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==Review of Scientific Analysis==
The published analysis of beer that is co-fermented with ''S. cerevisiae'' and ''Brettanomyces'' is rare. In this section, published data on this topic will be reviewed.
Nick Mader of Fremont Brewing (2017 Master Brewers Conference Presentation) compared various flavor compounds produced between a 100% ''S. cerevisiae'' (BSI-565, Wallionian Saison yeast) and 100% ''B. bruxellensis'' (BSI-Drei), and combinations of 75%/25%, 50%/50%, and 25%/75% inoculations of the BSI-565 strain and BSI-Drei strain. Fermentations were completed in 35 days, and the beers were analyzed for their ester and phenol content. Attenuation results were about the same for the 100% BSI-565 and the co-fermentation of BSI-565 and BSI-Drei, while the attenuation rate was around 12% lower for the 100% BSI-Drei fermentation, indicating that co-fermentation with these two particular strains did not greatly affect attenuation and that the BSI-Drei did not ferment as well by itself.
The esters that were analyzed were ethyl acetate, ethyl butyrate, ethyl hexanoate, ethyl decanoate, ethyl octanoate, isoamyl acetate, isobutyl alcohol, and isoamyl alcohol. Ethyl acetate was highest in the 100% BSI-565 fermentation (43 ppm; above the 33 ppm odor threshold), and lowest in the 100% BSI-Drei fermentation (21 ppm; below the 33 ppm odor threshold). The different co-fermentation rates formed a pattern of more ethyl acetate as the pitching rate of BSI-Drei was increased, but they were still lower than the 100% BSI-565 fermentation. The 75/25 ratio produced 27 ppm, 50/50 produced 34 ppm, and the 25/75 produced 42 ppm (BSI-565 to BSI-Drei ratio in percent pitching rate). Ethyl butyrate was highest in the 100% BSI-565, and curved downward as the pitching rate for the BSI-565 strain was decreased. Ethyl butyrate was below odor threshold in the 100% BSI-Drei fermentation. This indicates that the production of ethyl butyrate was dependent on the pitching rate of BSI-565, and that the BSI-Drei strain did not produce significant amounts of this ester. For each of the esters ethyl hexanoate, ethyl decanoate, ethyl octanoate, they had a slight decrease as the pitching rate of BSI-565 decreased, indicating that these esters are produced more by the BSI-565 strain, however the small measured differences may not be reflected in the actual taste/aroma of the beers since the differences were so small. The exception was ethyl decanoate which was around 3x higher in the 100% BSI-Drei, which indicates that ethyl decanoate is a major flavor contributor to 100% BSI-Drei fermentations. Isoamyl acetate, which was above odor threshold in the 100% BSI-565 fermentation, was almost not detectable in any of the fermentations that contained BSI-Drei (it was 0 ppm in the 100% BSI-Drei fermentation), which is in agreement with other studies that ''Brettanomyces'' hydrolyzes this ester. The alcohols isobutyl alcohol and isoamyl alcohol were slightly decreased as the pitching rate of BSI-565 decreased, and were extremely low in the 100% BSI-Drei, indicating that these alcohols were produced more so by BSI-565.
The phenols that were measured in Mader's experiment were 4-vinylguaiacol (clove), 4-ethylguaiacol (smokey, spicy), and 4-ethylphenol (medicinal, barnyard). While the 100% BSI-565 fermentation had high levels of 4-VG (1800 ppm), they were less than half the amount in the co-fermented ferments (600-800 ppm) but still above odor threshold (300 ppm) (the different ratios of BSI-565 to BSI-Drei did not have a large impact), and 4-VG was below threshold in the 100% BSI-Drei fermentation. 4-EG and 4-EP had high levels in the co-fermentations with BSI-565 and BSI-Drei and the 100% BSI-Drei, and the ratios did not have a large impact. This is in agreement with another experiment by [[Brettanomyces_secondary_fermentation_experiment|Lance Shaner and Richard Preiss]] that showed that pitching rate of ''Brettanomyces'' after fermentation with ''S. cerevisiae'' did not have a great affect on the levels of phenols produced.
==See Also==
==References==
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[[Category:Techniques]]