Traditional French type sourdough bread is made with a preferment (levain) step, using a combination of yeast and bacteria. The traditional approach begins with a spontaneous starter or “chef”. The chef is prepared by mixing flour and sometimes other ingredients with water and allowing the diluted mixture to spontaneously ferment.
After some time, usually more than 24 hours, the naturally occurring yeast and bacteria from the ingredients or ambient air multiply and begin producing organic acid and carbon dioxide gas (as well as other characteristic aromas).
Once gas production has stopped, flour is added to form a thick dough, and fermentation continues. After the dough has increased to two to four times its original volume, the chef is ready to use.
This process generally requires approximately three to four days of fermentation. The levain or sourdough is then prepared from the chef by adding more flour and water to form a larger dough. Consequently, the levain is maintained or “refreshed” by blending back a portion with flour and water to keep it alive and active. Fermentation time varies with temperature, from about 6 hours at 30°C (86°F) to 12 hours at 20°C (68°F). A liquid levain is sometimes also used, containing about equal amounts of flour and water.
Florapan® starter cultures can be used to eliminate the tedious and lengthy chef step and go directly to the final levain, avoiding the complex back-slopping process. With these sourdough starter cultures, a sourdough or levain can be produced in a single fermentation step.