My method for making casings is as follows:

I combine cow-shit compost, vermiculite for moisture, coco core for fiber, and a little water. Once mixed, I divide the substrate, making 2 oven bags for each casing, then bake for pasteurization, making sure to not exceed 200 degrees. After cooled, I add my colonized bird seed, using 3 jars per casing, and mix thoroughly. Casings are left to colonize in the closet, covered with aluminum foil at just above room temperature.

My question is this: What kind of precautions (other than normal sanitary measures) do I need to take to ensure that my casings do not get contaminated while colonizing? How high is the risk of contamination during this stage?

What are you colonizing? P.Cubensis? there are much easier/foolproof ways of colonizing cubies - cow-shit, even pasteurized is a little contam prone, but they will colonize it. If it's pans, you're going about it the right way. don't cover with aluminum foil though - they need to breathe. Try a 1/2 inch layer of vermiculite on top of the casing. it will keep moisture in, help keep contaminants out and provide an airy surface for gas exchange. Other than that, cross your fingers.

good luck!

JBArk