If you are sitting comfortably, we shall begin...
First of all you want 4 holes in the tops of your lids which are going to be your innoculation holes...just a few mm's in diameter. Bang a nail through the lids of use a drill.
Next get a clean bowl to prepare your mix in. The mix will be for 4 jars but you can do as many as you want by using the ratio:
3/4 jar of vermiculite
1/4 jar BRF
1/4 jar of spring water
So...take 3 jars of vermiculite and 1 jar of BRF, mix together in a bowl. Add 1 jar of spring water and mix together well. You should be left with a light, airy mix.
Fill up the 4 jars with a 1/4" gap at the top. Don't tap down the jars or pack the substrate in, tha airier the better.
Mix a few drops of H2O2 with water and dip a cotton bud in the liquid and then wipe around the top 1/4 inch of the bare jar lid to get rid of any substrate mix and to steralise the top 1/4" of the jar.
Take plain vermiculite (not substrate mix) and fill the remaining 1/4" of the jar right up to the lid.
Using insulation tape, tape over the 4 innoculation holes and also tape around the lid/jar join. Put some tin foil over the top of the jars fastned with an elastic band. There is no way for water to get in/out of the jars so the mix will remain constant.
Fill your pressure cooker with enough water to steam for 3/4 of an hour (should say in the manual) I usually add 1 1/2-2 pints of water. Place the jars in the rack provided with the cooker or in a cloth so they don't clatter against the sides and that they are off the bottom of the pan.
Pressure cook at 15PSI for 45 mins.
Leave the jars in the p.cooker to cool for at least 8 hrs or overnight so that they cool slowly in the sterile environment of the pressure cooker.
You now have 4 sterile jars ready for innoculation :)