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Primary fermentation starts when yeast is added to the [[wort]] right after the [[boiling]] and [[cooling]] steps. Once the yeast is added, we call the mixture beer as opposed to wort. The primary, or active fermentation process typically takes 3-5 days during which the bulk of fermentable sugars are converted into alcohol and CO2. During this phase, CO2 production is strong, often producing a foamy head on the top of the beercalled [[kraeusen]].

Brewers often transfer the beer to a secondary fermenter fermentor to separate the beer from inactive yeast, proteins, tannins, hops and other products that precipitate out of the beer and form a sediment at the bottom of the primary fermenterfermentor. A secondary fermentation of 5-14 days allows fermentation to complete and also lets additional tannins, proteins and yeast to fall out of the beer. This aids in clarifying the beer and reducing sediment in the final keg or bottle.

*[http://en.wikipedia.org/wiki/Fermentation Wikipedia - Fermentation] ==Other languages==*[[:fr:Fermentation_de_la_bi%C3%A8re]]