The boiling process takes sweet wort produced either by mashing or by adding extracts to water and boils it for an extended period with hops to create hopped wort. The wort is normally boiled for 1-2 hours. The hopped wort is then rapidly cooled and yeast is added for fermentation into beer. Boiling the wort is important for the following reasons:
- Boiling sterlizes the wort, killing off any bacteria and preventing infections
- Boiling hops releases critical alpha acids that bitter the beer to offset the sweetness of the malt. The longer hops are boiled, the more bitterness they will release.
- Boiling vaporizes many undesirable compounds that can cause off flavors and aromas
- Boiling causes coagulation of undesirable proteins in the wort, allowing them to fall out during cooling
Homebrewers typically boil in an open pot. The pot should be large enough to hold the entire volume of wort, plus have 10-20% additional space for foaming during the boil to avoid boiling over. Commercial brewers use more advanced boilers to enhance vaporization and reduce energy use including pressurized boilers, boiling outside the kettle (calendreias), and other external boilers.