Rice itself does not contain yeast, but yeast can be found in the environment and may naturally occur on the surface of rice grains. Yeast is a type of fungus that can be used in baking and fermentation to help dough rise and to create alcohol. If rice is left in a warm, moist environment, it can potentially become contaminated with yeast or other types of fungi. However, commercially produced rice is typically processed and stored in ways that prevent the growth of yeast and other microorganisms.