A method for operating a pasteurizing device for pasteurizing foods filled into sealed containers, comprising transporting containers which are filled with foods and sealed through multiple treatment zones in a transport direction by means of a transport means, treating the foods in the treatment zones by applying a tempered, aqueous treatment liquid to an exterior of the containers, wherein treatment liquid with a specific temperature is supplied to each treatment zone via a feed pipe, such that the foods are pre-heated, in transport direction, in at least one warm-up zone (10, 11), heated, following in transport direction, to pasteurizing temperature in at least one pasteurizing zone, and cooled down, following in transport direction, in at least one cool-down zone (13, 14), and wherein the treatment liquid is collected in the treatment zones after application to the containers, and collected treatment liquid is re-supplied to at least one treatment zone for reuse via circulation circuit pipes of a circulation circuit, and wherein a partial quantity of treatment liquid is continuously removed from the treatment liquid circulated in the circulation circuit or from the treatment liquid in a treatment zone by means of at least one liquid-removal means for forming at least one partial flow of the treatment liquid, which at least one partial flow is supplied, via a feeding pipe of at least one bypass, to a membrane filtration means arranged in the at least one bypass and filtered, and subsequently fed back again into the circulation circuit or into a treatment zone, and wherein process chemicals are added to the treatment liquid, characterized in that a biocide, selected from a group consisting of hypochlorite, peracetic acid, chlorine dioxide and bronopol, or a mixture of biocides selected from this group, is apportioned to the treatment liquid as process chemical, such that a concentration of the biocide, or a total concentration of biocides, does not exceed 0.4 mmol/L, and that a pH-regulating agent comprising at least one inorganic or organic acid is apportioned to the treatment liquid as process chemical, such that a pH value of the treatment liquid is set to a range from 3.5 to 7.0. transporting containers which are filled with foods and sealed through multiple treatment zones in a transport direction by means of a transport means, treating the foods in the treatment zones by applying a tempered, aqueous treatment liquid to an exterior of the containers, wherein treatment liquid with a specific temperature is supplied to each treatment zone via a feed pipe, such that the foods are pre-heated, in transport direction, in at least one warm-up zone (10, 11), heated, following in transport direction, to pasteurizing temperature in at least one pasteurizing zone, and cooled down, following in transport direction, in at least one cool-down zone (13, 14), and wherein the treatment liquid is collected in the treatment zones after application to the containers, and collected treatment liquid is re-supplied to at least one treatment zone for reuse via circulation circuit pipes of a circulation circuit, and wherein a partial quantity of treatment liquid is continuously removed from the treatment liquid circulated in the circulation circuit or from the treatment liquid in a treatment zone by means of at least one liquid-removal means for forming at least one partial flow of the treatment liquid, which at least one partial flow is supplied, via a feeding pipe of at least one bypass, to a membrane filtration means arranged in the at least one bypass and filtered, and subsequently fed back again into the circulation circuit or into a treatment zone, and wherein process chemicals are added to the treatment liquid, characterized in that a biocide, selected from a group consisting of hypochlorite, peracetic acid, chlorine dioxide and bronopol, or a mixture of biocides selected from this group, is apportioned to the treatment liquid as process chemical, such that a concentration of the biocide, or a total concentration of biocides, does not exceed 0.4 mmol/L, and that a pH-regulating agent comprising at least one inorganic or organic acid is apportioned to the treatment liquid as process chemical, such that a pH value of the treatment liquid is set to a range from 3.5 to 7.0.