Parametric and non-parametric Statistical Process Control in a dairy industry

Brazil is one of the world's largest producers of bovine milk, and much of it is destined for cheese production. In order to maintain the cheese industry, the milk, which is its main raw material, must hold a high quality. Given that the milk quality is assessed by many variables in continuous flow, the statistical process control (SPC) can be one tool to monitor them. In this paper, parametric and non-parametric control charts were used to verify if the milk receiving process in one cheese industry located in the city of Sao Luis de Montes Belos, in the state of Goias, Brazil, was under statistical control. Normality and symmetry of the data were verified and, as expected, the parametric SPC was apparently more powerful. The authors suggest the utilization of the SPC as a tool to ensure the quality in the dairy industry, but always verifying if the assumptions of each methodology are met. Specifically, if normality is verified in the data, the parametric charts are more powerful, and they are recommended for this case.