Crop growth models help to formalize expert knowledge to assess and design cropping systems with multiple criteria (i.e. production and externalities). The process of modelling to develop an operational tool requires different skills from conceptualization of the biophysical system to the coding of the equations. The focus of this paper is on the procedure to develop a new crop model from an existing one, using a crop modelling framework. First, the conceptual model is co-developed by scientists of different backgrounds, having theoretical and/or practical knowledge of the crop. Then, to translate the conceptual model into an operational tool, there is a need for communication between these experts and software engineers coding the model. We illustrate the approach with a case study of changing a wheat crop model into a pea model.