Penicillium has been used to immobilize Saccharomyces cerevisiae in the absence of physico-chemical external supports. The technique consists in reproducing conditions that are adequate for a forced symbiosis: a carbon source (gluconic acid) that can only be used by the filamentous fungus, buffered medium, and constant agitation. In this way, we obtained hollow spheres containing both microorganisms that were named "yeast biocapsules". Repeated batch fermentation using yeast biocapsules were successfully carried out for at least seven times without any significant loss in ethanol production from molasses. The effects on must fermentation development and concentrations of by-products have been also studied. Only acetaldehyde, isobutanol, ethyl acetate and acetoin showed significant differences (p <= 0.05) when free and immobilized cells were compared. Lastly direct fermentation of starch to ethanol using this new immobilization system was also investigated. Additional potential applications of yeast biocapsules for biotechnological processes are proposed in this paper. (c) 2006 Elsevier Inc. All rights reserved.