After an initial or primary fermentation, beer is conditioned, matured, or aged in one of several ways which can take from 2 to 4 weeks, several months, or several years, depending on the brewer’s intention for the beer. The beer is usually transferred into a second container, so that it is no longer exposed to the dead yeast and other debris (also known as “trub”) that have settled to the bottom of the primary fermenter. This prevents the formation of unwanted flavours and harmful compounds such as acetaldehyde
Kräusening is a conditioning method in which fermenting wort is added to the finished beer. The active yeast will restart fermentation in the finished beer, and so introduce fresh carbon dioxide; the conditioning tank will be then sealed so that the carbon dioxide is dissolved into the beer producing a lively “condition” or level of carbonation. The kräusening method may also be used to condition bottled beer
Lagers are stored at cellar temperature or below for 1–6 months while still on the yeast The process of storing, or conditioning, or maturing, or aging a beer at a low temperature for a long period is called “lagering”, and while it is associated with lagers, the process may also be done with ales, with the same result – that of cleaning up various chemicals, acids, and compounds
During secondary fermentation, most of the remaining yeast will settle to the bottom of the second fermenter, yielding a less hazy product.
Some beers undergo an additional fermentation in the bottle giving natural carbonation This may be a second and/or third fermentation. They are bottled with a viable yeast population in suspension. If there is no residual fermentable sugar left, sugar, or wort or both may be added in a process known as priming. The resulting fermentation generates CO2 that is trapped in the bottle, remaining in solution, and providing natural carbonation. Bottle-conditioned beers may be either filled unfiltered direct from the fermentation or conditioning tank, or filtered and then reseeded with yeast
Cask ale (or cask-conditioned beer) is unfiltered, unpasteurised beer that is conditioned by a secondary fermentation in a metal, plastic, or wooden cask. It is dispensed from the cask by being either poured from a tap by gravity, or pumped up from a cellar via a beer engine (hand pump) Sometimes a cask breather is used to keep the beer fresh by allowing carbon dioxide to replace oxygen as the beer is drawn off the cask Until 2018, the Campaign for Real Ale (CAMRA) defined real ale as beer “served without the use of extraneous carbon dioxide”, which would disallow the use of a cask breather a policy which was reversed in April 2018 to allow beer served with the use of cask breathers to meet its definition of real a
Barrel-ageing (US: Barrel aging) is the process of ageing beer in wooden barrels to achieve a variety of effects in the final product. Sour beers such as lambics are fully fermented in wood, while other beers are aged in barrels which were previously used for maturing wines or spirits. In 2016 “Craft Beer and Brewing” wrote: “Barrel-aged beers are so trendy that nearly every taphouse and beer store have a section of them