Abstract: The invention relates to a bioreactor with immobilized lactic acid bacteria which is characterized in that the bacteria are fixed on the surface of a substantially non-compressible carrier which is composed of a continuous, porous matrix or of dimpled or reticular porous particles, the matrix or the particles having a structure of a loosely associated plurality of microparticles or microfibers which are bound together chemically, adhesively or mechanically at least at some contact points between the individual microparticles or microfibers. Preferably the microparticles or microfibers comprise or consist of a material, preferably a resin, having anion exchanger capability. A preferred embodiment of the carrier includes DEAE-cellulose, the microparticles and microfibers being agglomerated with polystyrene.