I bet you didn't put anything in the bottom of the pressure cooker. If you place your jars directly in the cooker, the heat will burn the substrate. You need to put a wash cloth in the bottom then sit your jars on that. This will prevent direct heat to the jars. Also make sure to turn your heat down once the pressure starts to release. When your substrate gets that hot, it cooks some of the nutreints out of the substrate so be prepared for slow colonization. sorry man 
The Lizard,
------------------
-------------------------
Lizard Kings can do anything.