The complexity of the transition to more sustainable food systems has taken multiple trajectories, differently driven and oriented. In this scenario, innovation pathways promoted at the grassroots level and based on collective action driven by social purposes appear to carry a strong transformative capacity. Considered as expressions of social innovation, their study has been approached through different theoretical frameworks. By referring to some of these, and in particular to the developments of transition theories, we analyse the innovation pathways involving the wheat-bread value chain in Tuscany (Italy). The analysis sheds light on the relevance of the nature of social innovation carried out by grassroots initiatives in their pursuing radical change aimed at deeply redefining production-consumption practices through social interaction, to meet socially shared needs and achieving several social benefits. The paper also analyses the factors and mechanisms underlying the change processes this innovation has triggered in the mainstream system, focusing on the so-called “anchoring” process. Through this analysis, the work aims at improving the understanding of the transformative potential of social innovation.