Bread-Bakers v106.n013.3

A few bread recipes call for the initial rise, then a punch down and 
a second rise and then shaping and a third rise. Most call for only 
the first and the last. What is the purpose of the second one?

I am a retired engineer and I seek to find the whys of baking. I 
doubt that I will ever have all the answers, despite an extensive 
library of breadmaking books.

Jerry Ulett