Microbiology and Biochemistry: Difference between revisions

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The enteric stage

Lambic wort arrives in the coolship at approximately 5% sugar per weight of water, along with an assortment of proteins and fatty acids and other compounds <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>. Negligible ethanol is present prior to fermentation, nor is there much of the organic acids that will give lambic its characteristic tartness; the wort has a pH around ~~4.8~~, which is similar to the wort of other beers. Enteric bacteria, including Enterobacter hormaechei, E. kobei, Klebsiella pneumoniae, and Escherichia coli, are the first to gain a foothold in this environment, with significant numbers found after three to four days. The enteric bacteria primarily consume glucose, which reduces the gravity of the wort from ~1.050 to ~1.040 after the first three weeks.

Lambic wort arrives in the coolship at approximately 5% sugar per weight of water, along with an assortment of proteins and fatty acids and other compounds <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>. Negligible ethanol is present prior to fermentation, nor is there much of the organic acids that will give lambic its characteristic tartness; the wort has a pH around 5, which is similar to the wort of other beers. <ref name=Oevelen77 >D. Van Oevelen, M. Spaepen, P. Timmermans and H. Verachtert, [http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1977.tb03825.x/abstract| MICROBIOLOGICAL ASPECTS OF SPONTANEOUS WORT FERMENTATION IN THE PRODUCTION OF LAMBIC AND GUEUZE], 1977</ref> Enteric bacteria, including Enterobacter hormaechei, E. kobei, Klebsiella pneumoniae, and Escherichia coli, are the first to gain a foothold in this environment, with significant numbers found after three to four days. The enteric bacteria primarily consume glucose, which reduces the gravity of the wort from ~1.050 to ~1.040 after the first three weeks.

Enteric bacteria are responsible for the production of [[acetic acid]], and the pH of the wort falls from around 5 to 4.5 in the first week of fermentation. The 40 to 120 mg/L acetic acid found in the wort after the first week is very close to the amount found in the final product <ref name=Oevelen77 >D. Van Oevelen, M. Spaepen, P. Timmermans and H. Verachtert, [http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1977.tb03825.x/abstract|MICROBIOLOGICAL ASPECTS OF SPONTANEOUS WORT FERMENTATION IN THE PRODUCTION OF LAMBIC AND GUEUZE], 1977</ref>

Enteric bacteria are responsible for the production of [[acetic acid]], and the pH of the wort falls from around 5 to 4.5 in the first week of fermentation. The 40 to 120 mg/L acetic acid found in the wort after the first week is very close to the amount found in the final product.<ref name=Oevelen77 >D. Van Oevelen, M. Spaepen, P. Timmermans and H. Verachtert, [http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1977.tb03825.x/abstract| MICROBIOLOGICAL ASPECTS OF SPONTANEOUS WORT FERMENTATION IN THE PRODUCTION OF LAMBIC AND GUEUZE], 1977</ref>

<ref name=sour>John Edwards and Adam DiCaprio. [http://www.process-nmr.com/pdfs/Edwards%20-%20SMASH%202014%20-%20MNova%20Users%20Meeting%20-%209-7-14.pdf|When Beer Goes Sour: An NMR Investigation], Mestrelab

MNova Users Meeting, SMASH – Atlanta, GA, September 7, 2014</ref>. Significant changes to the concentration of acetic acid should not occur until the ethanol has a chance to oxidize in aging in the bottle over many years or even decades [6]. The pellicle that forms on the top of the wort forms around ___ days, and is likely the product of acetobacteria during the enteric phase [9].

MNova Users Meeting, SMASH – Atlanta, GA, September 7, 2014</ref> Significant changes to the concentration of acetic acid should not occur until the ethanol has a chance to oxidize in aging in the bottle over many years or even decades [6]. The pellicle that forms on the top of the wort forms around ___ days, and is likely the product of acetobacteria during the enteric phase [9].

Low pH (below ~4.5) and an ethanol concentration higher than ~2% by volume is a hostile environment to the enterobacteria, and Saccromyces species are able to dominate in the wort once these conditions occur around 30-60 days into fermentation.

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Continued aging

Eventually even the slow-fermenting Brettanomyces runs out of fermentable sugars and fermentation draws to a slow close. The beer will continue to change and evolve over time, though minimal interaction with active yeast occurs. This stage is marked by oxidation and breakdown of the more complex parts of the yeast itself <ref name=Dalgliesh >C. E. Dalgliesh, Flavour stability, [http://www.europeanbreweryconvention.org/EBCmain/organisation/publication.php|Proceedings of the European Brewery Convention Congress], 1977</ref> <ref name=Vanderhaegen >B. Vanderhaegen, H. Neven, H. Verachtert, and G. Derdelinckx, [http://www.sciencedirect.com/science/article/pii/S0308814605000865|The chemistry of beer aging – a critical review], 2006</ref>.

