I did an experiment recently comparing bottling methods from my keg. I used a very hoppy beer that should show up any signs of oxidation.
I bottled 3 bottles with counter pressure fillers, pressurising the bottles with CO2 first and capping on foam once filled.
Bottle 1 was glass, with a crown cap.
Bottle 2 was Coopers PET with a new cap.
Bottle 3 was Coopers PET with a new cap, where the bottle has been filled with liquid and flushed with CO2 before filling.
The bottles sat on a room temperature shelf for 2.5 weeks before being refrigeration for 3 days before sampling.
What I found was that bottle 1 was unaffected by bottling. It was pretty much the beer from the keg, although I couldn’t compare side by side as my keg kicked straight after bottling.
Bottles 2 and 3 we’re indistinguishable from each other. Given them on their own I wouldn’t have called them oxidised, as they were only a teeny tiny bit darker than bottle 1 (to the point that it wasn’t really apparent when photographed). The fresh fruit salad aroma I got from bottle 1 was also more of an overripe fruit salad aroma.
Bottle 1 is on the left here:
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This is obviously far from conclusive, but it did show for me that for now at least I’m better off filling into crown capped glass bottles for now rather than PET to keep beer fresh. I believe that the oxygen absorbing liner in the crown cap is more effective than the one in the Coopers bottle lid, but there’s a few other things that could cause the difference too.