Why let dough rise twice?

Question

I'm just wondering, what's the point of letting dough rise twice? I've seen a bunch of recipes in the form:

1. Mix dough together and knead
2. Let it rise
3. Knead again
4. Let it rise again

Why do they do this? Doesn't kneading just push the air bubbles out?

Answer

Allowing dough to rise twice results in a finer gluten structure than allowing it to rise once. It results in a smaller crumb and prevents huge gaping airholes in your bread. The reason that you have to let it re-rise is that you just pushed all the air out with the kneading you did developing that gluten structure.

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