I can't give you any technical explanation. But yeast uses the flour to
it's development. I have a recipe for italian bread that has a sponge that
looks like this;
2 C warm water
2 T (packets) active dry yeast
3 C all-purpose flour
So you mix that together and let it sit for 45 minutes. And it rises VERY
I also have heard that too much sugar is bad for a bread. Sort of a too
much of a good thing syndrome. This is why sweet breads have more
yeast, so they can compensate for the effect of the sugars.
Salt also hurts the yeasts ability to produce. So salt is almost invariably
added last. That gives the yeast as much lead time as possible.
I'm curious, the recipe for the Italian bread sponge is from Secrets of
a Jewish Baker, if I posted the whole recipe would that be illegal?