Media fill validation

If media fill solution filtered at 60 degree centigrade and. Solution collected in 2 number pressure vessel.filled vials from 1st vessel found clear but after 4hour when we used 2nd pressure vessel then unclear with burnt particles solution seen in filled vials .there were no microbial growth found in unclear vials during incubation.but post GPT shows positive what is reason for unclear solution if it is due to overheat then it should be fail in post GPT.