HCI has studied food practices and speculative food futures, and drawn on tools to support, for example, decision-making and participatory futuring in relation to food. However, there is little understanding of how quantitatively-grounded tools like interactive simulation models can mediate collaborative reasoning about large-scale food futures. This paper addresses this gap by exploring how interactive models that simulate food production can mediate how stakeholders think about and collaboratively negotiate sustainable and healthy food systems. We designed and developed an interactive crop and livestock model as a technology probe to allow UK food system stakeholders to explore the impacts of changing the configuration of the food production landscape in their region. We deployed it as part of the mediation of two workshops where stakeholders deliberated about future food systems to understand participant interactions with and experiences of it. As well as the design of the technology probe, we contribute an analysis of these workshops and present a preliminary set of guidelines for designing systems to support future thinking about food systems.