Effect of immobilised cell concentration on beer quality in continuous fermentation

Continuous Beer Fermentation Using Immobilized Yeast Cell Bioreactor Systems

Traditional beer fermentation and maturation processes use open fermentation and lager tanks. Although these vessels had previously been considered indispensable, during the past decades they were in many breweries replaced by large production units (cylindroconical tanks). These have proved to be successful, both providing operating advantages and ensuring the quality of the final beer. Another promising contemporary technology, namely, continuous beer fermentation using immobilized brewing yeast, by contrast, has found only a limited number of industrial applications. Continuous fermentation systems based on immobilized cell technology, albeit initially successful, were condemned to failure for several reasons. These include engineering problems (excess biomass and problems with CO(2) removal, optimization of operating conditions, clogging and channeling of the reactor), unbalanced beer flavor (altered cell physiology, cell aging), and unrealized cost advantages (carrier price, complex and unstable operation). However, recent development in reactor design and understanding of immobilized cell physiology, together with application of novel carrier materials, could provide a new stimulus to both research and application of this promising technology.

Hydrodynamic and mass transfer characteristics of three-phase gaslift bioreactor systems

This review focuses on the hydrodynamic and mass transfer characteristics of various three-phase, gaslift fluidized bioreactors. The factors affecting the mixing and volumetric mass transfer coefficient (k(L)a), such as liquid properties, solid particle properties, liquid circulation velocity, superficial gas velocity, bioreactor geometry, are reviewed and discussed. Measurement methods, modeling and empirical correlations are reviewed and compared. To the authors' knowledge, there is no 'generalized' correlation to calculate the volumetric mass transfer coefficient, instead, only 'type-specific' correlations are available in the literature. This is due to the difficulty in modeling the gaslift bioreactor, caused by the variation in geometry, fluid dynamics, and phase interactions. The most important design parameters reported in the literature are: gas hold-up, liquid circulation velocity, 'true' superficial gas velocity, mixing, shear rate, aeration rate and volumetric mass transfer coefficient, k(L)a.

Properties of hydrogel materials used for entrapment of microbial cells in production of fermented beverages

Approaches using immobilized biological materials are very promising for application in different branches of the food industry, especially in the production of fermented beverages. Materials tested by our team for the process of entrapment belong to the family of charged polysaccharides able to form beaded hydrogels by ionotropic gelation (e.g. alginate, pectate, kappa-carrageenan) and synthetic polymers (e.g. polyvinyl alcohol) forming bead- and lens-shaped hydrogels by thermal sol/gel transition. Concentration of a gel, conditions and instrumentation of gelation process, bead and size distribution, porosity, diffusion properties, mechanical, storage and operational stability, and many other parameters were followed and optimized. Our work has been oriented especially to practical applications of immobilized cells. Brewing yeast cells were successfully immobilized by entrapment materials and used in a process of batch and continual production of beer, including primary and secondary fermentation of wort. Other applications include continual production of ethanol by fermentation of different saccharide substrates (molasses, glucose syrup, wheat hydrolysate), mead and non-alcoholic beverages production.