Editing Yeast
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The beer filtration process reduces the contents of antioxidant phenolic compounds and melanoidins and the AOX of wort. During the cooling stage, the spontaneous adsorption of phenolic compounds and melanoidins on wort dregs and the polymerization and precipitation of catechins and epicatechins lead to the decrease of TPC in beer (Ruiz- Ruiz, Del Carmen Esapadas Aldana, Cruz, & Segura-Campos, 2020). With the increase of diatomite consumption, a large concentration of iron ions is introduced, which decreases the DPPH scavenging rate, because transition ions such as iron and copper play an important cat alytic role in the Fenton reaction, producing hydroxyl free radicals with high activity and reducing the oxidation resistance of beer (Jurková et al., 2012; Pascoe, Ames, & Chandra, 2003). The addition of tannins has an obvious effect on the rate of scavenging of DPPH free radicals, indicating that the addition of tannins will help to chelate iron ions and reduce the effect of iron ions in diatomite on beer. The reducing power of beer can be improved by maintaining pH within the range 4.3–4.4 (Han, 2016). After cooling and filtration, 6% of selenium is lost from the level in raw materials, and the total loss of selenium over the whole process of beer fermentation is 94% (Rodrigo et al., 2015). It can be seen that the percentage selenium loss is quite high, which deserves attention.<ref name=yangao/> | The beer filtration process reduces the contents of antioxidant phenolic compounds and melanoidins and the AOX of wort. During the cooling stage, the spontaneous adsorption of phenolic compounds and melanoidins on wort dregs and the polymerization and precipitation of catechins and epicatechins lead to the decrease of TPC in beer (Ruiz- Ruiz, Del Carmen Esapadas Aldana, Cruz, & Segura-Campos, 2020). With the increase of diatomite consumption, a large concentration of iron ions is introduced, which decreases the DPPH scavenging rate, because transition ions such as iron and copper play an important cat alytic role in the Fenton reaction, producing hydroxyl free radicals with high activity and reducing the oxidation resistance of beer (Jurková et al., 2012; Pascoe, Ames, & Chandra, 2003). The addition of tannins has an obvious effect on the rate of scavenging of DPPH free radicals, indicating that the addition of tannins will help to chelate iron ions and reduce the effect of iron ions in diatomite on beer. The reducing power of beer can be improved by maintaining pH within the range 4.3–4.4 (Han, 2016). After cooling and filtration, 6% of selenium is lost from the level in raw materials, and the total loss of selenium over the whole process of beer fermentation is 94% (Rodrigo et al., 2015). It can be seen that the percentage selenium loss is quite high, which deserves attention.<ref name=yangao/> | ||
SafaleTM S-04 is a maltotriose negative yeast, thus sugars remain into the beer contributing to sweet character to aroma and taste.<ref name=ligdef>Liguori L, De Francesco G, Orilio P, Perretti G, Albanese D. [https://link.springer.com/article/10.1007/s13197-020-04740-8 Influence of malt composition on the quality of a top fermented beer.] ''J Food Sci Technol.'' 2021;58:2295–2303.</ref> | SafaleTM S-04 is a maltotriose negative yeast, thus sugars remain into the beer contributing to sweet character to aroma and taste.<ref name=ligdef>Liguori L, De Francesco G, Orilio P, Perretti G, Albanese D. [https://link.springer.com/article/10.1007/s13197-020-04740-8 Influence of malt composition on the quality of a top fermented beer.] ''J Food Sci Technol.'' 2021;58:2295–2303.</ref> | ||
Yeast is regarded as the best "antioxidant" for brewing due to its strong ability to absorb dissolved oxygen.<ref name=niecon>Nielsen H. [https://onlinelibrary.wiley.com/doi/pdf/10.1002/j.2050-0416.1973.tb03517.x The control of oxygen in beer processing.] ''J Inst Brew.'' 1973;79(2):147–154.</ref> | Yeast is regarded as the best "antioxidant" for brewing due to its strong ability to absorb dissolved oxygen.<ref name=niecon>Nielsen H. [https://onlinelibrary.wiley.com/doi/pdf/10.1002/j.2050-0416.1973.tb03517.x The control of oxygen in beer processing.] ''J Inst Brew.'' 1973;79(2):147–154.</ref> | ||
