It is not necessary to knock back dough simply to deflate it, as the act of shaping the dough will quickly expel most of the gas. However, by breaking up the gluten structure, knocking back can encourage more and smaller gas cells to form, giving a closer and more even crumb texture. It can also redistribute unfermented sugars in the dough, making them more readily available for the yeast to metabolise during proving. If a more open, random crumb structure is desired, the baker will leave this step out.
Want to find out more? Look at the chapter on rising, proving and fermentation in the book flour and water.
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