An approximate shelf life prediction of elaborated lager beer in terms of degradation of its iso-α-acids

A 3-l laboratory-scale beer production protocol was designed and developed to produce beer. Concentrations of cis-/trans-iso-α-acids were quantified by HPLC. The trans-/cis-ratio varied from 0.62 to 0.49 after accelerated aging from 4 °C to 50 °C. The degradation of trans-iso-α-acids in elaborated pale lager beers followed first order reaction and this degradation conforms to the Arrhenius equation. The activation energy (E_a) and frequency factor (A) for trans-iso-α-acids in elaborated pale lager beer ranged from 69.2 kJ mol⁻¹ and 1.88 × 10¹⁰ days⁻¹ for trans-isocohumulone to 74.4 kJ mol⁻¹ and 1.3642 × 10¹¹ days⁻¹ for trans-isoadhumulone. The higher value of E_a demonstrated greater temperature sensitivity of trans-iso-α-acids during accelerated storage. The average half life of trans-iso-α-acids in elaborated pale lager beer was found to decrease from 471 days to 12 days when temperature increased from 4 °C to 40 °C. Using the activation energy of trans-α-acid degradation and the temperature profile of the accelerated aging, a mathematical model was employed to predict the loss of iso-α-acids, when the initial concentration of iso-α-acids in the product is known. The results obtained in the investigation can be of great importance to the industry in predicting the alteration of beer bitterness during warm periods and in tropical countries where summer temperature can reach 40 °C.