Trub, from the German word meaning “sediment,” is a collective term covering sediments formed in the brewing process during wort boiling—called hot break—and upon cooling the wort before primary fermentation boiling—called cold break—as well as during cold storage of fermented beer, which is called cold trub. These three types of sediments are collectively called “trub” because they mainly consist of the same type of chemical complexes formed by the reaction between the naturally occurring polyphenols in the wort and parts of the soluble protein.
Trub, regardless of whether it is warm or cold, is a waste product that is discarded with the brewery by-products. The hot break settles along with hop residues and smaller malt particles as so-called hot trub after the wort separation process (normally a whirlpooling process; alternatively centrifugation). The cold break formed at wort cooling will, if not intentionally removed in a separate process step before fermentation, settle in the fermenting vessel along with the yeast after fermentation, and the cold trub formed during cold storage will, along with dead and settled yeast, be removed as well. The desirability of having cold break carried over into fermentation has been debated by brewers for many decades. Traditional German pilsner brewers often remove it for flavor and taste reasons, whereas other brewers claim that the cold trub is flavor neutral, but that its presence speeds up fermentation.
Formation of trub is in any case highly desirable, and thus the brewer seeks to optimize the processes with respect to maximum trub formation. It is important to remove as much as possible of the two main trub components—the polyphenols and the soluble proteins—during the brewing process because over time they will inevitably react to form insoluble complexes, giving rise to the formation of visible haze and/or precipitates in the beer. This may not present a problem in bottle-conditioned beers, but it is usually considered a flaw in pale, filtered beers, which both the brewer and the consumer may expect to be bright and clear.