Kneading bread dough is a practice that dates back thousands of years. But why do bread makers put so much time and energy into the practice? The answer lies in the proteins contained within flour, which provide strength and structure to the bread dough.
Wheat flour contains two proteins, gliadin and glutenin, which combine form gluten. When bread dough is first mixed together, these proteins are mangled and knotted together in no particular order.
As bread dough is kneaded, these proteins line up and strands of gluten form to create a matrix within the bread dough. This matrix creates strength and structure, which traps gasses and allows the dough to rise.
Kneading by Hand
Kneading bread dough by hand is the oldest method and the easiest to control. There are several techniques to kneading dough by hand, all of which involve folding and stretching the dough repeatedly.
Kneading a basic bread dough by hand generally takes about 10 minutes to form adequate gluten. Flour can be slowly added to the dough as it is kneaded to prevent it from sticking, but care should be taken to not add too much. Adding too much flour during this process can create a stiff, dry dough. When dough has been kneaded adequately, it will have a soft, silky texture and will spring back when poked with a finger.
Dough can also be kneaded by using either a bread machine or a stand mixer with a dough hook attachment.
Bread machines are a fully automated making them fairly fool proof. Kneading with a stand mixer is much faster than kneading by hand and care should be taken to not over knead.
If kneading is required to line up proteins and form a gluten matrix, it seems counterintuitive that no-knead breads would still be able to form light, fluffy loaves, but gluten can be formed naturally.
Allowing dough to ferment for 12+ hours provides yeast and enzymes time to work their magic. Enzymes within the flour break down the knotted up proteins and the gas produced by the yeast inflates the dough, creating a sort of slow motion kneading process. Because the proteins are broken down into such small pieces by the extended enzymatic action, only a small amount of natural "kneading" is required to line them up into gluten strands. So, no-knead breads are actually more of an auto-knead bread.
What happens if a bread dough is not kneaded enough or not allowed time to auto-knead? The dough will not have enough strength to hold its shape as it inflates from yeast gasses. Instead of inflating up and out, the dough will spread in a flat, outward direction. The dough may fall back on itself and collapse as the gases produced by yeast escape the dough. Baked loaves that have been under kneaded will be flat and dense in texture.