That was the question of Italian researchers. They analyzed bottle-conditioned beer and pasteurized beers which had been stored for 10 months at 20°C. Assessing the cis/trans iso-alpha acids, they found that neither pasteurization nor bottle conditioning influence the stability of cis/trans isoalpha acids. The degradation of iso-alpha acids over time for both beer types was in the range of 20%.

(from:.barthhaasgroup.com)