Circle Fermenter, conceived by Arianna Bosco, Matteo Cappellari, Vincenzo Cassano, Elena Gasparrini, and Qianhuai Zeng, is an open-source modular fermenter that allows experimenting with new processes and techniques related to the self-production of fermented foods. Exploiting the metabolic processes of fungal organisms, the project introduces new active agents into food systems, defining a scenario that explores and promotes a symbiotic collaborative relationship between humans and microorganisms, where food self-production is the result of a shared activity. Simple and economical to build, easy to configure, and versatile in its experimental use, Circle Fermenter promotes the spread of circular production processes for healthy and environmentally friendly foods.