The main quality challenge of beer is the change in its chemical composition during storage, which alters the sensory properties. The bitter tasting compounds trans-iso-α-acids converse into lingering and harsh bitter tasting tri- and tetracyclic degradation products. Using HPLC-MS/MS analysis, the present study focused on the impact of the pH value of beer on the formation of tricyclocohumol and tricyclohumol as analytical markers of beer ageing. The results exhibited a direct correlation between the pH value and the decomposition of trans-iso-α-acids to tricyclic degradation products. Within this connection, tricyclohumol presented a further analytical marker of beer ageing, in addition to tricyclocohumol.