Lactobacillus rhamnosus cells were encapsulated in alginate/starch liquid-core capsules and cultured in a whey-based growth medium supplemented with yeast extract, Tryptone, and calcium carbonate to enable concentrated biomass production in an immobilized matrix without centrifugation or filtration. The characteristics of the encapsulated cell culture were compared with those of freely suspended cell fermentation under the same bioreactor conditions. The population of encapsulated viable cells reached a concentration of 4.8 x 10(10) cfu cm(-3) of capsule volume, while the population of free cells cultured at the same conditions during control fermentation was 5.7 x 10(9) cfu cm(-3) Of growth medium. Despite the higher cell concentration in the capsules, the overall cell productivity of encapsulated culture was lower than that obtained in free-cell fermentation. The effects of lactic acid inhibition on cell growth in the capsules caused by mass transfer limitations were evidenced by premature growth cessation and earlier uncoupling between growth and acid production as compared to free-cell culture. The capsules remained stable and no cell release was observed during 60 h of fermentation.