There are three main fermentation methods, warm, cool and wild or spontaneous.
Fermentation may take place in open or closed vessels.
There may be a secondary fermentation which can take place in the brewery, in the cask or in the bottle.
In general, yeasts such as Saccharomyces cerevisiae are fermented at warm temperatures between 15 and 20 °C (59 and 68 °F), occasionally as high as 24 °C (75 °F),while the yeast used by Brasserie Dupont for saison ferments even higher at 29 C (84 F) to 35 °C (95 F).
They generally form a foam on the surface of the fermenting beer, as during the fermentation process its hydrophobic surface causes the flocs to adhere to CO2 and rise; because of this, they are often referred to as "topcropping" or "topfermenting"– though this distinction is less clear in modern brewing with the use of cylindro-conical tanks.
Generally, warmfermented beers are ready to drink within three weeks after the beginning of fermentation, although some brewers will condition them for several months.
Lager is beer that has been cool fermented at around 10C (50 F), compared to typical warm fermentation temperatures of 18 °C (64 F).
It is then stored for 30 days or longer close to the freezing point,
and during this storage sulphur components developed during fermentation dissipate.