When rubber equipment in a milking system ages, physical and chemical deterioration occurs and cracks, crevices, as well as deposits of organic and inorganic material is formed on the surface. Bacterial colonization can accumulate, especially on ageing rubber equipment and if the cleaning procedure is not functioning properly. Formation of biofilm in milking equipment could in turn cause bacterial contamination of bulk tank milk. ATP bioluminescence is a fast and easy way to determine the hygienic status of a surface based on its ATP content, and results are given in relative light units (RLU). The method measures both bacterial contamination as well as residues from other organic material.