Yeast: Difference between revisions

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yeast strains significantly affected the antioxidant level of beer. The antioxidant value of beer with yeast strain C was higher than that of the other two strains and its flavor stability was the best among these three beers. It was very interesting that there was no correlation between the fermentation time and the antioxidant level. Sulfite content in beer is also shown in Table II. The results show that the effect of yeast strain on beer flavor stability is mainly due to the ability of yeast to produce sulfite. These results suggest that the selection of yeast strain is one of the important factors for improvement of beer flavor stability. Similar suggestions have been also made previously by Narziss et al (13).<ref name=uchono>Uchida M, Ono M. [https://www.tandfonline.com/doi/abs/10.1094/ASBCJ-58-0008 Technological approach to improve beer flavor stability: analysis of the effect of brewing processes on beer flavor stability by the electron spin resonance method.] ''J Am Soc Brew Chem.'' 2000;58(1):8–13.</ref>

Pitching rates also had an effect on the EA (endogenous antioxidant) value of finished beer (Table IV). The EA value of beer increased with pitching rates, while the fermentation time significantly decreased. In the case of 54 × 106 cells/ml, the EA value of beer significantly increased, but the profile of volatile compounds in beer was rather different from the others (data not shown). In the range of pitching rates conventionally used, the effect of pitching rates on the EA value of beer was considered not great. The sulfite content in beer slightly increased with pitching rates. The effect of pitching rates on the EA value might be caused partly by the differences in the sulfite content of beer, although the EA value was not necessarily in proportion to the sulfite contents. Fermentation temperature had an effect on the EA value of finished beer (Table V). Fermentation temperatures of 9, 12, and 15°C were tested. The EA value of these beers was almost the same, although the fermentation time was significantly decreased with the rise in temperature. Although the data is not shown here, in the case of beer brewed with another yeast strain, a different result was observed: The EA value of beer brewed at a low fermentation temperature had the tendency of having higher sulfite content and higher EA value than those of the beer brewed at a high temperature. The reports on temperature dependency of sulfite production during fermentation were different among some researchers (2,15,19). It seemed that the effect of fermentation temperature on sulfite production might be different based on the physiology of the yeast strains used. Thus, the effect of fermentation temperature on beer flavor stability seemed to be different among the yeast strains used. Lustig et al, on the other hand, reported that higher temperature during the primary fermentation might be harmful from the view of residual concentration of some aging aldehydes (11). These results suggested that the selection of fermentation temperature for improving beer flavor stability must also be made after careful consideration. To clarify where there is a simple relationship between EA value and sulfite concentration of beer, or not, the plot of EA values against sulfite concentration is shown using the data from these various fermentation experiments (Fig. 4). These results show that sulfite is one of the essential and important determinants (antioxidants) of EA value, but other factors may also influence EA value.<ref name=uchono/>

== Articles to be reviewed ==