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Oxidation (edit)

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=== Catalysts ===
=== Catalysts ===
A catalyst increases the speed of a chemical reaction without being consumed by the process. Therefore, catalysts can greatly promote a reaction even in very small amounts.
A catalyst increases the speed of a chemical reaction without being consumed by the process. Therefore, catalysts can greatly promote a reaction even in very small amounts.
[[Transition metals]] promote oxidation reactions,<ref name=merkun>Mertens T, Kunz T, Wietstock PC, Methner FJ. [https://onlinelibrary.wiley.com/doi/full/10.1002/jib.673 Complexation of transition metals by chelators added during mashing and impact on beer stability.] ''J Inst Brew.'' 2021;127(4):345–357.</ref><ref name=Irwin/><ref name=bamlen/> and can be introduced from several sources:
* Malt is the primary source of metals.<ref name=merkun/><ref name=merkunmet/><ref name=mai>Maia CR. [https://repositorio-aberto.up.pt/bitstream/10216/112347/2/269942.pdf Stability of beer through control of minerals in sweet wort.] Master's thesis. University of Porto. 2018.
</ref><ref name=pagmai/> Depending on the malts used, a standard wort has levels of around 100-270 μg/L [[iron]], 20-400 μg/L [[copper]], and 80-150 μg/L [[manganese]].<ref name=merkun/> As little as 10 μg/L of these metals can make a detectable difference to the oxidative stability.<ref name=merkun/>
* Hops are a relatively substantial source of manganese in beer (and especially so with dry hopping).<ref name=merkunmet/>
* Brewing liquor may contain metals; for example, some sources of water contain high levels of iron.
* Metallic brewing gear can contribute metals through contact with brewing liquor, wort, or beer; examples include [[copper]] wort chillers and [[stainless steel]] kegs.<ref name=narziss1986/>
* Brewing additives can contain metals. For example, some yeast nutrient products contain manganese.


Malt naturally contains the following [[enzymes]] that promote oxidation reactions during [[mashing]] (then they are destroyed by [[boiling]]):<ref>Kunze W. Hendel O, ed. [[Library|''Technology Brewing & Malting.'']] 6th ed. VLB Berlin; 2019:214.</ref><ref name=mullerr/><ref name=cargon/>
Malt naturally contains the following [[enzymes]] that promote oxidation reactions during [[mashing]] (then they are destroyed by [[boiling]]):<ref>Kunze W. Hendel O, ed. [[Library|''Technology Brewing & Malting.'']] 6th ed. VLB Berlin; 2019:214.</ref><ref name=mullerr/><ref name=cargon/>
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* Ascorbic acid oxidase - catalyzes the oxidation of [[ascorbic acid]] by oxygen (O<sub>2</sub>).<ref name=kanoxi/> Very active during mashing and fairly heat-stable<ref name=kanbam/>
* Ascorbic acid oxidase - catalyzes the oxidation of [[ascorbic acid]] by oxygen (O<sub>2</sub>).<ref name=kanoxi/> Very active during mashing and fairly heat-stable<ref name=kanbam/>
* Oxalate oxidase (AKA germin) - catalyses the conversion of oxalate into carbon dioxide and hydrogen peroxide. pH optimum of approximately 4.0 but active over a large range. Because the enzyme is active in a broad pH range, and because it has high heat tolerance, it was active during mashing, but it was less important than other oxidases for scavenging oxygen from mashes because of its low affinity for oxygen.<ref name=kanoxi/> highly active.<ref name=kanbam>Kanauchi M, Bamforth CW. [https://www.themodernbrewhouse.com/wp-content/uploads/2019/02/BrewingScience_bamforth_82-84.pdf A Challenge in the study of flavour instability.] ''BrewingScience - Monatsschrift Brauwiss.'' 2018;71(Sept/Oct):82–84.</ref>
* Oxalate oxidase (AKA germin) - catalyses the conversion of oxalate into carbon dioxide and hydrogen peroxide. pH optimum of approximately 4.0 but active over a large range. Because the enzyme is active in a broad pH range, and because it has high heat tolerance, it was active during mashing, but it was less important than other oxidases for scavenging oxygen from mashes because of its low affinity for oxygen.<ref name=kanoxi/> highly active.<ref name=kanbam>Kanauchi M, Bamforth CW. [https://www.themodernbrewhouse.com/wp-content/uploads/2019/02/BrewingScience_bamforth_82-84.pdf A Challenge in the study of flavour instability.] ''BrewingScience - Monatsschrift Brauwiss.'' 2018;71(Sept/Oct):82–84.</ref>
* Glucose oxidase?
[[Transition metals]] promote oxidation reactions,<ref name=merkun>Mertens T, Kunz T, Wietstock PC, Methner FJ. [https://onlinelibrary.wiley.com/doi/full/10.1002/jib.673 Complexation of transition metals by chelators added during mashing and impact on beer stability.] ''J Inst Brew.'' 2021;127(4):345–357.</ref><ref name=Irwin/><ref name=bamlen/> and can be introduced from several sources:
* Malt is the primary source of metals.<ref name=merkun/><ref name=merkunmet/><ref name=mai>Maia CR. [https://repositorio-aberto.up.pt/bitstream/10216/112347/2/269942.pdf Stability of beer through control of minerals in sweet wort.] Master's thesis. University of Porto. 2018.
</ref><ref name=pagmai> Depending on the malts used, a standard wort has levels of around 100-270 μg/L [[iron]], 20-400 μg/L [[copper]], and 80-150 μg/L [[manganese]].<ref name=merkun/> As little as 10 μg/L of these metals can make a detectable difference to the oxidative stability.<ref name=merkun/>
* Hops are a relatively substantial source of manganese in beer (and especially so with dry hopping).<ref name=merkunmet/>
* Brewing liquor may contain metals; for example, some sources of water contain high levels of iron.
* Metallic brewing gear can contribute metals through contact with brewing liquor, wort, or beer; examples include [[copper]] wort chillers and [[stainless steel]] kegs.<ref name=narziss1986/>
* Brewing additives can contain metals. For example, some yeast nutrient products contain manganese.


