I cold crashed a starter, took it out of the fridge for four hours, then pitched it. I had no visual activity (and I mean none - cap still sitting firmly on post) in my airlock after 24 hours and panicked. In a previous thread I was told it was most likely OK, just taking time to wake up. Somebody asked if I had taken a gravity reading - I hadn't, but it didn't occur to me that any significant change in gravity (as in measurable with my standard hydrometer) could be detected without corresponding co2 activity. Is that not right?