This document gives guidelines for using infrared spectrometry in in-line and on-line applications for dairy processing. These applications are distinct to those covered in ISO 21543 | IDF 201. It is applicable, but not limited, to: - the determination of protein, fat and total solids in liquid milk and milk products using mid and near infrared spectrometry; - the determination of protein, fat and moisture in solid or semi-solid products, such as milk powder, and butter and liquid dairy streams using near infrared spectrometry.