In this case study, students assume the role of a process engineer on a whey refinement process.  As the process engineer for the line, students must develop a block diagram of the process, perform a mass balance on each step of the process, and determine any discrepancies between the flow rates they have determined in their mass balances and the theoretical flow rates based on clean, fully-functioning equipment.  Students are asked to develop reasons for any flow rate discrepancies found.  This scenario is commonly found in industry, as mass balances are routinely used to determine the presence of leaks, the need for cleaning, or faulty equipment. This case study was developed for an upper-level undergraduate food engineering course. It is appropriate for food engineering, food processing, and introductory mass balance courses.