Flavors and textures in food are made from all sorts of chemicals (sugars, fats proteins, flavenoids, acids, phenolics and more). Bacteria can break down chemicals to create new ones. Some bacteria and yeasts consume sugars and poop out alcohol. Others poop out acids that make cheeses and vinegars. Yeasts eat sugar and poop out carbon dioxide. This makes beer and champagne fizzy, or it fills bread dough with bubbles so its fluffy when you bake it.