In addition to scaling up the amount of available starter, using a levain allows you to customize its composition for specific bread doughs. For example, if you want to bake a whole wheat bread, you might build your levain with whole wheat flour instead of whatever flour or flour blend you typically use to feed your starter.
But what if waiting four or five hours for the levain to peak isn’t going to work with your schedule? Here you can manipulate variables like the feeding ratio (starter to flour to water) and temperature to adjust the timing of mixing. For example, you can build your levain the night before mixing: By lowering the temperature and increasing the feeding ratio, the yeast and bacteria have a much larger reservoir of food to metabolize before the culture peaks, resulting in much slower fermentation. “Right before I go to bed, I’ll feed 1:10:10,” says sourdough expert Kristen Dennis. “So a massive ratio switch. I put it in a pretty cool spot, in my dining room (about 72[°F] overnight). And I’ll let it go very slowly, and by morning I have just enough time to do a quick autolyse and throw the levain on. [The levain] peaks probably about 10 or 11 hours later at that ratio.”
