The operability and flexibility of an existing milk treatment process are investigated through flowsheet modelling and simulation. From the flowsheet simulation, a process operating region was determined using incoming milk flow viscosity and heat exchanger pressure drop as characteristic parameters. The operability and flexibility of the nominal operating points were evaluated with a minimization of the process pasteurization and cooling temp. through vertex enumeration. The simulation procedure provides a quantitative method for developing a flexible process in dairy industry applications. The established process operability and flexibility analysis framework and and flowsheet simulation can be adapted to other liquid food productions.