Research Of The Relationship Between Barley Fungi And Premature Yeast Flocculation

There is a prevalent phenomenon existing in the process of fermentation. That isto say yeast started to flocculation though there are enough nutrient substances forliving. This phenomenon called premature yeast flocculation or PYF. Premature yeastflocculation had an effect on the quality of beer. It would lead to negative impact forsugar degradation. It can obviously slow down the speed of degradation. And evenlow availability of sugar or incomplete fermentation in brewing. What’s more, it alsocaused unclear or low alcohol beer products. It had a bad effect on the flavor of beer.There are lots of reasons for premature yeast flocculation. Many researchers devotedtheir time and spirit in this phenomenon. Recently, the main reason of premature yeastflocculation was be found. When microorganism infected barley, it would be inducedbarley shell to degradation. The infected barley shell was broken down into manyhigh molecular weight polysaccharides. These polysaccharides would be in wort aftermalting and mashing. At last, it led to heavy premature yeast flocculation. Thoughmany researches were reported that fungi could bring about premature yeastflocculation, it is still a difficult for researchers to show the relationship between fungiand premature yeast flocculation. So it is important to have a deep research onpremature yeast flocculation. Depend on the research of the relationship of barleyfungi and premeature yeast flocculation, conclusions can be drawn as the follows:1.When Beer malt was infected with fungi，it would lead to premature yeastflocculation. So it is important to study the relationship between fungi and thephenomenon of premature yeast flocculation. There are eight kinds of fungi selectedfrom PYF＋malt. These are Fusarium, Aspergillus niger, geotrichum candidum,Aspergillus flavus, Penicillium, Cladosporium tenuissimum, Alternaria tenuissimaand Rhizopus oryzae.2.In order to learn about the relationship between fungi and PYF, eight kinds offungi were inoculated into the media which prepared by malt shell and distilled water,separately, and then produced wort agreement with non-shell malt and followed on boiling, filtering, pitching yeast and testing the value of premature yeast flocculation.According to the consequences about the relationship between barley fungi andpremature yeast flocculation, conclusions can be drawn that both rhizopus oryzae andAspergillus flavus can apparently and heavily bring about premature yeastflocculation. And Fusarium can also apparently bring about premature yeastflocculation but weaker than rhizopus oryzae and Aspergillus flavus. Geotrichumcandidum and Alternaria tenuissima tend to normal fermentation. What’s more,Aspergillus niger and cladosporium tenuissimum lightly result in premature yeastflocculation. Penicillium leads to sporadic flocculation. It may be connected withstrains quantity and enzyme activity. It is necessary to deeply study.3.A deep research on the relationship between barley fungi and premature yeastflocculation had been done. Depend on the activity of enzyme which produced bybarley molds that can heavily or lightly or instability lead to premature yeastflocculation, the key enzyme to premature yeast flocculation and the level of enzymeactivity were acknowledged. In a conclusion, xylanase is more important thanglucanase on the phenomenon of premature yeast flocculation. And glucanase hardlyhas a relation to the phenomenon of premature yeast flocculation. Moreover,premature yeast flocculation would happen at100U~4000U level of xylanase activity,especially, below2200U level. However, premature yeast flocculation would nothappened when xylanase activity below100U or over4000U.4.According to this consequence a conclusion could be drawn that the ability ofleading to premature yeast flocculation of fungi from strong to weak was followed byRhizopus oryzae, Aspergillus flavus, Fusarium, Aspergillus niger, Cladosporiumtenuissimum, Penicillium, Alternaria tenuissima and geotrichum candidum.5.In the experiment of the control of premature yeast flocculation which causedby fungi, copland barley without premature yeast flocculation was adopted. Beforestarted to small-scale malting, barley without premature yeast flocculation wasinfected with quantified fungi suspension. After malting PYF values should be tested.The consequences of PYF value test were coincided with the results before. Rhizopusoryzae is the strongest fungus which could result in heavy premature yeastflocculation. However, Alternaria tenuissima and geotrichum candidum are the weakest fungus which can hardly bring about premature yeast flocculation. Only thenumber of colony of these fungi was below102orders of magnitude, could prematureyeast flocculation not be happened. In addition, malt which have heavy prematureyeast flocculation can turn to light PYF malt or non PYF malt by adding nonpremature yeast flocculation malt.It is important to study the relationship between fungi and the phenomenon ofpremature yeast flocculation. In this research, no premature yeast flocculation maltwas infected with fungi selected from malting barley or beer malt. According to a lotof tests of PYF value and xylanase enzyme activity level, the kind of fungi which canobviously lead to premature yeast flocculation can be drawn. What’s more, the abilityto bring about premature yeast flocculation of fungi from strong to weak can makesure by the probability of PYF phenomenon and xylanase enzyme activity. In addition,the control rage of fungi was also drawn. It has a full analysis to the relationshipbetween premature yeast flocculation and fungi and has a deep effect on theconnection among PYF, barley and fungi. And it is helpful to beer industry.