Wort Boiling Method

After mashing, the beer wort is boiled with hops (and other flavourings if used) in a large tank known as a "copper" or brew kettle – though historically the mash vessel was used and is still in some small breweries.
The boiling process is where chemical reactions take place, including sterilization of the wort to remove unwanted bacteria, releasing of hop flavours, bitterness and aroma compounds through isomerization, stopping of enzymatic processes, precipitation of proteins, and concentration of the wort.
Finally, the vapours produced during the boil volatilise off-flavours, including dimethyl sulfide precursors.
The boil is conducted so that it is even and intense – a continuous "rolling boil".
The boil on average lasts between 45 and 90 minutes, depending on its intensity, the hop addition schedule, and volume of water the brewer expects to evaporate.
At the end of the boil, solid particles in the hopped wort are separated out, usually in a vessel called a "whirlpool".

Brew kettle or copper

Brew kettles at Brasserie La Choulette in France
Copper is the traditional material for the boiling vessel, because copper transfers heat quickly and evenly, and because the bubbles produced during boiling, and which would act as an insulator against the heat, do not cling to the surface of copper, so the wort is heated in a consistent manner.

The simplest boil kettles are direct-fired, with a burner underneath.
These can produce a vigorous and favourable boil, but are also apt to scorch the wort where the flame touches the kettle, causing caramelisation and making cleanup difficult.

Most breweries use a steam-fired kettle, which uses steam jackets in the kettle to boil the wort.
Breweries usually have a boiling unit either inside or outside of the kettle, usually a tall, thin cylinder with vertical tubes, called a calandria, through which wort is pumped.