Although sufficient oxygen must be supplied to yeast to promote lipid synthesis and satisfactory fermentation, it has been demonstrated that oxygen can lower the viability of yeast, exerting its effect via superoxide or species derived from it (20). Upon exposure to oxygen, yeast responds by synthesizing SOD and catalase, enzymes that are suppressed under anaerobic conditions (20). As for all aerobic organisms, those enzymes are triggered to promote protection against radical damages. In the transition period necessary for the elaboration of these enzymes, yeast is susceptible to oxygen radicals, a problem that should be considered when designing systems for providing oxygen to yeast.<ref name=bammul>Bamforth CW, Muller RE, Walker MD. [https://www.tandfonline.com/doi/abs/10.1094/ASBCJ-51-0079 Oxygen and oxygen radicals in malting and brewing: a review.] ''J Am Soc Brew Chem.'' 1993;51(3):79–88.</ref> | Although sufficient oxygen must be supplied to yeast to promote lipid synthesis and satisfactory fermentation, it has been demonstrated that oxygen can lower the viability of yeast, exerting its effect via superoxide or species derived from it (20). Upon exposure to oxygen, yeast responds by synthesizing SOD and catalase, enzymes that are suppressed under anaerobic conditions (20). As for all aerobic organisms, those enzymes are triggered to promote protection against radical damages. In the transition period necessary for the elaboration of these enzymes, yeast is susceptible to oxygen radicals, a problem that should be considered when designing systems for providing oxygen to yeast.<ref name=bammul>Bamforth CW, Muller RE, Walker MD. [https://www.tandfonline.com/doi/abs/10.1094/ASBCJ-51-0079 Oxygen and oxygen radicals in malting and brewing: a review.] ''J Am Soc Brew Chem.'' 1993;51(3):79–88.</ref> | ||
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Starters for liquid yeast | Starters for liquid yeast | ||
Yeast produce membrane lipids only when grown aerobically. In the initial growth phase, proper oxygen management leads to proper production and storage of sterols in the yeast cell, which can be shared with subsequent daughter cells. It is possible to increase yeast ethanol tolerance by promoting synthesis of sterols, by adding oxygen (air) in the starter and during fermentation. Yeast lees deplete the oxygen content and can impact the redox potential and formation of VSCs.<ref name="Zoecklein">Zoecklein B. [https://www. | Yeast produce membrane lipids only when grown aerobically. In the initial growth phase, proper oxygen management leads to proper production and storage of sterols in the yeast cell, which can be shared with subsequent daughter cells. It is possible to increase yeast ethanol tolerance by promoting synthesis of sterols, by adding oxygen (air) in the starter and during fermentation. Yeast lees deplete the oxygen content and can impact the redox potential and formation of VSCs.<ref name="Zoecklein">Zoecklein B. [https://www.apps.fst.vt.edu/extension/enology/EN/133.html Enology notes #133.] Wine/Enology Grape Chemistry Group at Virginia Tech. Published 2007. Accessed 2020.</ref> | ||
While oxidative stress is known to occur, is it significantly less that stress from carbon dioxide. High amounts of foam means that insufficient oxygen delivery is occurring.<ref>https://www.mbaa.com/publications/tq/tqPastIssues/2005/Abstracts/TQ-42-0128.htm</ref> | While oxidative stress is known to occur, is it significantly less that stress from carbon dioxide. High amounts of foam means that insufficient oxygen delivery is occurring.<ref>https://www.mbaa.com/publications/tq/tqPastIssues/2005/Abstracts/TQ-42-0128.htm</ref> | ||
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*https://www.homebrewtalk.com/threads/the-ideal-starter-transcript-of-an-article-on-braumagazin-de.679661/ | *https://www.homebrewtalk.com/threads/the-ideal-starter-transcript-of-an-article-on-braumagazin-de.679661/ | ||
