Study On The Premature Yeast Flocculation (PYF) Polysaccharide In Malt And The Influence Of PYF Polysaccharide On Beer Fermentation

Premature Yeast Flocculation(PYF) is a phenomenon that yeast flocculated before out of nutrition in the fermentation liquid.The yeast can not demonstrate its fermentation performance fully and the fermentation process can not go smoothly in this case.It is reported that a biomacromolecule in malt which is insensitive to external environment can induce PYF.The same batch of PYF malt were used as the starting material,the research results are as follows:1.A rapid and sensitive method to measure Premature Yeast Flocculation Activity in Malt was established on the basis of previous study by adjusting several index, such as the method of extracting the PYF polysaccharide of malt,the concentration and amount of yeast suspension,the pH and amount of buffer solution.The parallelism and stability of the new method is better than Bens and Optical Density Assay,RSD＜3%.The new method can distinguish the PYF activity of malt apparently.2.A polysaccharide named PYFâ… -â… is purified after sedimented by ethanol, remove of protein,ultrafiltration,Chromatography by DEAE-Sephadex A-25 and Sephadex G-100.The polysaccharide accelerate the flocculation of yeast apparently (F=68.90%).PYFâ… -â… is identified as the polysaccharide which can induce PYF.3.The physicochemical property and structure of PYFâ… -â… is analysed:The content of polysaccharides and proteins was 58.3%and 3.8%;the results of Sephadex G-100 chromatography and HPLC shows that PYFâ… -â… is a single component;the molecular weight of PYFâ… -â… is 13598Dr by the method of HPSEC;the monosaccharide composition of PYFâ… -â… is analysed by TLC and GC,results show that there are Arabinose,Glucose,Xylose in PYFâ… -â… ;the results of Infrared Spectroscopy show that there are the stretching vibration of O-H,the C-H stretching vibration and angle vibration of CH₃,the C-O stretching vibration of Pyran ring,the stretching vibration of S=O and the bending vibration of NH₂.The polysaccharide is identified as a protein containing polysaccharide without nucleic acid by UV.4.The effects of PYF polysaccharide in malt on beer fermentation were studied. The fermentation degree,alcohol content,the content of flavor compounds and organic acid in beer fermentation liquid were determined.Results showed that the quantity of suspended yeast cells,the fermentation degree and alcohol content decreased signifiCantly,which cause incomplete fermentation and raw material consumption;the content of diacetyl and acetaldehyde increased,the content of higher alcohols,esters,DMS and organic acids decreased,which make the change of content and ratio of flavor compounds,cause abnormal flavor of beer.5.Three methods to decrease the content of PYF potysaccharide were studied.Wash the malt:The PYF activity of malt decreased from 60%to 45%after wash the malt by water and then dry it.But the water content,colority,a-amino nitrogen, saccharification power show that the washed malt can be used to beer fermentation.Put the malt with high PYF activity and the malt With low PYF activity together, then the F value of mixed malt were determined,the result shows that the mixed malt has a proper PYF activity for fermentation.Adjust Malting Technology:shorten the time of malt steeping,decrease the steeping degree,enhance steeping ventilation,increase the germination temperature and time,lower the temperature of ventilation when excluding wet,extend the kilning time.The F of the malt produced by new technology is 72.67%(The F value of normal malt is 67.77%).The results show that three methods can decrease the PYF activity of malt apparently.