a warm place, or a humidity- and temperature-controlled environment. Cooler-than-room or refrigeration temperatures decelerate growth and increase the time interval, while slightly warmer temperatures accelerate growth and decrease the time interval. Too warm a temperature slows growth, while even higher temperatures will kill the yeast. Death of the yeast cells occur in the range of . When cooling a levain or sourdough pre-ferment, if the dough temperature drops below it affects the culture and leads to the loss of a particular aroma in the baked bread. 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. To make a sourdough starter from scratch, the minimum-needed ingredients are flour, water, and time. This starter is maintained with daily feedings or refreshments of fresh flour and water or, new dough. It ferments at room temperature until the desired age or minimal number of refreshments, following a refreshment schedule that may include acceleration of time intervals leading into the final dough, then is added to the final dough. When maintaining a starter's existing weight, it is advised to discard 60% (or more) of the starter, replacing that discarded dough with new dough. If an increased amount of starter is required, simply add new dough. 40-parts-to-60-parts of old-dough-to-new-dough by weight, or 2-to-3, is known as the back-slopping ratio, and changes to that ratio change the pH of the just-refreshed dough. To make a primary-culture levain, Raymond Calvel used salt, but less of it than would be typical for many final-dough formulas. See also Proofing (baking technique) Straight dough Notes References Baking Breads Leavening agents Cooking techniques fr:Levain