Selection of Saccharomyces pastorianus variants with improved fermentation performance under very high gravity wort conditions

In this study, the 30oBx wort with 30% maltose syrup adjunct was used for very high gravity brewing. Increase in pitching rate from 25×106 cells/mL to 125×106 cells/mL shortened the primary fermentation time and augmented the level of ethanol and diacetyl in the green beer. The suitable pitching rate was 75×106 cells/mL. Under this condition, the fermentation time reduced 44.2% and the ethanol concentration in the green beer increased 13.7% in comparison with those in the culture with conventional pitching rate; the ethanol yield achieved maximum of 44.1%. Combination of high pitching rate and nutritional supplementation to 30oBx wort reduced the fermentation time 8.7% and maintained the similar ethanol content in the green beer and the similar ethanol yield in comparison with the high pitching rate culture.

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Selection from Industrial Lager Yeast Strains of Variants with Improved Fermentation Performance in Very-High-Gravity Worts

Applied and Environmental Microbiology ◽

10.1128/aem.03153-09 ◽

2010 ◽

Vol 76 (5) ◽

pp. 1563-1573 ◽

Cited By ~ 43

Author(s):

Anne Huuskonen ◽

Tuomas Markkula ◽

Virve Vidgren ◽

Luis Lima ◽

Linda Mulder ◽

...

Keyword(s):

Survival Rates ◽

High Gravity ◽

Fermentation Performance ◽

Lager Yeast ◽

Very High Gravity ◽

Sedimentation Behavior ◽

Yeast Strains ◽

Industrial Strains ◽

Improved Performance ◽

Very High

ABSTRACT There are economic and other advantages if the fermentable sugar concentration in industrial brewery fermentations can be increased from that of currently used high-gravity (ca. 14 to 17ï¿½P [degrees Plato]) worts into the very-high-gravity (VHG; 18 to 25ï¿½P) range. Many industrial strains of brewer's yeast perform poorly in VHG worts, exhibiting decreased growth, slow and incomplete fermentations, and low viability of the yeast cropped for recycling into subsequent fermentations. A new and efficient method for selecting variant cells with improved performance in VHG worts is described. In this new method, mutagenized industrial yeast was put through a VHG wort fermentation and then incubated anaerobically in the resulting beer while maintaining the α-glucoside concentration at about 10 to 20 gï¿½liter−1 by slowly feeding the yeast maltose or maltotriose until most of the cells had died. When survival rates fell to 1 to 10 cells per 106 original cells, a high proportion (up to 30%) of survivors fermented VHG worts 10 to 30% faster and more completely (residual sugars lower by 2 to 8 gï¿½liter−1) than the parent strains, but the sedimentation behavior and profiles of yeast-derived flavor compounds of the survivors were similar to those of the parent strains.

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Isolation and Characterization of Brewer's Yeast Variants with Improved Fermentation Performance under High-Gravity Conditions

Applied and Environmental Microbiology ◽

10.1128/aem.02109-06 ◽

2006 ◽

Vol 73 (3) ◽

pp. 815-824 ◽

Cited By ~ 81

Author(s):

Lies Blieck ◽

Geert Toye ◽

Franï¿½oise Dumortier ◽

Kevin J. Verstrepen ◽

Freddy R. Delvaux ◽

...

Keyword(s):

Pilot Scale ◽

Superior Performance ◽

High Gravity ◽

Brewer’S Yeast ◽

Fermentation Performance ◽

Altered Expression ◽

Brewer's Yeast ◽

Very High Gravity ◽

Isolation And Characterization ◽

Saccharomyces Pastorianus

ABSTRACT To save energy, space, and time, today's breweries make use of high-gravity brewing in which concentrated medium (wort) is fermented, resulting in a product with higher ethanol content. After fermentation, the product is diluted to obtain beer with the desired alcohol content. While economically desirable, the use of wort with an even higher sugar concentration is limited by the inability of brewer's yeast (Saccharomyces pastorianus) to efficiently ferment such concentrated medium. Here, we describe a successful strategy to obtain yeast variants with significantly improved fermentation capacity under high-gravity conditions. We isolated better-performing variants of the industrial lager strain CMBS33 by subjecting a pool of UV-induced variants to consecutive rounds of fermentation in very-high-gravity wort (>22ï¿½ Plato). Two variants (GT336 and GT344) showing faster fermentation rates and/or more-complete attenuation as well as improved viability under high ethanol conditions were identified. The variants displayed the same advantages in a pilot-scale stirred fermenter under high-gravity conditions at 11ï¿½C. Microarray analysis identified several genes whose altered expression may be responsible for the superior performance of the variants. The role of some of these candidate genes was confirmed by genetic transformation. Our study shows that proper selection conditions allow the isolation of variants of commercial brewer's yeast with superior fermentation characteristics. Moreover, it is the first study to identify genes that affect fermentation performance under high-gravity conditions. The results are of interest to the beer and bioethanol industries, where the use of more-concentrated medium is economically advantageous.

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