Changes

==Chemical Changes=====Sensory Changes===

Beer aging is a complicated subject, and every beer ages differently. In general, sensory changes include a slow and gradual and steady decline in bitterness, partly due to an increase in a honey/toffee-like sweetness in the aroma and taste. Another flavor described as 'ribes', which is a sort of black currant taste, rises quickly sometime after packaging, and then gradually declines over time. After the 'ribes' flavor, a cardboard flavor slowly develops. Other findings claim that the cardboard flavor increases to a maximum, and then begins to decline after some time. Other changes include a rise in harsh, astringent notes in some beers, while wine and whiskey notes develop in very old beers. Positive flavors such as fruity esters and hop character fade considerably. These changes are not always seen as negative changes; studies have been done that show that drinkers sometimes prefer aged beers over young ones (even in light lagers). While the cardboard flavor has historically been emphasized in beer staling, it is just one component of beer aging. Many other flavor changes can occur, depending on the beer. For example, stronger beers have been found to develop burn, caramel, alcohol, licorice, and Sherry characters and no cardboard flavors. The development of many of these flavors corresponds with the amount of dissolved oxygen in the packaged beer and storage temperature <ref name="Vanderhaegen_2006">[http://www.sciencedirect.com/science/article/pii/S0308814605000865 The chemistry of beer aging – a critical review. Bart Vanderhaegen, Hedwig Neven, Hubert Verachtert, Guy Derdelinckx. 2006. DOI:https://doi.org/10.1016/j.foodchem.2005.01.006.]</ref>.  ==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 disappate 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 equilibium. 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 ''Brettanoyces'' or beers that are at a lower pH of 3-3.8 is limited.