I have a batch of cider that was in fermentation for several months. I use glass demijohns and racked 3 times so the cider is very clear. It's been about 2 months since the last racking.
When I took the demijohn out for bottling I found some white film on the top. It was not there in the previous racking. I use a siphon so I wasn't too concerned of getting it into the bottles, and the cider actually tasted great.
After three days in bottles (with sugar added for carbonation) I see white film on the top of each of the bottles, and it seems more than what I had in the demijohn, and developed fast.
I'm usually very careful about sanitizing but can't rule out some contamination.
I've read a few posts about film on top of beer but I don't know if things are different with cider...
I'm thinking of giving the bottle a jolt before opening it and letting the foam drive the film out. But will it be safe to drink?
Here's how it looks... a closeup of the top of a standard 11-oz bottle.
Edit: six days later, whatever it is does not grow any more. It seems to have captured some gas at the top at start and now it looks like film-covered bubbles.