Baker’s Yeast is not an Absolutely Necessary Addition to this dough. If your rye culture is well maintained, and the three steps in the building process follow the time and temperature needs of each individual phase, the existing yeast population within the culture should be sufficient to leaven the bread without the inclusion of commercial yeast. Final fermentation may take a bit longer if the bread is leavened only by the sourdough, and the baked loaves may be slightly denser. Nevertheles