Sterile filtration versus flash pasteurization.
Compared with sterile filtration, flash pasteurisation is reputed to cause flavour deterioration and decreased nonbiological stability of beer. However, the equipment for the latter is readily cleaned and automated and the sterilisation effect is easily controlled through temperature and time. A disadvantage of sterile filtration is the impairment of head retention at the beginning of runs. A study was made of the effect of flash pasteurisation and sterile filtration on the nonbiological stability and flavour of beer by dividing the output (160 hl/h) of top fermentation beer (12% Plato) from a kieselguhr filter into equal parts passed either through a sheet filter or a flash pasteuriser for 15 to 60 sec. Preliminary trials at 7 P.U. (60 sec at 66 degrees C) and 28 P.U. (60 sec at 70 degrees C) showed that 7 P.U. was sufficient to pasteurise beer containing 5,000 yeast cells/ml, but, at a beer oxygen content of 0.5 ppm, pasteurisation with 28 P.U. affected neither flavour nor stability. By increasing the oxygen content from 0.5 to 1.5 ppm in beer stabilised with silica gel (100 g/hl), the stability after pasteurisation with 7 P.U. (66 or 70 degrees C) was impaired, but there was no difference in flavour until 4 weeks after bottling, when the beer treated at 6 degrees C was preferred. No flavour difference was found between fresh beers containing 0.15 ppm of oxygen, whether pasteurised (70 degrees C) or sterile filtered, but, after 4 weeks in bottle, both had a pronounced oxidised flavour. Shelf life was also impaired in beer pasteurised with 7 P.U. (66 or 70 degrees C) by increasing its oxygen content from 0.5 to 2.0 ppm during bottling. In a comparison of stabilisation (100 g silica gel/hl) with pasteurisation (70 P.U., 66 degrees C), there was an unexpected significant positive effect of pasteurisation on stability. In all the above pasteurisation experiments, the temperature difference between beer and hot water was 1.5 to 2.0 degrees C: increasing this difference to 6.5 to 7.0 degrees C resulted in diminished stability.
Keywords: beer filtration pasteurisation quality stability taste test