Biomass may actually be more important that cell count with regard to pitch rate.<ref>[https:// | Biomass may actually be more important that cell count with regard to pitch rate.<ref>[https://www.milkthefunk.live/podcast/2019/12/6/wiki-kwiki-005-lance-shaner-of-omega-yeast-labs "Wiki Kwiki #005 - Lance Shaner of Omega Yeast Labs"] (at ~30 minutes) Milk the Funk podcast, December 2019.</ref> However this isn't easy to measure at home. Pitching rate calculators are still useful for determining correct pitch rate. | ||
Yeast in worts rich in glucose may not be able to adapt to metabolize maltose and maltotriose, leading to slow or stuck fermentations.<ref name=bsp>Briggs DE, Boulton CA, Brookes PA, Stevens R. [[Library|''Brewing Science and Practice.'']] Woodhead Publishing Limited and CRC Press LLC; 2004.</ref> | Yeast in worts rich in glucose may not be able to adapt to metabolize maltose and maltotriose, leading to slow or stuck fermentations.<ref name=bsp>Briggs DE, Boulton CA, Brookes PA, Stevens R. [[Library|''Brewing Science and Practice.'']] Woodhead Publishing Limited and CRC Press LLC; 2004.</ref> | ||
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Nitrogen is generally plentiful in wort and typically does not require supplementation for beer production.<ref name="Ferreira"/><ref name=jonesbudde>Jones BL, Budde AD. [https://www.sciencedirect.com/science/article/abs/pii/S0733521004001067 How various malt endoproteinase classes affect wort soluble protein levels.] ''J Cereal Sci.'' 2005;41(1):95–106.</ref> The concentration of the amino acids isoleucine, valine, phenylalanine, glycine, alanine, tyrosine, lysine, histidine, arginine and leucine, are considered important, as these are an important part of the complex system regulating the biosynthesis of flavour-active compounds formed by yeast.<ref name="Ferreira"/> However, if supplementation is desired, a mixture of amino acids is more favorable to growth than when ammonium ions are the source of nitrogen.<ref name="Ferreira"/> Phenolic yeast may have a higher nitrogen requirement.<ref name="Ferreira"/> | Nitrogen is generally plentiful in wort and typically does not require supplementation for beer production.<ref name="Ferreira"/><ref name=jonesbudde>Jones BL, Budde AD. [https://www.sciencedirect.com/science/article/abs/pii/S0733521004001067 How various malt endoproteinase classes affect wort soluble protein levels.] ''J Cereal Sci.'' 2005;41(1):95–106.</ref> The concentration of the amino acids isoleucine, valine, phenylalanine, glycine, alanine, tyrosine, lysine, histidine, arginine and leucine, are considered important, as these are an important part of the complex system regulating the biosynthesis of flavour-active compounds formed by yeast.<ref name="Ferreira"/> However, if supplementation is desired, a mixture of amino acids is more favorable to growth than when ammonium ions are the source of nitrogen.<ref name="Ferreira"/> Phenolic yeast may have a higher nitrogen requirement.<ref name="Ferreira"/> | ||
Yeast consume at least 100-140ppm FAN in wort. Since proline cannot be utilized, wort has to contain 200-220ppm FAN. Inadequate nutrition can result in reduced yeast propagation and a delay in fermentation and maturation, and ultimately the retention of undesirable "young beer" off-flavors. Higher modified malts produce more FAN.<ref>Kunze, Wolfgang. "3.2 Mashing." ''Technology Brewing & Malting.'' Edited by Olaf Hendel, 6th English Edition ed., | Yeast consume at least 100-140ppm FAN in wort. Since proline cannot be utilized, wort has to contain 200-220ppm FAN. Inadequate nutrition can result in reduced yeast propagation and a delay in fermentation and maturation, and ultimately the retention of undesirable "young beer" off-flavors. Higher modified malts produce more FAN.<ref>Kunze, Wolfgang. "3.2 Mashing." ''Technology Brewing & Malting.'' Edited by Olaf Hendel, 6th English Edition ed., VBL Berlin, 2019, p. 230.</ref> If [[adjuncts]] are used, the brewer should consider using a protein rest (45-50°C) (see [[Mashing]]) or adding yeast nutrient. | ||
