Microbiology and Biochemistry: Difference between revisions
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Interestingly, lactic acid bacteria have been implicated in racemizing amino acids in beer, causing Lambic (and other beers which make use of lactic acid bacteria such as Berliner Wiesse) to have a high percentage of right-handed amino acid stereoisomers relative to both their starting materials and other beers.<ref name=Erbe >T. Erbe and H. Brückner, [http://www.sciencedirect.com/science/article/pii/S0021967300002557|Chromatographic determination of amino acid enantiomers in beers and raw materials used for their manufacture], 2000</ref> | Interestingly, lactic acid bacteria have been implicated in racemizing amino acids in beer, causing Lambic (and other beers which make use of lactic acid bacteria such as Berliner Wiesse) to have a high percentage of right-handed amino acid stereoisomers relative to both their starting materials and other beers.<ref name=Erbe >T. Erbe and H. Brückner, [http://www.sciencedirect.com/science/article/pii/S0021967300002557|Chromatographic determination of amino acid enantiomers in beers and raw materials used for their manufacture], 2000</ref> | ||
== | ==Brettanomyces dominance== | ||
Brettanomyces inherits the role of most prominant yeast genera from Saccharomyces around 8 months, and continues consuming sugar 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 inherits the role of most prominant yeast genera from Saccharomyces around 8 months, and continues consuming sugar 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". | ||
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. 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 achieve a lower equilibrium. 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. | 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. 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 achieve a lower equilibrium. 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. | ||