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611
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Changes
→Brettanomyces dominance
Brettanomyces inherits the role of most prominent yeast genera from Saccharomyces around 8 months, and continues consuming sugars in the wort. Final attenuation can reach over 80% in lambic through the continued action of Brettanomyces, which is often referred to as "overattenuation" or "superattenuation". This is greater than is usually possible with Saccharomyces alone, as Brettanomyces is able to metabolise sugars that Saccharomyces cannot, generally known as "dextrins". In addition, brettanomyces can metabolise laminarin and pectin, and has a greater affinity for the amino acid proline than Saccharomyces<ref name=Crauwels1> S. Crawels et. al. [http://link.springer.com/article/10.1007%2Fs00253-015-6769-9| Comparative phenomics and targeted use of genomics reveals variation in carbon and nitrogen assimilation among different Brettanomyces bruxellensis strains], 2015</ref>. There is some inter-strain variability on what sugars Brettanomyces can metabolize (arbutin, β-methyl-D-glucoside, et al. are only metabolized by some strains of Brettanomyces.)<ref name=Crauwels1> S. Crawels et. al. [http://link.springer.com/article/10.1007%2Fs00253-015-6769-9| Comparative phenomics and targeted use of genomics reveals variation in carbon and nitrogen assimilation among different Brettanomyces bruxellensis strains], 2015</ref>
Brettanomyces has been implicated in producing most of the aroma compounds in Lambic.<ref name="Guinard">Jean-Xavier Guinard, [[Books#Classic Beer Styles: Lambic|Classic Beer Styles: Lambic]], 1990</ref> Sensory-significant quantities of ethyl acetate and ethyl lactate form at this time from ethanol entering into an ester bond with [[Acetic acid|acetic]] and [[lactic acid]], respectively. In addition, ethylphenols formed from hydroxycinammic acid -- found in the grain used to make the wort -- contribute an odor often described as "horse sweat", "barnyard", or "leather" <ref name=Crauwels1> S. Crawels et. al. [http://link.springer.com/article/10.1007%2Fs00253-015-6769-9| Comparative phenomics and targeted use of genomics reveals variation in carbon and nitrogen assimilation among different Brettanomyces bruxellensis strains], 2015</ref> <ref name=Lentz1> M. Lentz and C. Harris. [https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0ahUKEwirpvaJlerMAhVBz2MKHXxYB_kQFggnMAE&url=http%3A%2F%2Fwww.mdpi.com%2F2304-8158%2F4%2F4%2F581%2Fpdf&usg=AFQjCNHZB4IHgQasVxVL3JjdmMcWjdFIUw&sig2=pJ8f-mmJKAYHIfO5xj7GhQ| Analysis of Growth Inhibition and Metabolism of Hydroxycinnamic Acids by Brewing and Spoilage Strains of Brettanomyces Yeast], 2015</ref>. The esterization process is greatly helped by the enzyme esterase provided by Brettanomyces. However, the enzymatic esterization is highly reversible and esters found in high concentrations in the lambic prior to the presence of the esterase will often achieve a lower equilibrium at the end of fermentation. This is the case with iso-amyl acetate, which is produced by Saccharomyces and is a characteristic odor compound in many other beers.
Tetrahydropyridines (THPs) produced by Brettanomyces (as well as some Lactobacilli) have a wide variety of odors and give lambic much of its "mousey" aroma, as well as cider- and horse-like aromas, though the concentrations and thus smells of THPs are variable.<ref name=Heresztyn1> T. Heresztyn [http://ajevonline.org/content/37/2/127.short| Formation of Substituted Tetrahydropyridines by Species of Brettanomyces and Lactobacillus Isolated from Mousy Wines], 1986</ref> Other important odor and flavor compounds produced by Brettanomyces include 4-ethylphenol, 4-ethylguaiacol, and isovaleric acid. 4-ethylphenol produces barnyard and horsey flavors which can taste like Band-aids in higher concentrations. 4-ethylguaiacol lends spicier flavors of bacon and cloves and can be smoky, while isovaleric acid gives lambic its sweaty and cheesy flavors and odors.