The boiling of wort can be carried out in several ways: either through direct heating with a flame beneath the boiling vessel or by steam injection using internal or external calandrias. The choice of heating method depends on the brewer’s preference.

At this stage, hops are also added. Their compounds undergo chemical transformations due to the heat. Clarifying agents such as kappa-carrageenans are also introduced, forming a mesh that traps proteins and allows them to be more easily removed from the wort by sedimentation after boiling.

The reasons for boiling are:

Extraction of resins from the hops.
Isomerization of humulone into soluble isohumulone.
Evaporation of most — but not all — volatile hop oils.
Termination of any possible enzymatic activity.
Sterilization of the wort.
Concentration of the wort.
Removal of raw malt grain odors.
Development of a darker color in the wort.

At the end of the boiling process, the wort is filtered to remove hop leaves if whole hops were used. Otherwise, it is transferred directly into large vessels where it remains undisturbed for 20 to 30 minutes, allowing sediment composed of resins, proteins, and tannins to settle.

The now-clear wort is then passed through heat exchangers and cooled to 6–10°C, the appropriate temperature for fermentation. Immediately afterward, it is aerated to create an ideal environment for yeast growth.