first, I was them to get off sand and dirt, then slice them about 1/4" thick. the caps usually go
directly into the dehydrators as they are the most delicate. the stems (and some young caps) are laid out on brown paper and allowed to air dry for 24 hrs. that way, the dry quickly in the dehydrator which is important when you're trying to dry 10 plus pounds at a time. thye must be completly dry before being stored.
it's easy but a lot of work and very time consuming. however, when you re-hydrate mine, there is no smutzh in the water and just the taste of concentrated porcini. it's all worthwhile in the end result.