Hot Break comprises proteins and polyphenols that coagulate during the wort boil, eventually clumping together in large enough flocs (chunks) to break out of solution and fall to the bottom of the kettle. The hot break usually occurs anywhere from 5 to 30 min after a vigorous boil has begun. Some brewers add a small amount of hops, as little as 10% of the total hop charge, to the boil at this time. This hop addition helps to precipitate the initial hot break, but it also helps suppress foaming and boilovers in the kettle. A more effective method involves adding some form of carageenan, a seaweed derivative sometimes called Irish moss, to the boil. The addition significantly enhances the clumping action of proteins and polyphenols, facilitating their removal. These “kettle finings” are most often added 10 to 20 min before the end of the boil. Once the boil is complete, brewers can use a whirlpool vessel to separate the hot break material (now, together with any hop fragments, known as trub) from the wort before transfer to the fermentation tank. It is important for whirlpooling to proceed gently because vigorous wort pumping can break up the hot break flocs, making them more difficult to remove. See whirlpool. In traditional systems using whole hop flowers, the hot break is normally removed by drawing the wort through a bed of hops, either at the bottom of the kettle or in a separate hop back vessel. The hop bed traps the flocs of trub, allowing the brewer to send clear wort to the fermenter. See hop back.

A good hot break is important for the quality of the finished beer. Excess proteins and polyphenols remaining in the wort can cause hazes and other stability problems. Among the polyphenols removed during the hot break are tannins, which, if left in the wort, can lead to both astringency on the palate and unwanted haze formation.

See also kettle finings and trub.