I am writing to ask what made this happen. Admittedly I am new to brewing, as this is my 4th batch, but I have never heard of this happening.
I brewed an Belgian Imperial IPA. The temperature in the carboy was a little warmer than I wanted at 74*, so I thought I would wait to pitch the yeast till it dropped. In the meantime I went ahead and aerated with pure O2 for 60 seconds. About 5 minutes later I looked at the carboy and the wort was almost totally black!
I assumed it was because of the O2, so I immediately pitched the yeast (since it is OK up to 76*). It has since cleared back up to it's approximately 9 SRM.
But this is a puzzle. What happened?