This study is framed in the social perspective of Epistemology of Science, and it aims to examine the epistemic operations performed by high school students while engaged in a role-play about food safety that requires them to engage in both argumentation and decision-making practices. The epistemic operations are examined on two different levels: 1) operations performed by each small group of students during their discussion as to how they intend to proceed in the general debate; and 2) operations performed in the general debate that prevail in students' decisions for solving the alimentary emergency. The participants are 11th grade high school students (16-17 years old). The data is examined through discourse analysis. The main findings suggest that the epistemic operations related to proposing knowledge are performed to a greater extent during the small group discussions, whereas those related to evaluating knowledge are more prevalent during the general debate. The main contribution of this work is the connections established between different areas of research, most notably the need to consider epistemic knowledge for the adequate engagement of students in the practice of argumentation as well as the use of role-playing in a socio-scientific setting to promote students' argumentative discourse.