Miso fermented on the International Space Station is out of this world

For the first time, fermentation has been achieved in space. Miso made aboard the International Space Station (ISS) aged faster than the controls kept on Earth and contained more fungal mutations.

Miso is a Japanese condiment made by fermenting cooked soybeans, kōji (a starter culture containing the fungus Aspergillus oryzae) and salt. Similar to other fermented foods like sourdough, misos also contain microbes that originate from the environment in which they’re made, and the people who make them. As such, misos can be said to have a terroir, a term originating in winemaking that can be likened to a ‘taste of a place’, or in this case, a ‘taste of space’.

Orbiting about 400km above the Earth, the ISS’s environment is unique thanks to its microgravity and increased radiation exposure, as well as by the multinational astronauts that visit it, bringing unique microbiomes with them. While fermented foods have been taken to the ISS before, fermentation hasn’t been done in space until now.

An international team of researchers prepared a miso precursor in Copenhagen, Denmark and divided it into three portions. One sample stayed there and the other two were placed in environmental sensing boxes, which measured temperature, relative humidity, pressure, off-gassing, light and radiation and sent to Cambridge, US, and the ISS. After 30 days in low Earth orbit, the space miso was returned and all three pastes underwent metagenomic, metabolomic and sensory analysis.

On average, the space-aged miso experienced temperatures roughly 13 and 16°C higher than the Cambridge and Copenhagen misos respectively, accelerating its fermentation. The mean concentration of aroma compounds was highest in the ISS miso, which had levels of esters up to 30 times higher and pyrazines six times higher than its earthly counterparts. The higher pyrazine content, which imparted a roasted, nutty flavour, likely resulted from Maillard reactions which are accelerated by heat. While all three misos featured glutamate, known for imparting an umami taste, the ISS miso showed higher levels of asparagine and lower levels of histidine, both indicators of maturity.

Although all three miso samples contained different proportions of microbe species, pathogenic species were found only in the top portions of the misos. Traditionally, the top layer of miso is discarded before eating, as was done for these samples prior to taste tests. Genetic analysis found a greater number of Aspergillus oryzae variants in the space paste – likely due to the increased radiation levels on board the ISS.

In double-blind taste tests, all three misos were enjoyable, but the Copenhagen miso was the favourite. The earth-fermented misos, however, were associated with a ‘beany’ taste associated with underfermentation.

Miso was chosen for this space mission for several reasons. Practically speaking, a paste is less likely to leak and compromise either the experiment or sensitive ISS equipment. On top of this, with the sensory-dulling effects of space, strongly flavoured foods, especially those rich in umami, are particularly valuable to combat the ‘flavour boredom’ that plagues astronauts on long missions.