Abstract
Iso-alpha acids are responsible for beer bitterness, but their stability can decline during warm storage due to oxidation, thermal degradation, and interaction with dissolved oxygen. This study evaluates bitterness stability of iso-alpha acids during warm storage of packaged beer. Packaged beer samples with controlled bitterness levels were stored at moderate and elevated temperatures under defined oxygen conditions. Iso-alpha acid concentration, bitterness units, dissolved oxygen, colour change, pH, turbidity, sensory bitterness intensity, and stale flavour indicators were measured over time. The results show that warm storage accelerated iso-alpha acid degradation and reduced perceived bitterness intensity. Oxygen exposure intensified bitterness loss and increased stale flavour development. Samples packaged with lower oxygen retained bitterness more effectively even under moderate temperature stress. The study demonstrates that bitterness stability depends on protecting iso-alpha acids from thermal and oxidative damage after packaging. Proper oxygen control and cool storage improve flavour balance and shelf-life consistency.