Worts that are prepared with reasonable percentages of malt tend to be rich in amino acids. Low FAN levels are undesirable in wort. The traditional rule is that serious problems (long lags, high diacetyl, etc) can result from FAN below 150-175ppm. A 12°P malt wort will typically have 225-275ppm FAN, which is ideal.<ref name=fix>Fix, George. ''Principles of Brewing Science.'' 2nd ed., Brewers Publications, 1999.</ref> As a general rule, it is usually desirable to keep FAN levels below 350ppm, something that can be achieved with a suitable [[mashing]] schedule. | Worts that are prepared with reasonable percentages of malt tend to be rich in amino acids. Low FAN levels are undesirable in wort. The traditional rule is that serious problems (long lags, high diacetyl, etc) can result from FAN below 150-175ppm. A 12°P malt wort will typically have 225-275ppm FAN, which is ideal.<ref name=fix>Fix, George. ''Principles of Brewing Science.'' 2nd ed., Brewers Publications, 1999.</ref> As a general rule, it is usually desirable to keep FAN levels below 350ppm, something that can be achieved with a suitable [[mashing]] schedule. | ||
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In many breweries producing South- | In many breweries producing South- | ||
ern German-style wheat beer, otherwise known as weissbier, after the installation of new cylindroconical fermentors, it is common for the beers to exhibit a noticeable decline in the bouquet characteristic of the style, which consists of primarily of compounds like isoamyl acetate (banana ester)[2]. The reason behind this somewhat diminished weissbier aroma is, among others, the high rate of yeast reproduction, which reduces the amount of the acetyl-coenzyme A available for ester formation. In addition, the high hydrostatic pressure in vertical vessels moderates the production of higher alcohols, thus reducing the numbers of reactants for the formation of esters. In short, the higher the liquid level is in a fermentation tank, the stronger the convection and homogenization, which results in a reduction in the formation of esters (fig. 4).<ref name=sacher2>Sacher B, Becker T, Narziss L. [http://www. | ern German-style wheat beer, otherwise known as weissbier, after the installation of new cylindroconical fermentors, it is common for the beers to exhibit a noticeable decline in the bouquet characteristic of the style, which consists of primarily of compounds like isoamyl acetate (banana ester)[2]. The reason behind this somewhat diminished weissbier aroma is, among others, the high rate of yeast reproduction, which reduces the amount of the acetyl-coenzyme A available for ester formation. In addition, the high hydrostatic pressure in vertical vessels moderates the production of higher alcohols, thus reducing the numbers of reactants for the formation of esters. In short, the higher the liquid level is in a fermentation tank, the stronger the convection and homogenization, which results in a reduction in the formation of esters (fig. 4).<ref name=sacher2>Sacher B, Becker T, Narziss L. [http://www.lowoxygenbrewing.com/wp-content/uploads/2017/04/pddvxvf.pdf Some reflections on mashing – Part 2.] ''Brauwelt International.'' 2016;6:392-397.</ref> | ||
The estery notes in beer have been observed to become more pronounced as the ratio of glucose to maltose tips in favor of glucose.<ref name=sacher2/> Alcoholic fermentation with yeast in the presence of high concentrations of glucose leads to a delay in the onset of maltose metabolism after an initial rapid decline in the extract content of the wort (similar to a "second lag phase"). This explains the plateau in the extract curve. During this time, the yeast are scarcely reproducing and are compensating with the synthesis of maltose permease and maltase. The diminished yeast reproduction results in overflow of the acetyl-CoA pool and thus greater ester formation and fruitier beers. | The estery notes in beer have been observed to become more pronounced as the ratio of glucose to maltose tips in favor of glucose.<ref name=sacher2/> Alcoholic fermentation with yeast in the presence of high concentrations of glucose leads to a delay in the onset of maltose metabolism after an initial rapid decline in the extract content of the wort (similar to a "second lag phase"). This explains the plateau in the extract curve. During this time, the yeast are scarcely reproducing and are compensating with the synthesis of maltose permease and maltase. The diminished yeast reproduction results in overflow of the acetyl-CoA pool and thus greater ester formation and fruitier beers. | ||
