Statistical tools for net quantity control in the dairy industry

Abstract

A pilot study was carried out to assist management in the development of an improved strategy for net quantity control in a medium volume, liquid milk, carton line operation. A low cost statistical quality control system was used to demonstrate that computerization for net quantity data handling and interpretation must be part of an improved strategy to prove compliance with weights and measures legislation. A process capability study identified differential behaviour between filling valve sets which required an improved maintenance plan in order to prevent process instability when filling one litre cartons. Preliminary and ongoing process capability indices for skimmed, semi‐skimmed and whole milk in half pint and one pint cartons were two to four times the minimum required to prove capability. Overfill was typically of the order 0.2 to 0.4% of the nominal quantity for half pint and one pint fills, but it tended to be higher for whole milk due to an overestimation of the milk density. Overfill on the one litre carton was shown to be excessive at 0.8% of the nominal quantity.