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Cell immobilisation is the physical restriction of cells in a delimited region by means of physical and chemical approaches. It usually comprises a solid support containing cell biomass. In brewing fermentations, yeast cell immobilisation was widely explored during the 1970s to the 90s, with the expectation that immobilised systems would revolutionise the brewing industry. The most studied immobilisation method has been the attachment to a surface and entrapment within a porous solid. Some industrial applications were developed, but the flavour profile of the product rarely matched that produced by batch fermentation. Numerous factors are important in immobilised yeast systems and its successful industrial implementation. Although cell immobilisation results in many advantages, such as high biomass loading and ease of cell reuse, there are drawbacks including physiological changes and mass transfer limitations. Therefore, in order to design a feasible brewing fermentation process using immobilised yeast cells, the solid support, immobilisation method and the bioreactor system require to be properly developed. In this review, yeast cell immobilisation technology in brewing is considered together with methods of immobilisation with the associated advantages and drawbacks. Physiological and metabolic alterations in yeast are also explored and industrial applications are highlighted. It is suggested that immobilisation technology has new opportunities as the market is increasingly open to novel flavours and styles.

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There is an ever-increasing demand for reduction of unit operations and a growing interest in the physiology of yeasts used in beer fermentation. In this context, cell immobilization is an interesting alternative, since it reduces steps to separate biomass from fermented broth. Yet, physiological alterations in yeast metabolism caused by immobilization are still to be fully described. Thus, the main objective of this work was to evaluate the physiology of three brewer's S. cerevisiae yeast strains (SY025, SY067 and SY001) immobilized on a porous cellulose-based support. Batch fermentations in malt extract 12 degree P were carried out for all strains both in free and immobilized forms in order to compare kinetic parameters obtained from distinct process conditions. Mathematical modeling was performed following two viewpoints: modeling of fermentation kinetics by parameter estimation from experimental data and application of a reaction-diffusion model for estimation of substrate concentration gradient inside the immobilization support. Moreover, fermentations with different initial substrate and biomass concentrations were carried out using strain SY025, aiming to evaluate their influence over flavor compounds, using statistical models. Compared to free cells, immobilized yeasts showed both higher glycerol yield (SY025, 40%; SY067, 53%; SY001, 19%) and biomass yield in the system (SY025, 67%; SY067, 78%; SY001, 56%). On the other hand, free cells presented higher ethanol yields when compared to immobilized ones (SY025, 9%; SY067, 9%; and SY001, 13%). According to the model developed, a substrate gradient inside the support was predicted, but with low mass transfer limitations.