4. Green mold (Penicillium, Paecelomyces) Both of them are very similar due to their rapid growth and high number of spores produced. Penicillium likes moderate temperatures. It is seen through the packs as light green, light yellow with green or gray clusters, which resemble dust on the packs. They usually start from the bottom of the pack. Paecelomyces likes quite hot temperatures and can withstand them. It usually occurs with Shitake mushrooms and is seen as pale dust in brown and light or pale yellow. The growth of mushroom fibers and fungus fibers are distinctively visible.