The machine saves time by combining home brewing's longest steps—fermentation, which usually takes a week, and carbonation, which can take at least two. The fermentation tank is also a pressure vessel, which traps carbon dioxide released by yeast, force-carbonating the beer. The system also does away with two common foes of freshness: the sealed vessel keeps out oxygen, a culprit behind flat-tasting pints; and a valve at the bottom of the tank isolates the yeast from the beer as soon as fermenting is done, which prevents meaty, off flavors.