Space exploration is expanding, which demands new technologies and enables new scientific questions. Food, as a bridge between disciplines, can bring these fundamental and applied goals together. Here, we investigate whether food fermentation in space is possible and if so, how it compares with fermentation on Earth. We fermented a miso, a traditional Japanese condiment, on the International Space Station over 30 days and compared it with two earthbound controls. Based on environmental metadata, shotgun metagenomics, whole-genome sequencing, untargeted metabolomics, colorimetry, and sensory analysis, we found that overall, the space miso is recognizable as a miso, indicating fermentation in space is possible. We also found some key microbiological and sensory differences in the space miso, which suggest distinctive features of the space environment. These findings can be harnessed to create more flavorful, nourishing foods for long-term space missions and invite further research questions across science, health, technology, and society.