Kvasný průmysl (Nov 2001)
Development of colloidal hazes in bottled pale lager beer during ageing.
Abstract
The haze development patterns of protein - polyphenol beer colloids has been simultaneously studied at nephelometric 90° angle and forward 15° angle of scattered light, directly an intact commercially bottled 12 grade pale lager beer samples at various thermal ageing conditions. It has been discovered and proved that during the beer ageing process the size of protein - polyphenol chill haze particles is temporary growing over the one micrometer dimension and dissolves again with increasing ageing tome as indicated by the appearance of temporary forward scattering haze maximum on the haze development pattern curve. The observed effect can be explained qualitatively by the concentration growth of haze-active polyphenols, i.e. condensed flavanols in relation to the concentration of haze-active proteins. When the concentration of haze-active polyphenols reaches the equivalent concentration of haze-active proteins, the biggest haze particles are formed, thus scattering more light in forward direction. With increasing haze-active polyphenol concentration large chill haze particles are dissolved back to submicrometer size as indicated by the value of 90° nephelometric haze. The precipitation effect is supported by the presence of ethanol and low temperatures. Obtained results are suggesting that the process can be described in the first approximation by two simple irreversible subsequent kinetics. The time constant of the first one is governed by the rate of the conversion of simple flavanoids into haze-active form, indicated by the forward scattering chill haze curve and the second one is expressed by the rate of the conventional 90° nephelometric chill haze growth after the lag phase. Although the molecular mechanisms of the beer permanent haze can not yet be elucidated by the results of the presents of the present work the suggested kinetic model can be used to fit or "calibrate" the first stage of the colloidal ageing process of the particular beer brand and to improve the forecast of beer colloidal stability. At least but not last, the obtained results will be useful for further studies of the colloidal and flavour ageing processes in commercial beer brands as well as in model systems.(In Czech, English summary only)
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