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. Nevertheless, the bread will be a tribute to the health and vigor of the sourdough culture that engendered such delicious results. Another variation to consider is the addition of 3 percent malt syrup to the final dough. The result is a subtle “bottom note” of sweetness, which enhances the natural sweetness that characterizes this bread when it is skillfully made, and is a nice counterpart to the bread’s gentle sour tang. If you try this, no change in dough hydration is necessary.