• KSBB Journal
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• v.15 no.5
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• pp.438-443
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• 2000

Continuous processes using immobilized yeast were investigated in order to shorten beer maturation time. Three silica-based ceramic media and one cellulose-based medium were used. Diacetyl (DA) was one of the most distinctive compounds causing immature flavors. Heat treatment of green beer (GB) to convert a-acetolactate to DA was essential to shorten the time for beer maturation. The longer heat treatment time was needed at the lower temperature. Oxygen concentration in GB had a large influence on the conversion of a-acetolactate to DA. The lower the oxygen concentration in GB, the lower conversion ratio to DA. Heat treated GB was fed continuously to four kinds of immobilized yeast columns. DA concentration after immobilization columns was reduced to less than 0.1ppm at $3∼5^{\circ}C$ 180∼150 minutes retention time in all columns tested. This concentration is enough to fit the quality speification of commercialized product. Formation of a-acetolactate from residual sugars was higher in ceramic media column than cellulose media cloumn. The taste of beers from test processes were not the same as that of traditionally produced beer, but no off-flavors were detected in test samples, which shows that immobilized yeast columns have potentials as rapid processes for beer maturation.

• Microbiology and Biotechnology Letters
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• v.50 no.3
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• pp.404-413
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• 2022

The process of manufacturing craft beer involves a wide variety of spontaneous microorganisms, acting in different stages of the brewing process, that contribute to the distinctive characteristics of each style. The objective of this work was to compare the structure of microbial communities associated with two different craft beer styles (Doppelbock and Märzen lagers), at a late maturation stage, and to identify discriminative, or style-specific taxa. Bacterial and fungal microbial communities were analyzed by Illumina sequencing of 16S rRNA gene of prokaryotes and the ITS 2 spacer of fungi (eukaryotes). Fungal communities in maturating beer were dominated by the yeast Dekkera, and by lactic acid (Lactobacillus and Pediococcus) and acetic acid (Acetobacter) bacteria. The Doppelbock barrels presented more rich and diverse fungal communities. The Märzen barrels were more variable in terms of structure and composition of fungal and bacterial communities, with occurrence of exclusive taxa of fungi (Aspergillus sp.) and bacteria (L. kimchicus). Minority bacterial taxa, differently represented in the microbiome of each barrel, may underlie the variability between barrels and ultimately, the distinctive traits of each style. The composition of the microbial communities indicates that in addition to differences related to upstream stages of the brewing process, the contact with the wood barrels may contribute to the definition of style-specific microbiological traits.

• Journal of Microbiology and Biotechnology
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• v.20 no.4
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• pp.767-774
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• 2010

In this study, the problems of high caloric content, increased maturation time, and off-flavors in commercial beer manufacture arising from residual sugar, diacetyl, and acetaldehyde levels were addressed. A recombinant industrial brewing yeast strain (TQ1) was generated from T1 [Lipomyces starkeyi dextranase gene (LSD1) introduced, ${\alpha}$-acetohydroxyacid synthase gene (ILV2) disrupted] by introducing Saccharomyces cerevisiae glucoamylase (SGA1) and a strong promoter (PGK1), while disrupting the gene coding alcohol dehydrogenase (ADH2). The highest glucoamylase activity for TQ1 was 93.26 U/ml compared with host strain T1 (12.36 U/ml) and wild-type industrial yeast strain YSF5 (10.39 U/ml), respectively. European Brewery Convention (EBC) tube fermentation tests comparing the fermentation broths of TQ1 with T1 and YSF5 showed that the real extracts were reduced by 15.79% and 22.47%; the main residual maltotriose concentrations were reduced by 13.75% and 18.82%; the caloric contents were reduced by 27.18 and 35.39 calories per 12 oz. Owing to the disruption of the ADH2 gene in TQ1, the off-flavor acetaldehyde concentrations in the fermentation broth were 9.43% and 13.28%, respectively, lower than that of T1 and YSF5. No heterologous DNA sequences or drug resistance genes were introduced into TQ1. Hence, the gene manipulations in this work properly solved the addressed problems in commercial beer manufacture.