Process Control Over 4VG Content Of The Top-fermented Wheat Beer

There is a distinctive clove-like aroma in some beer styles. In most bottom-fermented beers,it is considered to be undesirable. In some top-fermented beers, however, this flavor is essential. A kind of volatile phenol called 4-Vinylguaiacol(4VG) has been reported to contribute to this aroma. And the clove-like aroma is essential to the top-fermented wheat beer. The 4VG is not native to the raw material, whereas it originates from decarboxylation of ferulic acid. Ferulic acid can be decarboxylated by thermal decomposition and specific enzymes. During brewing, 4VG can be detected in the boiled wort, and high levels 4VG shoud be detected in the beer fermented with POF+ yeasts.The yeasts are the most important material, including POF+ yeasts and POF- yeasts. In the POF+ strains, a single dominant nuclear gene, designated PAD1, encodes for ferulate decarboxylase, can increase the levels of 4VG. Every kind of yeast has a distinctive brewing character and fit to a specific brewing process. Ihe this study, three yeasts including top yeast No.303, No.354 and No.362 were identified for POF character and studied for the brewing character.In this study, the influence of four parameters including raw material mixture ratio,batch feeding temperature, boiling time and fermentation temeprature on the level of 4VG in the beer was carried through with single factor test and orthogonal experiment. Samples was took from the beer during its brewing process and detected with HPLC for the ferulic acid and 4VG level. All the rsults were conducted with the statistic software of SPSS, the relations between the parameters and the 4VG levels were found out due to the single factor test. And the optimum conditions were obtained by orthogonal experiment.Ii was found that, only the yeast No.303 is POF+ yeast among the three yeasts. The 4VG level of the beer brewed with yeast No.303 was up to 2.9mg/L and outweigh 2.5mg/L. The top yeasts are shorter in fermentation period, faster in metabolic rate and high in fermentation degree. The optimum conditions were as followed: the proportion of barley malt and wheat malt 80:20, batch feeding temperature 37oC, boiling time 90min, fermentation temeprature 20oC.