obtaining a satisfactory rise from sourdough takes longer than a dough leavened with baker's yeast because the yeast in a sourdough is less vigorous. in the presence of lactic acid bacteria, however, some sourdough yeasts have been observed to produce twice the gas of baker's yeast. the acidic conditions in sourdough, along with the bacteria also producing enzymes that break down proteins, result in weaker gluten and may produce a denser finished product.