Relationship Between Premature Yeast Flocculation (PYF) Factor Of Malt And Flocculation Of Brewer's Yeast

Brewing yeast flocculation is an important feature of beer bottom fermentation. Brewing yeast flocculation plays a vital role in the beer production. Brewing yeast flocculation which is too strong or too weak will have a negative impact on the beer production process and the quality of final beer product. If Brewing yeast flocculation is too strong, yeast would flocculate in advance during the fermentation process, which would lead to some fermentable sugars still present, the reduction delay of diacetyl and acetaldehyde, as well as the prolongation of fermentation period.Some literatures results show that yeast premature flocculation is related to malt quality, and there is a premature yeast flocculation factor (in short PYF as follows) in malt. This article is aimed to establish a scientific and sensitive, rapid and accurate method to evaluate and detect the PYF factor, and then systematically determine and analyze the difference of PYF factors among the different malts supplied by the different manufacturers, different seasons of the same manufacturers, as well as statistical analysis of the relationship between malt and yeast flocculation based on beer production-scale.The following factors had been taken into consideration to set up a method to analyze the PYF factor: the initial concentration of yeast's suspension, the optimum range of pH value of buffer, the difference of water quality, PYF factor extraction methods, as well as the proportion of the reaction system components. The optimized specific parameters of the activity of the PYF factor were as follows: selection of pH 3.90, 50 mmol/L sodium acetate -acetic acid buffer with 0.1 % calcium chloride.The analysis results showed that the activity of PYF factors which was too high would lead to a faster rate of yeast flocculation, and too low would delay the rate of yeast's sedimentation after systematically compared the yeast flocculation rate changing with the malt consisted of significant differences of the content of PYF factor. In addition, the results showed that raw materials of barley played a more notable role in the content of PYF factor in the finished malt product based on monitoring the process of malting and the content of PYF factor analysis.In consideration of the important effect of the content of PYF factor on consistent beer fermentation, brewer master should analyze the content of PYF factor of different batch of malts, and adjust the ratio of different malts with the content of PYF factor in order to keep good fermentation performance of brewing yeast. Only in this way, beer with stable quality can be produced.