To allow room for the pre-ferment to rise, the ingredients are mixed in a container at least four or five times their volume. This is about the point in time when some process similarities of yeast pre-ferments to sourdough or levain starters begins to diverge. The typical amounts of time allotted for the yeast pre-ferment period may range from 2–16 hours, depending on the dough's temperature and the added amount of viable yeast, often expressed as a bakers' percentage. Spontaneous sourdough starters take, at a minimum, several days, and are subject to many variables.