In brewing, dissolved oxygen (DO) is measured for two reasons. The first is to determine that sufficient oxygen is dissolved in wort to initiate a clean, vigorous fermentation. The second is to determine that a low enough level remains in packaged beer to prevent staling. For homebrewers and nanobrewers, the aeration of wort is the primary consideration, which is just as well since measuring the very low level in packaged beer is a much more advanced and expensive technique. BYO’s Technical Editor Ashton Lewis breaks down DO so you can better understand this topic often overheard in breweries.