Traceability of food products to their sources is critical for quick responses to a food emergency. US law now requires stakeholders in the agri-food supply chain to support traceability by tracking food materials they acquire and sell. However, having complete and consistent information needed to quickly investigate sources and identify affected material has proven difficult. There are multiple reasons that makes food traceability a challenging task including diversity of stakeholders and their lexicons, standards, tools and methods; unwillingness to expose information of internal operations; lack of a common understanding of steps in a supply chain; and incompleteness of data. Ontologies can address the traceability challenge by creating a shared understanding of the traceability model across stakeholders in a food supply chain. They can also support semantic mediation, data integration, and data exploration. This paper reports an on ongoing effort aimed at developing a formal ontology for supply chain traceability using use cases and data from partners in the bulk grain domain. The developed ontology was validated in VocBench environment through creating RDF triples from real datasets and executing SPARQL queries corresponding to predefined competency questions.