An autolyse is the simple rest of flour and water, before yeast and salt are added, that lets flour fully hydrate and its gluten begin to organize on its own. During the 30 to 60 minute rest, enzymes begin breaking down starch into sugars and proteins begin linking, and the dough becomes smoother and noticeably more stretchy.
The main benefit is extensibility: dough that has been autolysed is easier to shape and holds a tighter skin. For whole-grain-heavy doughs, an overnight cold autolyse in the fridge is often worth the extra planning, because bran takes far longer to soften than white flour.
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Keep the rest to an hour at room temperature, or up to twelve hours refrigerated. Skip it entirely for very short bulk fermentations or small amounts of rye, where the benefit is minor and the schedule cost is real.