Flocculation Mechanisms of Top and Bottom Fermenting Brewing Yeast

Abstract

The flocculation behaviour of a large set of top and bottom fermenting brewing yeasts was investi gated. Bottom and top fermenting strains flocculated according to different mechanisms. Bottom strains flocculated in the stationary growth phase in the presence of sufficiently high Ca2+ and suffi ciently low sugar concentrations; these strains possessed a lectin-mediated flocculation mechanism.Top strains flocculated in the stationary growth phase without addition of Ca2+, only in the presence of sufficiently high concentrations of ethanol. Some of the top strains were inhibited with mannose, but not with sucrose or galactose, while others were not inhibited by any of these sugars. The different sensitivity of flocculation of top and bottom strains with respect to ethanol may be related to the hydrophobicity of the cell surface. Flocculation models for bottom and top fermenting yeasts were proposed. It is suggested that, besides the sugar inhibition pattern, the sensitivity of flocculation with respect to ethanol should be included as an additional parameter for classification of brewing yeasts.

Carbohydrate carbon sources induce loss of flocculation of an ale-brewing yeast strain

“…Four phenotypes were described taking into account pH and sugar inhibition sensitiveness or the requirement of ethanol to induce flocculation, they were: Flo1 phenotype, the flocculation of these strains was only inhibited by mannose; NewFlo phenotype, inhibited by mannose and glucose; mannose insensitive (MI) phenotype and ethanol‐dependent flocculation (Stratford and Assinder 1991; Masy et al. 1992b; Dengis and Rouxhet 1997). The majority of brewery yeasts belong to NewFlo phenotype (Stratford and Assinder 1991), which flocculates in the stationary phase of growth, while almost all Flo1 phenotype strains are constitutively flocculent (Stratford and Assinder 1991; Stratford and Carter 1993; Soares and Mota 1996).…”

Flocculation in Saccharomyces Cerevisiae

“…Flocculation of the majority of brewing strains is not affected by ethanol ( Stratford, 1992c ); for some strains, where fl occulation mechanism is most likely different from the lectin-like model, fl occulation increases with ethanol concentration or only occurs in the presence of ethanol ( Mill, 1964b ;Dengis et al , 1995 ;Dengis and Rouxhet, 1997 ). Conversely, a negative effect of ethanol in yeast fl occulation was reported ( Kamada and Murata, 1984 ).…”

“…However, no clear relationship between electrical properties and the onset of fl occulation was found ( Amory et al , 1988 ;Dengis et al , 1995 ;Dengis and Rouxhet, 1997 ).…”

“…For instance, CSH and more recently the presence of 3-hydroxy fatty acids (3-OH oxylipins) on yeast cell wall has been positively correlated with the onset of fl occulation ( Straver et al , 1993 ;Jin et al , 2001 ;Strauss et al , 2005 ). However, other authors described no signifi cant differences in CSH or surface concentrations of proteins, polysaccharides or hydrocarbons between fl occulent and non-fl occulent cells at stationary and exponential phases of growth, respectively ( Dengis et al , 1995 ;Dengis and Rouxhet, 1997 ).…”

“…Later on, two other phenotypes have been described: MI phenotype, composed by strains where fl occulation is not inhibited by sugars, including mannose ( Masy et al , 1992 ), and a fourth phenotype, comprising strains whose fl occulation occurs in the presence of suffi ciently high ethanol concentration ( Dengis et al , 1995 ;Dengis and Rouxhet, 1997 ). The exact mechanism of aggregation of these strains is far from being understood.…”