Usually when doing this you leave it to still air out...so I would say that is just some mycelium, which is a good thing...just turn it back into the soil really...You want it there...once there is a plant in the soil I think the mycorrhiza will be doing something elsewhere and not colonizing on top of your soil...you are supposed to turn this over and I think allow it to get sun during this cooking time...I could be wrong..not tried it, but looked into trying it...