Abstract
The earliest known evidence of leavened bread comes from Egypt and China in the second and first millennia BC, although records of unleavened breads and potential flour production date back tens of thousands of years. In the 19th century, the discovery of yeast fermentation led to the development of industrial bakeries in parallel with traditional sourdough bakeries. While strains of Saccharomyces cerevisiae were selected for and became the primary yeast used in industrial breadmaking, some artisanal bakeries continued to use natural sourdough. The maintenance of these two types of bakery practices led to the evolution of two genetically and phenotypically distinct clades of Saccharomyces bakery yeast. In addition to S. cerevisiae, other yeast species are regularly found in sourdoughs, in particular yeasts of the genus Kazachstania. In the sourdough ecosystem, these yeasts interact with each other and with bacteria in a positive or negative way, depending on the species and strains involved. In both sourdough and yeasted industrial dough, traits of interest include aroma production, efficient maltose utilization, osmotolerance, desiccation resistance, and freeze tolerance. These traits have largely been explored in S. cerevisiae, but there is abundant diversity in these traits even amongst strains of S. cerevisiae, and in the handful of yeast species that have been surveyed outside of Saccharomyces. The new interest in sourdough breadmaking and the societal desire to develop more sustainable and biodiversity-friendly bakeries is now leading bakers and scientists to explore the genetic and metabolic diversity of other yeast species.