Stability of high cell density brewery fermentations during serial repitching.
The volumetric productivity of the beer fermentation process can be increased by using a higher pitching rate (i.e. higher inoculum size). However, the decreased yeast net growth observed in these high cell density brewery fermentations can adversely affect the physiological stability throughout subsequent yeast generations. Therefore, different O(2) conditions (wort aeration and yeast preoxygenation) were applied to high cell density fermentation and eight generations of fermentations were evaluated together with conventional fermentations. Freshly propagated high cell density populations adapted faster to the fermentative conditions than normal cell density populations. Preoxygenating the yeast was essential for the yeast physiological and beer flavor compound stability of high cell density fermentations during serial repitching. In contrast, the use of non-preoxygenated yeast resulted in inadequate growth which caused (1) insufficient yield of biomass to repitch all eight generations, (2) a 10% decrease in viability, (3) a moderate increase of yeast age, (4) and a dramatic increase of the unwanted flavor compounds acetaldehyde and total diacetyl during the sequence of fermentations. Therefore, to achieve sustainable high cell density fermentations throughout the economical valuable process of serial repitching, adequate yeast growth is essential.
Verbelen
Pieter J
PJ
The Centre for Malting and Brewing Science, Faculty of Bioscience Engineering, Katholieke Universiteit Leuven, Kasteelpark Arenberg 22, Box 2463, 3001, Heverlee, Belgium. Pieter.Verbelen@biw.kuleuven.be
Dekoninck
Tinne M L
TM
Van Mulders
Sebastiaan E
SE
Saerens
Sofie M G
SM
Delvaux
Filip
F
Delvaux
Freddy R
FR
D001515:Beer / Q000382:microbiology*; D001709:Biotechnology / Q000379:methods*; D005227:Fatty Acids / Q000032:analysis; D005285:Fermentation; D005421:Flavoring Agents / Q000032:analysis; D006003:Glycogen / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000166:cytology* / Q000254:growth & development / Q000502:physiology; D013997:Time Factors; D014199:Trehalose / Q000378:metabolism
D005227:Fatty Acids; D005421:Flavoring Agents; D006003:Glycogen; D014199:Trehalose