Changes

As beer ages, different flavor and aroma compounds both deteriorate and form over timeand at different rates. This is a complex collection of changes with many variables involved in affecting different compounds in different ways. As molecules deteriorate or are formed, their associated flavors not only dissapate dissipate and appear, but the influence that they have on each other may emphasize or overwhelm other flavors. The compounds, which number in the hundreds or perhaps thousands, are not in equilibrium when the beer is packaged. Once bottled or kegged, this closed environment forces molecules to reach a status of minimal energy and maximal entropy, and thus many of the molecules change over time to reach equilibrium. The two largest factors that affect beer aging are temperature and dissolved oxygen in the package <ref name="Vanderhaegen_2006" />. UnfortunatelyRegular beers with a lower pH tend to age faster, however, most beer studies have focused on lager beers and some on ales and strong beers. Research on beers containing living ''Brettanomyces'' or beers that are at a lower pH of 3-3.8 is limited.

(This In beer, oxidation is probably the most important thing process of carbon-based molecules losing electrons to talk about firstoxygen atoms or free radicals <ref>[https://en.wikipedia.org/wiki/Redox Wikipedia. "Redox". Retrieved 09/03/2017.]</ref>. Oxidation increases the amount of off-flavor compounds, as well as dulls the aroma of beer. Brewers yeast and ''Brettanomyces'' are great scavengers of oxygen, and adding fresh yeast and sugar at packaging can help reduce dissolved oxygen in the package, and even reverse some effects of oxidation. Adding fresh yeast and sugar can reduce aldehydes and ketones such as acetaldehyde, trans-2-nonenol, and diacetyl, back into ethanol after packaging <ref>[http://pubs.acs.org/doi/abs/10.1021/jf9037387 Daan Saison, David P. De Schutter, Nele Vanbeneden, Luk Daenen, Filip Delvaux and Freddy R. Delvaux. 2010.]</ref><ref name="hall_mitchell" />.)

In beergeneral, oxidation the best practice is the process of carbon based molecules losing electrons to limit oxygen atoms or free radicals at packaging time, although brewers have had success packaging beers with living ''Brettanomyces'' without purging the bottles with CO<refsup>[https://en.wikipedia.org/wiki/Redox Wikipedia. "Redox". Retrieved 09/03/2017.]2</refsup>. Oxidation increases the amount of offOther compounds can serve as anti-flavor compoundsoxidants in beer. For example, sulfates are converted into sulfites by yeast, as well as dulls and sulfites postpone the aroma formation of beerfree radicals. Brewers yeast Lower-weight polyphenols, which originate from malt (70-80%) and ''Brettanomyces'' hops (20-30%), are great thought to be free radical scavengers of oxygenand anti-oxidants, however other polyphenols have been identified as pro-oxidants and adding fresh yeast and sugar at packaging can help reduce dissolved oxygen the effectiveness of antioxidant activity in general for polyphenols is debatable in the scientific literature (although their impact in the packagemash and boil has been established as positive). Maillard reactions from malting/roasting and wort boiling also create anti-oxidants, and even reverse some affects of oxidationin general the darker the roasting the more anti-oxidant the malts will be <ref name="Vanderhaegen_2006" />. Adding fresh yeast Lactic acid and sugar can reduce aldehydes and ketones such lactic acid fermentation are thought to also help serve as acetaldehyde, transanti-2-nonenoloxidants, although this has not be studied in sour beer <ref>[https://www.ncbi.nlm.nih.gov/pubmed/10904049 Free radical scavenging and diacetylantioxidant effects of lactate ion: an in vitro study. Groussard C, Morel I, Chevanne M, Monnier M, Cillard J, back into ethanol after packaging Delamarche A. 1985.]</ref><ref>[httphttps://pubswww.acssciencedirect.orgcom/doiscience/absarticle/10.1021pii/jf9037387 Daan SaisonS0740002011000530 Effect of lactic acid fermentation on antioxidant, texture, David Pcolor and sensory properties of red and green smoothies. De Schutter Raffaella Di Cagno, Giovanna Minervini, Nele VanbenedenCarlo G. Rizzello, Luk DaenenMaria De Angelis, Filip Delvaux and Freddy R. DelvauxMarco Gobbetti. 20102011.]</ref><ref name="hall_mitchell" />.