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In beer, oxidation is the process of carbon based molecules losing electrons to oxygen atoms or other 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 affects 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" />.