Eventually even the slow-fermenting Brettanomyces runs out of fermentable sugars and fermentation draws to a slow close. The beer will continue to change and evolve over time, though minimal interaction with active yeast occurs. This stage is marked by oxidation and breakdown of the more complex parts of the yeast itself.<ref name=Dalgliesh >C. E. Dalgliesh, Flavour stability, [http://www.europeanbreweryconvention.org/EBCmain/organisation/publication.php|Proceedings of the European Brewery Convention Congress], 1977</ref> <ref name=Vanderhaegen >B. Vanderhaegen, H. Neven, H. Verachtert, and G. Derdelinckx, [http://www.sciencedirect.com/science/article/pii/S0308814605000865|The chemistry of beer aging – a critical review], 2006</ref>

While oxidation can occur rapidly due to a break in the fidelity of the seal at the cork, oxidation can still occur without the passage of oxygen through the cork or significant oxygen gas in the headspace due to the transfer of oxygen from an oxygen-containing compound like ____ or ____ in the wort to others. The act of losing an oxygen, or more generally, of losing electrons, is called reduction. Reduction of ____ by ____ to (E)-2-nonenal has been implicated as being of primary importance to the long-term oxidation of flavor compounds in beer <ref name=Jamieson > A. M. Jamieson, E. C. Chen, and J. E. A. Van Gheluwe, A study of the cardboard flavour in beer by gas chromatography, [http://www.asbcnet.org/publications/journal/Pages/default.aspx|Proceedings of the American Society of Brewing Chemists], 1969</ref>, which leads to a characteristic flavor of oxidized beer, commonly described as being of "wet cardboard". However, many other processes and compounds are important to the ageing of beer as well.

While oxidation can occur rapidly due to a break in the fidelity of the seal at the cork, oxidation can still occur without the passage of oxygen through the cork or significant oxygen gas in the headspace due to the transfer of oxygen from an oxygen-containing compound like ____ or ____ in the wort to others. The act of losing an oxygen, or more generally, of losing electrons, is called reduction. Reduction of ____ by ____ to (E)-2-nonenal has been implicated as being of primary importance to the long-term oxidation of flavor compounds in beer, <ref name=Jamieson > A. M. Jamieson, E. C. Chen, and J. E. A. Van Gheluwe, A study of the cardboard flavour in beer by gas chromatography, [http://www.asbcnet.org/publications/journal/Pages/default.aspx|Proceedings of the American Society of Brewing Chemists], 1969</ref> which leads to a characteristic flavor of oxidized beer, commonly described as being of "wet cardboard". However, many other processes and compounds are important to the ageing of beer as well.

The decomposition of the yeast leads to _____.

