I usually do an hour or two depending on a few things such as:
- Type of substrate and contamination risk, things are all pretty much in the area of mushroom advantage until you start supplementing and then all sorts of fungi and bacteria can move in hard and fast, so longer cooks for richer mixes. Longer for denser substrates too.
- Amount loaded into the treatment space, shorter for less longer for more.
- How much inoculant I plan on using, i.e. can inoculate higher into more contam. prone / rich mixes.
My 'steaming' is in a large drum with lid more or less fully on (slightly ajar just to not build up pressure, but closed enough to build up good wet heat but retain heat and moisture too) with a rack supported above an inch or two of water (or whatever is needed for the whole cook, but you don't need huge amounts) in the base, heated by those large black gas camping ring burners. I like it as I use very little water and it heats up quick.
I'd probably go the longer 2 hours for a supplemented shiitake block, don't pack it too hard so you get good steam penetration.