I have a double IPA that's been sitting for 4 weeks in the primary. I dumped it on a yeast cake of a previous double that came out great. I checked it today and there is a strange film on top of the wort, its not all over it but only in parts. It is opaque but you can see it due to there be not being any reflection from light on those parts. Any ideas? I will try to take a pic later. 
