Factors affecting the outcome of the acidification power test of yeast quality: Critical reappraisal

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The optimised acidification power test (APT) of brewer's yeast quality includes storing the yeast slurry at 2°C under beer (AP remains constant for up to 6 days), a 15 min sample equilibration to room temperature, decantation, and washing by triple centrifugation in deionised water. The final yeast pellet keeps its AP for up to 6 h at room temperature under water and thus the APT does not need to be performed immediately after yeast collection. The correct AP value (maximum acidification produced by given yeast) is determined at 25 ± 0.1°C in a 15 mL sample containing ≥5% glucose and ≥1.5 g yeast wet weight. The cell concentration is conveniently measured as absorbance (A 660 ). Cell flocculation and/or sedimentation that can distort APT results can be prevented by stirring the sample at ≥200 rpm. The AP of yeast of different generations used to pitch brewery fermentations in cylindroconical tanks had a very low correlation with the wort half-attenuation time (T 1/2 ) due to large scatter, while each yeast generation separately showed a clear T 1/2 -AP relationship. The lowest AP of yeast cropped from cylindroconical tanks was displayed by the first cropped fraction. Post-cropping cooling had no effect on AP. Variations in pitching yeast vitality and their effect on the outcome of a brewery fermentation can be masked by variations in pitching rate, wort composition, ambient conditions in the cylindroconical tanks and other factors.

Section: Discussionmentioning

confidence: 99%

Section: Dependence Of the Ap Value On Cell And Glucose Concentrationmentioning

confidence: 96%

Section: Temperature Dependence Of the Ap Testmentioning

confidence: 97%

Section: Determining Maximum Acidification Powermentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Optimised Acidification Power Test of Yeast Vitality and its Use in Brewing Practice

Gabriel

Dienstbier

Matoulková

et al. 2008

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The Dynamic Changes of Proton Efflux Rate in Saccharomyces pastorianus Strains During High Gravity or Very High Gravity Brewing

Zhang

Zhao

Wan

et al. 2011

The changes in the proton efflux rate (PER) during fermentation of normal gravity (NG), high gravity (HG) and very high gravity (VHG) wort by a lager yeast (Saccharomyces pastorianus) were monitored using an optimized PER test method. The values of the proton efflux rate in S. pastorianus decreased with increasing initial wort gravity. Moreover, the difference in the proton efflux rate values at the beginning of the fermentation was lower than at the end of fermentation from normal gravity to very high gravity brewing. These results demonstrated that the proton efflux rate in S. pastorianus was inhibited in the later stages of high gravity and very high gravity brewing. Furthermore, the changes of the proton efflux rate in S. pastorianus under the high ethanol concentration conditions appeared to depend on the concentration of ethanol in the fermentation liquid. A better negative correlation (P < 0.001, r = -0.95) between the ethanol concentration at >4% (w/v) and the proton efflux rate was found. The changes of the proton efflux rate in the cells treated with exogenous ethanol confirmed that higher concentrations of ethanol could significantly inhibit proton efflux in S. pastorianus. This study offers a possible way to monitor and explain the performance of yeast in the complex environment of high gravity and very high gravity brewing.

Impact of the Long-Term Maintenance Method of Brewer's Yeast on Fermentation Course, Yeast Vitality and Beer Characteristics

Matoulková

Sigler

2011

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The effect of the long-term maintenance method used with a brewer's yeast on its technological properties was determined in laboratory fermentation trials with a 12°P all-malt wort. The trials were performed at a constant temperature and under conditions of constant substrate concentration. Two cultures of a bottom fermenting yeast, Saccharomyces pastorianus RIBM 95, were tested -one culture was maintained by subculturing on wort agar slopes at 4°C and the other culture underwent a three year storage in liquid nitrogen at minus 196°C. Parameters under investigation included yeast vitality measured as acidification power (AP), fermentation time needed to reach an alcohol level of 4%, the yeast cell count, sedimentation of the yeast during the fermentation, and the production of beer flavour compounds in green beer. The yeast culture stored for three years in liquid nitrogen displayed a higher count of suspended cells, required a shorter time to attenuate the wort to produce 4% alcohol and produced a 1.5 to 2.5-fold higher concentration of a number of flavour compounds. The long-term storage method did not affect the sedimentation ability and vitality of the yeast strain tested.