The word 酵母菌 is formed by combining three characters: 酵, meaning fermentation; 母, meaning source or mother; and 菌, meaning fungus. 酵 and 母 together create 酵母, which denotes yeast as a fermenting agent. Adding 菌 specifies that it is a fungal organism, resulting in a term that literally means "yeast fungus" and refers to the microorganism used in fermentation.