The best substrate for these jars, in my opinion, is popcorn or even normal corn.
You are very fancy with those bags.
I think sometimes we overthink shit.
One day, I must have been stoned while I was pressure cooking my jars.
Anyway. when it got to time to innoculate them, lift up the tinfoil over each jar and give them a shot via the floss plug in the lid.
When I lifted one foil off, I saw that I never actually put a cap on one jar, I just wrapped the top the same as the others with foil.
There wasn't even more, water in the jar than the others. I took a clean lid, rinsed the inside with water from the kettle and put it on. (experiment territory at this stage) It grew just fine and happy with no issues.