You often find the mold growing on the surface of the miso, which is not pleasant looking for sure. No need to either freak out or dump whole the miso as long as you know how to handle it correctly. Why mold growing? There are tons of microbes floating around in the air as well as things that surround us. (Even the average human has over 100 trillion microbes in and on their body) When those microbes found a cozy place to settle on, they start inhabiting what is called mold.