Lean manufacturing aims at flexible and efficient manufacturing systems by reducing waste in all forms, such as, production of defective parts, excess inventory, unnecessary processing steps, and unnecessary movements of people or materials. Recent research stresses the need to include planning systems in a lean evaluation and redesign of manufacturing systems. Lean planning systems may contribute to a regular, customer focused flow of products. In line with these ideas we study the redesign of a complex planning system for a coffee manufacturing plant. We show how simulation may be used to facilitate the engineering process, by allowing for direct participation, and contributions of planners, managers, and domain experts. More in particular we discuss, and evaluate the use of a modeling framework for manufacturing simulation. It supports conceptual modeling by offering an architecture of high-level class descriptions of manufacturing elements and relationships for specifying simulati...