Brewing - Conditioning

Conditioning

After initial or primary fermentation, the beer is now 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 type of 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 acetylaldehydes.

Kräusening

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.

Lagering

Lagers are aged at near freezing temperatures for 1–6 months depending on style. This cold aging serves to reduce sulphur compounds produced by the bottom-fermenting yeast and to produce a cleaner tasting final product with fewer esters. Unpleasant flavours such as phenolic compounds become insoluble in the cold beer, and the beer's flavour becomes smoother. During this time pressure is maintained on the tanks to prevent the beer from going flat. If the fermentation tanks have cooling jackets on them, as opposed to the whole fermentation cellar being cooled, conditioning can take place in the same tank as fermentation. Otherwise separate tanks (in a separate cellar) must be employed. This is where aging occurs.

Secondary fermentation

During secondary fermentation, most of the remaining yeast will settle to the bottom of the second fermenter, yielding a less hazy product.

Bottle fermentation

Some beers undergo a fermentation in the bottle, giving natural carbonation. This may be a second or third fermentation. They are bottled with a viable yeast population in suspension. If there is no residual fermentable sugar left, sugar may be added. The resulting fermentation generates CO₂ that is trapped in the bottle, remaining in solution and providing natural carbonation.

Cask conditioning

Cask ale or cask-conditioned beer is the term for unfiltered and unpasteurised beer that is conditioned (including secondary fermentation) and served from a cask without additional nitrogen or carbon dioxide pressure.