Miso fermented in space has a unique flavor

The ancient culinary practice of fermentation may play a role in the future of space cuisine.

In March 2020, an interdisciplinary team of researchers sent a small batch of ingredients for the Japanese condiment miso to the International Space Station (ISS). In the first experiment of its kind, the miso spent 30 days fermenting aboard the orbiting laboratory and was flown back to Earth for more analysis — including taste tests.

Study participants discovered that the batch fermented in orbit had the characteristic savory flavor of miso, but tasted noticeably nuttier then identical batches that had remained on Earth to ferment. There were also differences in the microbial and chemical profiles, the researchers found.

In a paper published in iScience on April 2, the team reports they can’t be sure what exactly caused the differences. But, they say, it demonstrates that fermenting food in space is feasible — and that could lead to healthier, tastier food for astronauts.

A new frontier for fermentation

The “space miso” project was started by Maggie Coblentz, a researcher at the MIT Space Exploration Initiative and co-lead author of the study. “I was thinking about expanding food products for astronauts beyond the freeze-dried military ration style,” she said.

Fermentation emerged as a possible avenue when Coblentz began collaborating with food researcher Josh Evans of the Technical University of Denmark. They wondered whether fermenting foods in space could provide a way of bringing more flavor, microbial diversity, and nutritional value to the astronaut diet.

On Earth, demand for fermented foods and beverages is growing, from kimchi to kombucha, driven in part by interest in their contributions to gut health and sustainable food practices.

But little was known about how fermentation would work in space. Experiments performed in labs on Earth had suggested that microgravity could alter the process. But fermentation on the ISS had not been attempted before.

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When an opportunity to send an experiment to space came up, the team chose to send fermenting miso for a few reasons.

The first was practical, says Evans. As a paste, miso is less likely to leak than fermented beverages, reducing the risk of damaging other experiments and equipment on the ISS. And the process of fermentation for miso was a good fit for the 30-day window they had available for the experiment.

There were scientific considerations as well, adds Evans, who studies how different ecosystems of microbes influence the flavor of fermented foods. A recent surge of research about miso fermentation allowed the team to compare their space-fermented miso and put their results into context.

Then there were the culinary reasons: Used in soups, sauces, and marinades, miso is nutritious, has a strong umami flavor, and a rich cultural history.

Bringing fermentation to space

Miso is made from cooked soybeans, salt, and koji — a fermentation starter made of a grain like rice or barley that has been inoculated with a fungus called Aspergillus oryzae.

“The overall process has two main steps,” Evans said. “First you grow the koji, which needs air. Then when you mix the ingredients and pack the mixture into the fermentation container, the salt and lack of oxygen kills the koji and lets bacteria and salt-tolerant yeast take over to continue the fermentation.” 

Those bacteria break down the sugars in the starting mixture into other compounds, including those that give miso its savory flavor. The specific flavor of a miso can vary based on a batch’s unique microbial culture, as well as a variety of environmental factors that could be different in space.

For the experiment, the team in Denmark prepared a batch of miso of around 2 pounds (1 kilogram), and divided it into three portions. In March of 2020, one portion went up to the ISS for 30 days, one went to Coblentz in Massachusetts, and one stayed in Denmark with Evans.

To monitor the space environment, Coblentz and Evans brought engineers and food scientists onto the team. They built what they called “sensing boxes” for the miso portions that went to space and stayed in Massachusetts. The boxes recorded temperature, humidity, pressure, and radiation in the environment throughout the 30-day fermentation process.

All three batches were frozen before and after the 30-day experiment window to minimize the differences between batches.

Taste tests

The space miso was not consumed onboard the ISS. But by working to identify potential challenges or safety issues involving fermented foods in space, the team hoped to bring them a step closer to the ISS menu.

When the team analyzed the microbial cultures of the misos back in Evans’ lab, they found that the three miso microbial communities were similar and had most species in common, almost all coming from the Staphylococcus genus. However, only the miso fermented on the ISS contained a species known as Bacillus velezensis, which had been identified previously in fermented soy foods. The authors think this may have been because the temperature inside the sensing box onboard the ISS unexpectedly rose to 97.3 degrees Fahrenheit (36.3 degrees Celsius) — compared to the portions on Earth, which were kept at between 68 and 77 F (20 to 25 C).

The different misos also had differences in aroma and flavor. A group of 14 panelists that the team assembled described the space miso as having a nutty, roasted aroma and a stronger umami taste compared to the two Earth misos. 

These differences may have been reflected in the chemical compounds found in the misos. The space miso contained higher concentrations of compounds with cheese-like flavors (2-methylbutanoic acid) and honey-like flavors (methyl phenylacetate).

Future frontiers

While the authors of the study concluded that miso could be fermented in space, they are not sure how or whether factors like microgravity and radiation affected the fermenting miso’s specific properties. Then there was the unwanted heat that reached the miso, plus a bumpy ride with high g-forces to and from orbit, and other environmental differences.

“All we can say is it’s different there than it is here. But there’s so many reasons why that could be, and probably it’s all those things working together,” Coblentz said.

Researchers want to understand how those factors altered the miso before astronauts actually start fermenting their own ingredients. Astronauts’ food supplies are tightly controlled because the risks of getting sick in space are much higher than on Earth. For instance, when kimchi was flown to the ISS in 2008, it was blasted with radiation before flight to kill bacteria and prevent the cabbage from continuing to ferment onboard. The unexpected change in the miso’s temperature shows that the fermentation process wasn’t kept under perfect control — something that would need to be addressed when bringing fermented food to the ISS.

Fermentation is a process that is naturally sensitive to changes in its environment, notes Andrew MacIntosh, a fermentation expert at the University of Florida who was not involved in the study. “Space opens up a whole new avenue,” he said. “And a lot of the value that we see in this paper is the difficulties that these researchers went through trying to glean information about how space would be different.”

MacIntosh sees this as a step toward a possible future in which space exploration could be more self-sustaining and less dependent on deliveries from Earth. Microbial communities involved in fermentation could be harnessed and engineered to produce ingredients for foods and even pharmaceuticals, he thinks.

Coblentz says their work could also help make space more welcoming for travelers by offering more choices for food, whether through producing it via fermentation or simply enhancing its flavor. “Drawing upon our deep earthly history of working with food and fermentation across different cultures around the world — it has sort of a poetic aspect to it,” she said.