Have a batch of hefeweizen that was bottled on 3/25/2012. It has been bottle conditioning between 70-80 degrees since bottled. I used grolsch bottles - some older that I've used before, and some from a new batch I bought. Everything in the old bottles has been fine, but the beer in the new bottles loses carbonation when refrigerated. I have checked the new bottles unrefrigerated, and the beer seems fine. Could the seals on the bottles shrink because of the cold and lose their tight seal? I'm stumped. Any similar experiences or suggestions?