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.