Although much public engagement with the field of “synthetic biology” has been conducted, there remains little work that develops an appreciation of how people make sense of this field and its concomitant promised futures from within their everyday lives. Using a case study, based on the compound “menthol” (a terpenoid from plants) which synthetic biologists have developed for production in E. coli, we explore how people make sense of uncertainties in promised or feared futures. Menthol is already an ingredient in many consumer products and the pre-existing use of such products may frame people’s everyday techniques for understanding biosynthetic menthol, with implications for their appreciation of synthetic biology more generally. We adopted a range of sensory methods, including “pop-up” stalls, sketch research, object elicitation interviews and home tours, to explore the everyday situations in which menthol already figures. Participants used a range of strategies, including deferring judgment, invoking other actors as mediators, using their own bodily experiences and using existing moral repertoires, to respond to biosynthetic possibilities. We deploy the concept of “everyday uncertainty work” and show that it is a useful one for understanding how people’s everyday epistemic cultures of uncertainty are routinely adapted to the anticipation of sociotechnical uncertainties, such as those that accompany promissory accounts of science. The implications for these findings for public engagement with technoscience and uncertainty are discussed.