I'm no expert, but here are some details. If microorganisms gather on the surface of your fermented food in large enough numbers that you can see them, you hav

I'm no expert, but here are some details. If microorganisms gather on the surface of your fermented food in large enough numbers that you can see them, you have two choices: (A) try to save it, or (B) throw it out. If you don't see any, then there hasn't been an environment suitable for them to grow, meaning they aren't there in nearly enough numbers to get you sick. As far as pests, you're generally expected to cover your fermentation somehow. Something like a tea towel or cheese cloth can work, or even a pot lid, probably depending on the fermentation in question. Just follow the instructions and it should turn out okay, but I don't see any reason to keep it uncovered.