13,591
edits
Changes
no edit summary
See also:
* [https://encyclopedia.pub/item/revision/d2232da8945e383a5a0cdf189b38a2d8 "Bottle Conditioning," Topic Review by Kateřina Štulíková and Pavel Dostálek, Scholarly Community Encyclopedia.]
* [[Packaging#Oxygen_exposure|Packaging and Oxygen Exposure.]]
* [https://www.facebook.com/groups/MilkTheFunk/permalink/2282287018466166/ Justin Amaral's can conditioning project with DO tracking for canned conditioned beers on MTF.]
[http://www.sciencedirect.com/science/article/pii/S0740002014002548 Spitaels et al., 2015 microbes in bottles of gueuze]
[https://www.facebook.com/groups/MilkTheFunk/posts/7284659538228864/ Anecdotal evidence that ''Brettanomyces'' can reverse discoloration from enzymatic browning.]
See also [[Commercial Sour Beer Dregs Inoculation]].
* [https://jp.hach.com/asset-get.download.jsa?id=50544340479 Industry standards of dissolved oxygen levels in beer throughout the brewing process, by Hach.]
* [https://www.facebook.com/groups/MilkTheFunk/permalink/3835629766465209/ MTF thread on anecdotal accounts of ''Brettanomyces'' affecting oxidation character in beer.]
* [https://suigenerisbrewing.com/index.php/2022/03/12/metabisulfite-7-year-experiment/ Dr. Bryan Heit explanations chemical oxidation pathways, and the use of metabisulfite to limit oxidation in packaging.]
===General Effects of Temperature===
[https://en.wikipedia.org/wiki/Polyphenol Polyphenols] are a large group of organic chemicals characterized by many phenol structures combined. Subclasses of polyphenols include tannic acid, tannins, and flavonoids <ref name="wikipedia_polyphenols" /><ref>[https://en.wikipedia.org/wiki/Flavonoid Flavonoid. Wikipedia website. Retrieved 05/02/2017.]</ref>.
Polyphenols have an ambiguous role in the aging of beer. Flavonoids (for example catechin, which comes from hops and is a major source of polyphenols in beer), are antioxidants and protect more sensitive compounds such as isohumulones from oxidation by scavenging free radicals and binding with oxidative metals (iron, for example). However, they themselves can also be oxidized over time to possibly create off-flavors. In addition to their own oxidation, [https://en.wikipedia.org/wiki/Hydroxyl_radical hydroxyl radicals] that cause oxidation also react highly with ethanol, and therefore a portion may not react with polyphenols. After a lag period of 5 weeks in the bottle, it was found that levels of tannins actually increase. This is thought to be caused by smaller flavonoids reacting with acetaldehyde. Polyphenols were also oxidized into [https://en.wikipedia.org/wiki/Quinone quinones], which are a stepping stone in the reaction that causes [https://en.wikipedia.org/wiki/Food_browning oxidative food browning](this reaction increases in the presence of acids <ref>[https://en.wikipedia.org/wiki/Quinone#Reduction "Quinone". Wikipedia. Retrieved 12/23/2023.]</ref>). The use of polyphenols during mashing and boiling has been shown to decrease trans-2-nonenal (cardboard flavor) and trans-2-nonenal that is protected from fermentation by being bound to proteins (see [[Aging_and_Storage#Tannic_Acid|Tannic Acid]] below). In two studies, there appeared to be no significant effect on free radical formation by polyphenols, probably due to the fact that they readily react with ethanol <ref name="Callemien_2010" />.
Higher temperatures increase the rate of oxidized polyphenols. In one study on aged lagers, 6.5% of the polyphenols were oxidized after 5 days at 40°C/104°F, but only 0.6% of the polyphenols were oxidized after 9 months at 20°C/68°F <ref name="Callemien_2010" />.
- https://pubs.rsc.org/en/content/articlelanding/2004/pp/b316210a/unauth#!divAbstract
Iso-alpha acids will skunk if exposed to UV light. Oxidized alpha acids (humulinones) will also skunk if exposed to UV light <ref>[https://www.homebrewersassociation.org/how-to-brew/resources/conference-seminars Dr. Patricia Aron. "Bitterness and the IBU: What’s It All About?" HomebrewCon 2017 Presentation. ~32 mins in. Retrieved 09/05/2017.]</ref>.This compound is known as 3-methyl-2-butene-1-thiol (3MBT). Brown bottles filter most UV light, while green bottles only filter a portion of UV light. See [https://beerandbrewing.com/dictionary/eIXf22Zwnt/ "Lightstruck", Craft beer and Brewing Magazine website]. * [https://www.youtube.com/watch?app=desktop&v=W4vJ9DhoLp4&t=774s Olivier Dedeycker explains why Saison Dupont is packaged in brown bottles for the US market and green bottles for the European market.]
====Damascenone====
Products of Maillard reactions, which include a diverse range of reactions, have also been found in beer, although research in this area is limited. Some Maillard compounds found in aging beer remain under taste threshold, for example, furfural and 5-hydroxymethyl furfural. It is hypothesized that a wide range of unknown Maillard reactions and their intermediates might play a role in the aging of beer. In particular, the bready, sweet, caramel and wine-like character of stale beer might be due to Maillard reactions <ref name="Vanderhaegen_2006" />.
In general, lower storage temperatures preserve hop compounds. Cans also help preserve some hop compounds versus bottles because bottle caps can strip certain hop compounds such as myrcene and caryophyllene when stored at room temperature (less so when stored cold). For example, one study found a moderate amount of degradation of humulinones, iso-α-acids, and residual α-acids when dry hopped beers were stored at 20°C versus 3°C. There was also an overall decrease in hop aroma compounds during warm storage, with some esters, hop monoterpenes, and sesquiterpenes showing poor storage stability compared to other ester compounds, monoterpene alcohols, and ketones which increased during warm storage. After 10 months of storage, the dry hopped beers stored at 20°C had a significant drop in floral, citrus and tropical fruit notes when compared to the same beers stored at 3°C <ref>[https://onlinelibrary.wiley.com/doi/full/10.1002/jib.667 Kemp, O., Hofmann, S., Braumann, I., Jensen, S., Fenton, A., and Oladokun, O. (2021) Changes in key hop-derived compounds and their impact on perceived dry-hop flavour in beers after storage at cold and ambient temperature. J. Inst. Brew., https://doi.org/10.1002/jib.667.]</ref>.
[[Tetrahydropyridine]] (THP) is a compound that tastes like Cheerios® or corn tortilla chips that often develops soon after packaging beers that contain ''Brettanomyces'' or heterofermentative ''Lactobacillus''. It is usually detected after swallowing the beer. This compound is stimulated by oxygen, and often ages out after a few months. See the [[Tetrahydropyridine]] page for more information.