Cleaning and characterization of stainless steel exposed to milk

Abstract

Cleanliness criteria for a milk-stainless steel interface system were established by monitoring the elemental composition of the stainless steel surface by Auger electron spectroscopy. A reproducible chemical cleaning procedure to remove milk deposits from the surface was designed. If UV-ozone exposure of the chemically cleaned surface was included as a last step in the cleaning procedure, the amount of contaminants (as carbon) present at the surface was further reduced. Argon sputtering of the surface showed that the contaminants were confined to a surface layer 5 nm thick of the stainless steel plate. Chemically cleaned plates could be stored in Petri dishes in a desiccator for up to 56 days without significant recontamination as measured by the carbon content on the surfaces. However, storage in air resulted in gross recontamination of the surface within a few hours. Scanning and transmission electron microscopy were used to examine the surfaces of cleaned stainless steel plates and the topography of milk deposits attached to the plates. Preparation procedures for these special applications were developed.