Abstract: In a milking machine teat cup wherein an animal to be milked has its teat inserted into a teat cup liner during milking, a first electrode extends about or within at least a portion of the teat cup liner. To clean and/or disinfect the liner, a second electrode is inserted into the liner and the two electrodes are charged so as to generate plasma in any free space between the inserted second electrode and the interior surface of the liner. The generated plasma species destroy organisms that cause mastitis, and can additionally kill other unwanted organisms and/or perform cleaning of the liner's interior.