The aim of the present study was to test the use of thermally dried immobilized kefir co-culture on casein as a biocatalyst. The impact of repeated batch fermentations and the effect of storage of the dry biocatalyst on cell viability and fermentative activity were investigated. Kefir casein-supported biocatalyst was used in repeated batch fermentations at various temperatures. The high number of repeated batch fermentations showed a tendency for high operational stability of both wet and thermally dried kefir casein-supported biocatalyst. Fermentations continued for up to 2 months without any significant loss of fermentative activity. Subsequently, the effect of air Circulation, drying temperature, and the effect of storage on viability and fermentation efficiency of thermally dried immobilized and free kefir co-culture were studied. Survival rates up to 94% were reported and remained high, even after storage for 365 days. Reactivation after storage was immediate and lactic acid content up to 43.1 g/L was detected, while ethanol concentration and daily ethanol productivity ranged 0.3-1.4% vol and 0.4-2.7 g/L, respectively in whey fermentations with thermally dried immobilized biocatalyst. The potential of thermally dried immobilized kefir co-culture on casein as a starter in a series of food industrial applications is evaluated. (c) 2008 Elsevier Ltd. All rights reserved.