The flavor profile of each bread is determined by its Fermentation Schedule. This specifies how long the dough is fermented and at what temperature it is maintained.
The Pain au Levain’s fermentation schedule is 2 hours @ 78°F plus 18 to 24 hours @ 50°F.
A baker uses the fermentation schedule as a guide, conditions are rarely perfect. A small variation in temperature—2 to 3 degrees higher or lower—is addressed by adjusting the corresponding fermentation time. In this case, 10 to 15 minutes shorter or longer.