@@ Line 19: / Line 19: @@
 The enteric stage
-Lambic wort arrives in the coolship at approximately 5% sugar per weight of water, along with an assortment of proteins and fatty acids and other compounds <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>. Negligible ethanol is present prior to fermentation, nor is there much of the organic acids that will give lambic its characteristic tartness; the wort has a pH around 4.8, which is similar to the wort of other beers. Enteric bacteria, including Enterobacter hormaechei, E. kobei, Klebsiella pneumoniae, and Escherichia coli, are the first to gain a foothold in this environment, with significant numbers found after three to four days. The enteric bacteria primarily consume glucose, which reduces the gravity of the wort from ~1.050 to ~1.040 after the first three weeks.
+Lambic wort arrives in the coolship at approximately 5% sugar per weight of water, along with an assortment of proteins and fatty acids and other compounds <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>. Negligible ethanol is present prior to fermentation, nor is there much of the organic acids that will give lambic its characteristic tartness; the wort has a pH around 5, which is similar to the wort of other beers. <ref name=Oevelen77 >D. Van Oevelen, M. Spaepen, P. Timmermans and H. Verachtert, [http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1977.tb03825.x/abstract| MICROBIOLOGICAL ASPECTS OF SPONTANEOUS WORT FERMENTATION IN THE PRODUCTION OF LAMBIC AND GUEUZE], 1977</ref> Enteric bacteria, including Enterobacter hormaechei, E. kobei, Klebsiella pneumoniae, and Escherichia coli, are the first to gain a foothold in this environment, with significant numbers found after three to four days. The enteric bacteria primarily consume glucose, which reduces the gravity of the wort from ~1.050 to ~1.040 after the first three weeks.
-Enteric bacteria are responsible for the production of [[acetic acid]], and the pH of the wort falls from around 5 to 4.5 in the first week of fermentation. The 40 to 120 mg/L acetic acid found in the wort after the first week is very close to the amount found in the final product <ref name=Oevelen77 >D. Van Oevelen, M. Spaepen, P. Timmermans and H. Verachtert, [http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1977.tb03825.x/abstract|MICROBIOLOGICAL ASPECTS OF SPONTANEOUS WORT FERMENTATION IN THE PRODUCTION OF LAMBIC AND GUEUZE], 1977</ref>
+Enteric bacteria are responsible for the production of [[acetic acid]], and the pH of the wort falls from around 5 to 4.5 in the first week of fermentation. The 40 to 120 mg/L acetic acid found in the wort after the first week is very close to the amount found in the final product.<ref name=Oevelen77 >D. Van Oevelen, M. Spaepen, P. Timmermans and H. Verachtert, [http://onlinelibrary.wiley.com/doi/10.1002/j.2050-0416.1977.tb03825.x/abstract| MICROBIOLOGICAL ASPECTS OF SPONTANEOUS WORT FERMENTATION IN THE PRODUCTION OF LAMBIC AND GUEUZE], 1977</ref>
 <ref name=sour>John Edwards and Adam DiCaprio. [http://www.process-nmr.com/pdfs/Edwards%20-%20SMASH%202014%20-%20MNova%20Users%20Meeting%20-%209-7-14.pdf|When Beer Goes Sour: An NMR Investigation], Mestrelab
-MNova Users Meeting, SMASH – Atlanta, GA, September 7, 2014</ref>. Significant changes to the concentration of acetic acid should not occur until the ethanol has a chance to oxidize in aging in the bottle over many years or even decades [6]. The pellicle that forms on the top of the wort forms around ___ days, and is likely the product of acetobacteria during the enteric phase [9].
+MNova Users Meeting, SMASH – Atlanta, GA, September 7, 2014</ref> Significant changes to the concentration of acetic acid should not occur until the ethanol has a chance to oxidize in aging in the bottle over many years or even decades [6]. The pellicle that forms on the top of the wort forms around ___ days, and is likely the product of acetobacteria during the enteric phase [9].
 Low pH (below ~4.5) and an ethanol concentration higher than ~2% by volume is a hostile environment to the enterobacteria, and Saccromyces species are able to dominate in the wort once these conditions occur around 30-60 days into fermentation.
@@ Line 55: / Line 55: @@
 Continued aging
-Eventually even the slow-fermenting Brettanomyces runs out of fermentable sugars and fermentation draws to a slow close. The beer will continue to change and evolve over time, though minimal interaction with active yeast occurs. This stage is marked by oxidation and breakdown of the more complex parts of the yeast itself <ref name=Dalgliesh >C. E. Dalgliesh, Flavour stability, [http://www.europeanbreweryconvention.org/EBCmain/organisation/publication.php|Proceedings of the European Brewery Convention Congress], 1977</ref> <ref name=Vanderhaegen >B. Vanderhaegen, H. Neven, H. Verachtert, and G. Derdelinckx, [http://www.sciencedirect.com/science/article/pii/S0308814605000865|The chemistry of beer aging – a critical review], 2006</ref>.
+Eventually even the slow-fermenting Brettanomyces runs out of fermentable sugars and fermentation draws to a slow close. The beer will continue to change and evolve over time, though minimal interaction with active yeast occurs. This stage is marked by oxidation and breakdown of the more complex parts of the yeast itself.<ref name=Dalgliesh >C. E. Dalgliesh, Flavour stability, [http://www.europeanbreweryconvention.org/EBCmain/organisation/publication.php|Proceedings of the European Brewery Convention Congress], 1977</ref> <ref name=Vanderhaegen >B. Vanderhaegen, H. Neven, H. Verachtert, and G. Derdelinckx, [http://www.sciencedirect.com/science/article/pii/S0308814605000865|The chemistry of beer aging – a critical review], 2006</ref>
-While oxidation can occur rapidly due to a break in the fidelity of the seal at the cork, oxidation can still occur without the passage of oxygen through the cork or significant oxygen gas in the headspace due to the transfer of oxygen from an oxygen-containing compound like ____ or ____ in the wort to others. The act of losing an oxygen, or more generally, of losing electrons, is called reduction. Reduction of ____ by ____ to (E)-2-nonenal has been implicated as being of primary importance to the long-term oxidation of flavor compounds in beer <ref name=Jamieson > A. M. Jamieson, E. C. Chen, and J. E. A. Van Gheluwe, A study of the cardboard flavour in beer by gas chromatography, [http://www.asbcnet.org/publications/journal/Pages/default.aspx|Proceedings of the American Society of Brewing Chemists], 1969</ref>, which leads to a characteristic flavor of oxidized beer, commonly described as being of "wet cardboard". However, many other processes and compounds are important to the ageing of beer as well.
+While oxidation can occur rapidly due to a break in the fidelity of the seal at the cork, oxidation can still occur without the passage of oxygen through the cork or significant oxygen gas in the headspace due to the transfer of oxygen from an oxygen-containing compound like ____ or ____ in the wort to others. The act of losing an oxygen, or more generally, of losing electrons, is called reduction. Reduction of ____ by ____ to (E)-2-nonenal has been implicated as being of primary importance to the long-term oxidation of flavor compounds in beer, <ref name=Jamieson > A. M. Jamieson, E. C. Chen, and J. E. A. Van Gheluwe, A study of the cardboard flavour in beer by gas chromatography, [http://www.asbcnet.org/publications/journal/Pages/default.aspx|Proceedings of the American Society of Brewing Chemists], 1969</ref> which leads to a characteristic flavor of oxidized beer, commonly described as being of "wet cardboard". However, many other processes and compounds are important to the ageing of beer as well.
 The decomposition of the yeast leads to _____.