Contamination of Immobilized Yeast Bioreactors

Abstract

Microbiological contamination of immobilized yeast bioreactors for lagering of beer was studied. Four common brewery contaminants and two contaminants isolated from the continuous processing system were tested for their ability to survive and grow in the packed bed DEAE-cellulose bioreactors. Bacterial contaminants were washed out within less than six weeks without causing any alterations in the flavour composition of the beer. The initial contamination levels were lOMO6 cells ml"1. Gram positive lactic acid bacteria, Lactobacillus brevis and Pediococcus damnosus, were more persistent than a Gram negative wort bacterium, Enterobacter agglomerans.The wild yeasts Saccharomyces cerevisiae (ex. diastaticus) and Candida krusei were the most persistent contaminants and the only ones able to grow in the reactors. Another wild yeast, Rhodotorula rubra, did not survive in competition with brewer's yeast and was washed out within a few weeks. C. krusei and R. rubra were previously isolated from a spontaneously contaminated system. None of the contaminants caused formation of phenolic or other off-flavour compounds in detectable levels.

Continuous Beer Fermentation Using Immobilized Yeast Cell Bioreactor Systems

“…The continuous immobilized systems are considered by some authors more sensitive to contamination than traditional brewing systems (118), the greatest risk being the number of separate batches of wort that must be collected as feedstock to a bioreactor (119). Others report that even a fast growing contamination in wort supply need not necessarily terminate bioreactor operation when washed-out in time at short residence times (120). Nevertheless, an effective process hygiene, simple equipment design and thorough production control are essential to keep the competitiveness of continuous systems.…”

“…Factors affecting the microbiological stability of continuous immobilized cell beer fermentation systems are sterile processing, purity of yeast culture at start-up, concentration and growth rate of brewing yeast, fermentation temperature and residence time in the reactor. The growth rate of contaminants at low temperatures and their ability to adhere to brewing yeasts, carrier and reactor surface is also of great importance as regards their maintenance in the bioreactor (120,121). Wort bacteria (Pantoea agglomerans, Obescumbacterium proteus) with high specific growth rate and high dimethyl sulfide production rate were found to be the most hazardous ones during continuous primary fermentation, whereas wild yeast caused both superattenuation and formation of phenolic off-flavors (122).…”

Biofilm formation by the yeastRhodotorula mucilaginosa: process, repeatability and cell attachment in a continuous biofilm reactor

“…These systems focused on bacterial biofilm, whereas few studies with yeast cells have been performed (Busscher et al 1994). From a practical point of view yeasts are more complicated to cultivate than bacteria because of a rather slow growth and a higher susceptibility to contamination by bacteria (Saithong et al 2009) or other yeasts (Kronlof and Haikara 1991). Yeast can grow directly on plastics (Reynolds and Fink 2001) or stainless steel (Brugnoni et al 2007) but also on bacterial (Jenkinson and Douglas 2002) or fungal biofilms (Webb et al 2000) as a secondary colonizer.…”

Παραγωγη Κρασιου Και Μπυρας Με Ακινητοποιημενα Κυτταρα Σε Απολιγνινοποιημενα Κυτταρινουχα Υλικα Και Γλουτενη

“…Εγιναν είκοσι επτά επαναλαμβανόμενες ασυνεχείς παρτίδες ζύμωσης σε θερμοκρασίες 30, 20, 15, 10, 7, 5 και 0°C που διήρκεσαν τρεις μήνες χωρίς η δρα στικότητα να ελαττωθεί αλλά και χωρίς μόλυνση. Διάφοροι συγγραφείς έχουν ανα φέρει ότι διεργασίες αλκοολικής ζύμωσης με ακινητοποιημένα κύτταρα είναι ανθε κτικότερες στις μολύνσεις (CHAMPAGNE et al 1989, KRONLOF andHAIKARA 1991).…”