Fruit flies in my mycelium - help!

I’ve got two indoor containers with king oyster mushroom mycelium in it.  Both are infested with fruit flies, as it seems.  The mycelium looks fine and healthy, but I don’t want a fruit fly infestation in the house.  I’m planning to throw out the worst one (swarming with larvae), but is there some way to prevent this from happening again?  Or to get rid of the fruit fly larvae infesting those coffee grounds without throwing out the mycelium?  Halp?

Hm… can you seal them up so they can't get out? Some cloth, so a bit of air can get to the fungi?

I already did that, but wouldn’t I need to open it when it’s time for the mushrooms to fruit?  

I did not consider that.

How about "releasing" the fruit flies outside once they hatch?

Oh no! Keep it outside in a carton box. Or in a cellar somewhere. Or quietly hide them in your muckiest friend's house cupboard in the back.

The mushroom fly larvae do the damage. Commercial button mushroom farmers use spray to control them. I would toss the substrate. Burn it, bury it, drown it as far from your grow area as possible. Then clean your grow space. When you think its clean; clean it again.  What are you using for substrate?  Flies usually originate from improperly prepared substrate.

The really badly infested one is coffee grounds.  The other one was a mix of coffee grounds and wheat bran.  I think I got rid of all the larvae in that one (my kid and I spent a few days picking out the pupae with tweezers), but the other one is in a jar and we can’t get at the bugs as easily.  I will toss that one.  

Thanks for the advice!

I know some people have great success with coffee grounds but I've never tried them.  

Increase temp and lower moisture then you'll get rid of flies

I had to post an update - I decided not to throw away the infested mycelium.  Instead, I put it outside so the fruit flies wouldn’t be in the house.  

Well, I’m getting pinning.  Tiny little baby mushrooms with tiny little baby caps.  I have no idea what will happen with them, but for now I’m terribly impressed and surprised.