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This also comes into play when using [[adjuncts]] in brewing. | This also comes into play when using [[adjuncts]] in brewing. | ||
[[File:Flavor-compound-production.png | [[File:Flavor-compound-production.png]] | ||
In many Belgian-style specialty beers, POF+ S. cerevisiae strains are required to impart spice notes in the finished beer.<ref name=len>Lentz M. [https://www.mdpi.com/2311-5637/4/1/20 The impact of simple phenolic compounds on beer aroma and flavor.] ''Fermentation.'' 2018;4(1):20.</ref> There is a wide variety among these strains regarding POF activity. This at least partially explains the difference in volatile flavor compounds (phenolics and esters) produced by different strains such as those utilized for [[weissbier]] vs [[Belgian tripel]] styles for example. | In many Belgian-style specialty beers, POF+ S. cerevisiae strains are required to impart spice notes in the finished beer.<ref name=len>Lentz M. [https://www.mdpi.com/2311-5637/4/1/20 The impact of simple phenolic compounds on beer aroma and flavor.] ''Fermentation.'' 2018;4(1):20.</ref> There is a wide variety among these strains regarding POF activity. This at least partially explains the difference in volatile flavor compounds (phenolics and esters) produced by different strains such as those utilized for [[weissbier]] vs [[Belgian tripel]] styles for example. | ||
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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/> | 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 == | == Articles to be reviewed == | ||
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*Verbelen, P. J., and Delvaux, F. R. Brewing yeast in action: Beer fermentation. In: Applied Microbiology. M. K. Rai and P. D. Bridge, Eds. CAB International, Oxon, UK. Pp. 110-135, 2009. | *Verbelen, P. J., and Delvaux, F. R. Brewing yeast in action: Beer fermentation. In: Applied Microbiology. M. K. Rai and P. D. Bridge, Eds. CAB International, Oxon, UK. Pp. 110-135, 2009. | ||
*[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5620630/ Microorganisms in Fermented Apple Beverages: Current Knowledge and Future Directions] | *[https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5620630/ Microorganisms in Fermented Apple Beverages: Current Knowledge and Future Directions] | ||
*[http://www. | *[http://www.lowoxygenbrewing.com/wp-content/uploads/2017/04/fischer_0606.pdf Effects of hydrostatic high pressure on microbiological and technological characteristics of beer] | ||
*http://www. | *http://www.lowoxygenbrewing.com/wp-content/uploads/2017/04/poeschl_0807.pdf The Influence of Fermentation-Control on the Colloidal Stability and the Reducing Power of the Resulting Bottom Fermented Beers | ||
*Krogerus, K. and Gibson, B.: A re-evaluation of diastatic Saccharomyces cerevisiae strains and their role in brewing. Applied Microbiology and Biotechnology, 104 (2020), pp. 3745-3756. | *Krogerus, K. and Gibson, B.: A re-evaluation of diastatic Saccharomyces cerevisiae strains and their role in brewing. Applied Microbiology and Biotechnology, 104 (2020), pp. 3745-3756. | ||
*https://www.biorxiv.org/content/10.1101/2020.06.26.166157v1.full | *https://www.biorxiv.org/content/10.1101/2020.06.26.166157v1.full | ||
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*[https://www.sciencedirect.com/science/article/abs/pii/0922338X9290137J "Effect of pitching yeast and wort preparation on flavor stability of beer"] | *[https://www.sciencedirect.com/science/article/abs/pii/0922338X9290137J "Effect of pitching yeast and wort preparation on flavor stability of beer"] | ||
*[https://pubs.acs.org/doi/abs/10.1021/jf9037387 Decrease of Aged Beer Aroma by the Reducing Activity of Brewing Yeast] | *[https://pubs.acs.org/doi/abs/10.1021/jf9037387 Decrease of Aged Beer Aroma by the Reducing Activity of Brewing Yeast] | ||
== References == | == References == |