As mentioned above, I keep all of my grain in sealed plastic containers or mason jars. Vittles Vaults for the 55 lb. sacks, smaller containers for the smaller quantities. I've had one or two infestations in individual containers, but they didn't spread, thankfully! If I spot an infestation, I'll brew with the grain sooner than later, or otherwise just throw it out. When handling infested grain samples, I'm pretty careful to do so only well away from the other grains! And, I give all containers a very thorough cleaning between uses. It's probably a bit overboard, but I get annoyed if bugs get into the works!