In this investigation, the effect of hot trub (a precipitation product of the wort boiling process in beer manufacturing) addition on fermentation performance was observed under variation of yeast vitality, and origin and the amount of hot trub. Its addition improved suspended cell concentrations for all yeast vitalities tested, and the more trub was added, the greater the effect. Further, pilot-scale fermentations showed significantly lower pH values and an accelerated extract degradation, thus, advancing fermentation by roughly I day for hot trub addition versus the fermentation of extremely bright wort. Since the positive effect of trub has often been associated with its particulate characteristics, fermentations with fractionated model particles, such as poly(vinylpyrrolidones) and kieselguhr, of different particle sizes were carried out under variation of yeast vitality and particle amounts. The addition of both particle types also improved fermentation performance, however, the effect was not as great as that of hot trub. Particulate material may improve the development Of CO2 from the fermenting medium, thus reducing its concentration and inhibitory effect on yeast metabolism. The most effective fraction of kieselguhr had a 40 mu m peak which also occurred in particle size distributions of all hot trubs investigated. This could be of particular interest when discussing particle effects. (C) 2007 Elsevier Inc. All rights reserved.