Preliminary Study On The Impact Of Microorganism On Malt Quality In Malting

Barley is the major raw materials in beer production. Firstly, quantitative changes ofmicrobial community in malting were studied in this paper by the method of countingmedium. Experimental results are showed as follow, the quantity of bacteria>yeast>mold onthe surface of barley and internal. The quantity of microorganism correlated with variety ofbarley on the surface of barley and internal. Microorganism was from external surfaces ofbarley in malting. Steeping of barley rapidly activated the dormant microbes present in barley.The amount of bacteria increased to its maximum on the fourth day of the germination，it was5.41011cfu/g bonedry malt, but the yeast and mold on the second, it was8.7105cfu/gbonedry malt and2.1107cfu/g bonedry malt. The anmount of microorganism decreased tocertain level after kilning. The amount of microorganism of the second steeping water ishigher than the first.There were different kinds of microbial community in the steeping. The10main fungi strains in malting were separated and identified. Appropriate physical andchemical method were effective to decrease the quantity of microorganism, and no effect onthe germination rate.Mold has great effects on the malt quality in malting. Impact of mold isolated on maltquality is further studied in malting. Experimental results are showed as follow, Alternaria sp.and Fusarium sp. had adverse effects on degradation of β-glucan in malt. In the wort,significant increase in the β-glucan resulted in addition of viscosity. That they had effects onprotein solution in the malt led to Kolbach index of malt decline and α-amino nitrogendecrease. Saccharifying powers of malt added Alternaria sp. and Fusarium sp. weredecreased. Increase in turbidity of wort of malt added Alternaria sp., Penicillium oxalicum,Fusarium sp. and Rhizopus oryzae were significant. Because the mold competed with barleyfor oxygen, pH of wort was decreased and total acid of wort was increased. Colour of wortcaused by mold had bad effects on colour. It was certain that Alternaria sp., Penicilliumoxalicum, Fusarium sp. and Rhizopus oryzae were harmful microorganisms detrimental tomalt quality. Mold has greater impact on turbidity of wort of malt. High turbidity of wort results inyeast easy degenerating, and has an terrible affect on beer brewing. Lactic acid bacteria has agood inhibition of mold. The application of lactic acid bacteria to improve turbidity of wortwas investigated. Lactic acid bacteria separated and screened from malt was used as test strain.The effects of inoculum size, inoculum time, steeping temperature, steeping technology andgermination technology were also studied on turbidity of wort. According to phenotypiccharacteristics and physiological and biochemical characteristics, the results indicated thatlactic acid bacteria(S32-3) separated and screened from malt was preliminary identified asL.plantarum. The optimal inoculum size of lactic acid bacteria was105个/g dry barley in thefirst steeping water at20℃. Steeping technology:4hour of water steeping,18hours of airrest,5hour of water steeping,3hours of air rest and germination technology:20℃24h,18℃24h,16℃24h,14℃24h. The turbidity of wort in produced lactic acid bacteria maltdecreased by29.5%. Other many parameters improved significantly.