Changes

==Chemical Changes==

As beer ages, different flavor and aroma compounds both deteriorate and form over time. This is a complex collection of changes with many variables affecting different compounds in different ways. As molecules deteriorate or are formed, their associated flavors not only dissapate 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" />. Unfortunately, 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.