Abstract
Iso-alpha acids are the main contributors to beer bitterness, but they can degrade during storage through oxidation, light exposure, temperature stress, and interaction with beer matrix components. This study investigates iso-alpha acid degradation and bitterness stability during beer storage. Beer samples with controlled bitterness levels were stored under different temperature and light exposure conditions for defined periods. Iso-alpha acid concentration, bitterness units, dissolved oxygen, colour change, pH, turbidity, sensory bitterness intensity, and stale flavour development were monitored. The results show that higher storage temperature and oxygen exposure accelerated iso-alpha acid loss and reduced perceived bitterness stability. Light exposure intensified degradation and increased flavour instability in sensitive samples. Beers stored under low oxygen and cold conditions retained bitterness more effectively. The study demonstrates that bitterness stability depends on protecting iso-alpha acids from oxidative and thermal degradation after packaging. Better storage control supports consistent bitterness, flavour balance, and shelf-life performance.