Kvasný průmysl (May 2004)
Wort sugars uptake rate and cell cycle of brewing yeast. I. Wort sugars metabolism of three brewing yeast strains during pilot plant fermentation.
Abstract
The objective of this work was to study the metabolic activity of three strains of lager yeast in relation to the utilization of main wort sugars glucose, maltose and fructose. Yeast strains No. 2, 7 and 95 (marked in accordance with RIBM 655 - Culture Collection of Brewing Yeasts) were used in the study. The experiments were carried out in pilot plant scale fermenter at the temperature of 13 °C. The original gravity of wort was 12 % and the malt in grist was partly substituted by unmalted barley. During pilot plant fermentation the wort sugars were utilized step by step. Glucose was utilized first followed by fructose and maltose. Maltose was fermented after the glucose concentration in wort decreased to 35-55.7 % of its original level. Strains No. 2 and 95 seemed to be less sensitive to glucose since the exponential phase of maltose utilization started at 45 % (strain No. 2) and 55.7 % (strain No. 95) of residual glucose level in wort, which is more than the concentrations found in the literature. Comparing the fermentable sugar uptake rates there were found differences between by the studied strains. The strain No. 7 showed the shortest and fastest linear phase maltose utilization. The linear phase of maltose utilization was the longest for the strain No. 95 while the properties of the strain No. 2 could be found between strains No. 7 and 95. During pilot plant main fermentation changes in wort sugars ratio occurred and it was proved that fructose is fermented at lower rate and to lower degree than glucose and maltose. There were observed differences among examined strains in terms of changes of the wort sugars ratio, however, not all the changes were statistically significant. Fructose seems to play a significant role in the changes of the "sweetness character" between unfermented malt and beer.The objective of this work was to study the metabolic activity of three strains of lager yeast in relation to the utilization of main wort sugars glucose, maltose and fructose. Yeast strains No. 2, 7 and 95 (marked in accordance with RIBM 655 - Culture Collection of Brewing Yeasts) were used in the study. The experiments were carried out in pilot plant scale fermenter at the temperature of 13 °C. The original gravity of wort was 12 % and the malt in grist was partly substituted by unmalted barley. During pilot plant fermentation the wort sugars were utilized step by step. Glucose was utilized first followed by fructose and maltose. Maltose was fermented after the glucose concentration in wort decreased to 35-55.7 % of its original level. Strains No. 2 and 95 seemed to be less sensitive to glucose since the exponential phase of maltose utilization started at 45 % (strain No. 2) and 55.7 % (strain No. 95) of residual glucose level in wort, which is more than the concentrations found in the literature. Comparing the fermentable sugar uptake rates there were found differences between by the studied strains. The strain No. 7 showed the shortest and fastest linear phase maltose utilization. The linear phase of maltose utilization was the longest for the strain No. 95 while the properties of the strain No. 2 could be found between strains No. 7 and 95. During pilot plant main fermentation changes in wort sugars ratio occurred and it was proved that fructose is fermented at lower rate a
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