This paper focuses on the knowledge representation task for an interdisciplinary project called Delicious concerning the production and transformation processes in food science. The originality of this project is to combine data from different disciplines like food composition, food structure, sensorial perception and nutrition. Available data sets are described using different vocabularies and are stored in different formats. Therefore there is a need to define an ontology, called PO2 (Process and Observation Ontology), as a common and standardized vocabulary for this project. The scenario 6 of the NeON methodology was used for building PO2 and the core component is implemented in OWL. By making use of PO2, data from the project were structured and an use case is presented here. PO2 aims to play a key role as the representation layer of the querying and simulation systems of Delicious project.