Sourdough cultures are a veritable zoo of microorganisms – different strains of yeasts and lactobacillus bacteria.
They feed off sugars in the chemical process of fermentation. This process facilitates production of many types of food, such as wine, cheese, yogurt, beer and bread.
In sourdough cultures, their organisms can exist and even thrive in a highly acidic environment. Two end products of fermentation are lactic acid and acetic acid (vinegar). Acetic acid retards the growth of harmful bacteria. In addition, lactobacilli produce a natural antibiotic that kills unwelcome organisms.