No, any sourdough is a product of fermentation, and yeast cells are present in it without fail. Another thing is that in the process, whole classes of lactic acid bacteria are added to the yeast, which develop in a sour mixture of flour and water, and their effect on the final product, that is, bread, is very significant. Bread cannot be yeast-free, even if it is prepared with sourdough, since sourdough is, in fact, a semi-finished product obtained by fermenting the nutritional mixture with lactic acid bacteria and baker's yeast. This is because the main recipe component of starter cultures is flour, which already contains Saccharomyces yeast. Once in favorable conditions, they manifest themselves in the spontaneous process of fermentation. Thus, the microflora of starter cultures is a symbiosis between yeast and lactic acid bacteria. Yeast provides rise, loosening of the dough and the formation of a porous crumb, and lactic acid bacteria give the bread taste and aroma.