No skunking

Brewed today (finally) and took the hydro sample and put it out in the sun for a while.  50 IBUs with lots of hops gunk in it. 

Didn't skunk at all.  I thought it was the iso-alpha acids from hops that went skunk in the sun?  Is there any reason that would happen only AFTER fermentation?

I think the hops have to isomerize first.  Dod you hydrogenate the iso alpha acids?  That would prevent light struck problems.

You can google isohumulones photodegradation for more technical info.

It was post-boil, so they were iso-alpha acids by then.