Light catalyzes oxidation reactions.<ref name=hawmor/><ref name=muller95/> The influence of light was thought to be overcome by using brown bottles. But even in brown bottles, light exercises an influence during long storage times (for instance on the shelves in supermarkets).<ref name=narziss1986/>
Light catalyzes oxidation reactions.<ref name=hawmor/><ref name=muller95/> The influence of light was thought to be overcome by using brown bottles. But even in brown bottles, light exercises an influence during long storage times (for instance on the shelves in supermarkets).<ref name=narziss1986/>
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== Potential sources ==
== Potential sources ==
*[http://www.themodernbrewhouse.com/wp-content/uploads/2017/03/Baert-Aldehyden.pdf On the Origin of Free and Bound Staling Aldehydes in Beer]
*[http://www.themodernbrewhouse.com/wp-content/uploads/2017/03/Baert-Aldehyden.pdf On the Origin of Free and Bound Staling Aldehydes in Beer]
*[https://www.tandfonline.com/doi/abs/10.1080/03610470.2020.1795609 Retention of Iron and Copper during Mashing of Roasted Malts]
*[https://www.tandfonline.com/doi/abs/10.1094/ASBCJ-57-0034 Estimation of Antioxidative Activity and its Relationship to Beer Flavor Stability]
*[https://www.tandfonline.com/doi/abs/10.1094/ASBCJ-57-0034 Estimation of Antioxidative Activity and its Relationship to Beer Flavor Stability]
*Anne M. Frederiksen, Rikke M. Festersen and Mogens L. Andersen . Oxidative Reactions during Early Stages of Beer Brewing Studied by Electron Spin Resonance and Spin Trapping. Journal of Agricultural and Food Chemistry 2008, 56 (18) , 8514-8520.
*Anne M. Frederiksen, Rikke M. Festersen and Mogens L. Andersen . Oxidative Reactions during Early Stages of Beer Brewing Studied by Electron Spin Resonance and Spin Trapping. Journal of Agricultural and Food Chemistry 2008, 56 (18) , 8514-8520.
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