I am asking this because we have a situation where a perfectly good pilsner suddenly dramatically changed after it was bottled into a hazy, oxidized, hoppy mess. It was for a beer competition where they were gracious enough to give us one of the extra bottles after the fact. The change was so dramatic that many of us are wondering if they accidentally switched our beer with someone else's pale ale. The beer does not taste infected or soured, it just tastes and looks completely different. The beautiful clear straw yellow turned into a rose tinted gray haze. The light hoppiness turned into an intense fruit-forward hop aroma. The mineral and slight buttery background notes completely faded away. It just tasted more like a pale ale than a pilsner.
Anyway, we're trying to get to the bottom of this. This beer was fermented in a closed system and transferred into the serving keg in a closed system. When we bottled it, we purged the bottles with CO2. We also capped it with an oxygen barrier cap. So theoretically, it has never been exposed to oxygen. It was also filtered when transferred to the serving keg so we are also puzzled how it could become cloudy again. Could there be some mishandling of the bottles after the fact that could cause this? Can a beer become oxidized after it's been bottled? Like if it's left in a warm room or outside for long periods of time? We dropped off our beer directly with them for the competition but it was 2 weeks before judgement day.