Nowadays, fuel ethanol is both used as a substitute and an additive to the conventional fossil fuels and the interest in converting lignocellulose to fuel ethanol has expanded in the last few decades. Lignocellulose is attractive as raw material due to its high abundance and low price. However, chemical hydrolysis or pre-treatment of lignocelluloses creates several components that are toxic to fermenting organisms and makes cultivation complicated. By using encapsulated yeast, one can overcome this problem. In encapsulation, the yeast cells are confined inside a capsule composed of an outer semi-permeable membrane and an inner liquid core (Fig. 1). Encapsulation is an attractive method since it can improve the cell stability and inhibitor tolerance, increase the biomass concentration, and decrease the cost of cell recovery, recycling, downstream processing, and fermentation time. Mechanical resistance is a key parameter together with permeability for the success of an encapsulation system. In order to improve the robustness of the capsules we are testing different cross linkers to introduce covalent bonds to the chitosan-alginate matrix. By treating chitosan covered alginate capsules with glutaraldehyde the capsules became harder and less elastic. One big disadvantage in using crosslinking agent is, however, that they are toxic for the yeast. If the encapsulated yeast is treated at too harsh conditions they will die. Although, to improve the capsules mechanical strength the membrane have to be crosslinked to a satisfying degree. We have examined different capsule-treatments and found some encouraging results when applying repetitive treatments with crosslinking agent.