with no added sugar still rises. A pinch of sugar in the proofing water, such as the 1 teaspoon Red Star uses in half a cup of warm water, simply makes the foam easier to see. Large amounts of sugar can actually slow the rise by drawing water out of the cells.