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Nonconventional Yeasts and Bacteria

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update XXX (missing). thanks, Cook
Many other strains have a lower fermentation capacity. Because of this, studies in wine have focused on co-fermentation with ''Saccharomyces'' in order to reduce the pH of the wine and provide fruity ethyl lacate esters. Three strains were tested by Dimizio et al. (2016) for their fermentation characteristics after 21 days of fermentation under different conditions. They found that all three strains fermented maltose at similar levels of ''S. cerevisiae'', but none fermented maltotriose and other studies have tested strains that do not ferment maltose. The ''L. thermotolerans'' strains produced 6-12% less total ethanol than ''S. cerevisiae'', showing that in general that this species has lower attenuation than brewers yeast. All three strains of ''L. thermotolerans'' produced lactic acid, but it took 21 days to achieve maximum lactic acid levels, and only one strain resulted in beers that were at a pH of 3.77 (the other strains produced beers that were at a pH of 4.11 and 4.28, which were similar to the ''S. cerevisiae'' strain that was tested). It was noted that other strains have been reported to produce a pH of 3.6, so the ability of ''L. thermotolerans'' to sour beer is widely dependent on strain. ''L. thermotolerans'' also produced significantly more glycerol than the beer yeast (between 65-75% more at day 21), which demonstrates that this species could be used to improve mouthfeel. Pitching rate didn't greatly affect the amount of lactic acid produced, although the lowest pitching rate tested produced slightly more lactic acid. Repitching up to five generations did not seem to have a great effect on viability and slightly improved its fermentation capability, and they were not noticeably affected by high IBU's (60) or low vs high oxygenation levels. ''L. thermotolerans'' did not have a negative effect on head retention, and behaved similarly to ''S. cerevisiae'' as far as flocculation. Overall, the levels of VDK's and diacetyl were lower than that of the tested strain of ''S. cerevisiae'', however, another study showed that they were higher in wort that was highly saturated with oxygen. The sensory effects of ''L. thermotolerans'' were described as "positive", but the data was not shown in the study. At lower fermentation temperatures (16°C), the tasters described the beer as tasting "fruity, floral, sour, clove, melon, and strawberry". However, in another study of another strain that did not ferment well was described as "yielded strong, unpleasant phenolic aromas, notably 4-ethylphenol." This seems to indicate that ''L. thermotolerans'' generally produces phenols, although phenols were not measured in this study. One strain tested was shown to have higher beta-glucosidase activity, which could indicate that it could aid in the break down [[Glycosides]] in hops or fruit <ref name="Domizio_2016" />.
A study by [https://www.nature.com/articles/s41598-018-33105-7 Hranilovic et al. (2018)] looked at the fermentation profile of 94 strains of ''L. thermotolerans'' from all over the world in Chardonnay grape juice. They found a wider range of fermentation profiles for different strains of this species. They achieved a range of 7.3 to 10.6% ABV, preferring glucose over fructose. Some strains produced extreme levels of glycerol (8.0 g/L) while others produced moderate amounts. 48 of the strains produced more lactic acid than they did glycerol, which is a significant amount of lactic acid, the highest produced being XXX(missing) 12 g/L. Some strains didn't produce nearly as much lactic acid though, producing as little as 1.8 g/L. Acetic acid production was insignificant in all strains tested, but they all produced low levels. They found that a wide range of secondary metabolites were produced, including high alcohols (hexanol, phenylethanol, methylbenzenemethanol, isobutanol, isoamyl alcohol, methyl-butanol, methyl-pentanol, ethylhexanol, butanol, nonanol, octanol, and decanol). Some strains produced high levels of hexanol and octanol. Many esters were produced as well, including ethyl propanoate, ethyl octanoate, ethyl decanoate, ethyl 9-decenoate, diethyl succinate, ethyl acetate, isobutyl acetate, isoamyl acetate, 2-phenylethyl acetate, and amyl lactate. Other aromatic compounds were also produced, including aldehydes, ketones, and the terpene citronellol. They found that some groups of strains produced some compounds more than others, indicating a potentially high degree of variability on the flavors produced by different strains of ''L. thermotolerans'' <ref>[https://www.nature.com/articles/s41598-018-33105-7 Ana Hranilovic, Joanna M. Gambetta, Leigh Schmidtke, Paul K. Boss, Paul R. Grbin, Isabelle Masneuf-Pomarede, Marina Bely, Warren Albertin & Vladimir Jiranek. 2018.]</ref>.
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