A question regarding oxidation in fermentation under lock.

[NottsBrew]

I have made a few brews recently and have adopted the method of allowing the initial fermentation to subside in a fermentation bin (maybe 2 to 5 days) and then siphoning the beer into a closed fermentation vessel under lock in order to let the fermentation complete. That is all well and good. I have not had any problems with this method, but I would like to throw the topic open for discussion.

These are my thoughts... how effectively does the CO2 that is generated in the second (closed) fermentation vessel protect the beer from oxidation? I suppose most of the fermentation has taken place already and there may be insufficient CO2 to protect the beer from oxygen.

When I look at my beer after the fermentation is complete, there is something like an oily appearance on the surface of the beer. I actually don't think it is oil, but it does have that look. I wonder if this is the effects of oxidation?

Please feel free to address my thoughts directly or comment on the topic more broadly. I only want to get a discussion on the topic going.

 

[DoctorMick]

My understanding, which could well be completely wrong, is that as long as the yeast are active they will continue to use any oxygen in the brew (and generate co2) so any oxygen introduced during the transfer would be consumed and you would have a fresh protective layer on the top. That would of course depend on how active the yeast are when you transfer but at the times you've mentioned they should still be pretty busy.

 

[Leon103]

The oil look could be hop oil.