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Solein (gas-fermented single-cell protein)

Solein is an industrial protein powder, not a traditional ferment. The bacterium Xanthobacter sp. SoF1 grows in a continuous gas fermentation, taking its energy from hydrogen and its carbon from carbon dioxide, and the cells are heat-inactivated and dried. The yellow powder is 68 to 73.1 % protein, depending on the conversion factor used, and the whole bacterium is the food.

Fully documentedOther10 days

Recipe

No fixed amounts recordedIndustrial continuous process; production amounts are not published. The process numbers are from a lab study in 200 mL bioreactors, and the composition is from the powder used in a safety study.
Xanthobacter sp. SoF1 (VTT-E-193585)Isolated from seashore sediment at Naantali, southern Finland[choi2026]
Hydrogen, carbon dioxide and oxygen gasesFed into the culture all the time[jamsa2023]
Mineral medium with ammonia as the nitrogen sourceModified DSMZ81 medium in the lab study[jamsa2023]
StarterXanthobacter sp. SoF1 (VTT-E-193585) from a culture collection; the lab study started inocula from glycerol stocks.

Total time across the recorded steps: 10 days

Start
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What changes: A small culture in mineral medium multiplies on hydrogen and carbon dioxide until it is dense

Step 1 of 4
Start a batch culture in mineral medium
Time
Not documented
Temperature
Not documented
Salt
None given
Acidity
Not documented

In the lab study the batch ran in modified DSMZ81 medium with 16.8 mM ammonium hydroxide as the nitrogen source; the continuous phase began once the culture reached an OD600 above 2. Output: dense starter culture.

Flavour
Not documented
Texture
Not documented
Colour
Not documented

Microbes at work in this step

the bacteria multiply on the gases until the culture is dense enough to run continuously

Method

Measured measured in a studySet fixed by a specification or tested recipeReported one source reports itTypical a general value, not sourced for this fermentUnconfirmed not yet checked against a source

At a glance

Solein is an industrial protein powder, not a traditional ferment. The bacterium Xanthobacter sp. SoF1 grows in a continuous gas fermentation, taking its energy from hydrogen and its carbon from carbon dioxide, and the cells are heat-inactivated and dried. The yellow powder is 68 to 73.1 % protein, depending on the conversion factor used, and the whole bacterium is the food. Made in 4 steps over 10 days. The longest step, run the culture continuously on hydrogen and carbon dioxide, takes 10 days (Jämsä T 2023) and runs at 30 °C (Jämsä T 2023). Xanthobacter sp. SoF1, a hydrogen-oxidising chemoautotroph does most of the fermenting.

Key numbers
Main step10 daysReported[jamsa2023]Run the culture continuously on hydrogen and carbon dioxide
Temperature30 °CReported[jamsa2023]Run the culture continuously on hydrogen and carbon dioxide
AciditypH 6.8Reported[jamsa2023]Run the culture continuously on hydrogen and carbon dioxide

What makes this one different

Unlike mycoprotein, which is fed sugar, this bacterium takes its carbon from carbon dioxide and its energy from hydrogen gas.

Related ferments

Variants

  • Other gas-fed protein microbesCupriavidus necator, another hydrogen-oxidising bacterium, has also been tested as a protein powder.

Safety

Safety studies found no genotoxicity in bacterial, cell and mouse tests, and a no-observed- adverse-effect level of 1500 mg/kg body weight a day, the highest dose given, in a 90-day rat study.

History and sources

Every number is labelled with how it is known. How this atlas is made

Wikipedia dates the launch of Solar Foods' pilot plant to 2019 [s1]. The company filed its EU novel food application on 29 October 2021 [solar-eu]. Singapore approved Solein as a novel food in September 2022 according to the company [solar-gras24], and in October 2022 according to Wikipedia [s1]; consumer products went on sale there in the summer of 2023 [s1]. Solar Foods announced self-affirmed GRAS status in the US on 2 September 2024 [solar-gras24] and submitted an FDA GRAS notification on 16 September 2025, expecting a no questions letter by the end of 2026 [solar-gras25].

  1. [choi2026] Choi B., Endres J.R., Clewell A., Hirka G., Béres E. 2026, In vivo mammalian micronucleus test in mice confirms lack of genotoxic potential of a protein-rich powder derived from Xanthobacter sp. SoF1, Genes and Environment 48:9paper
  2. [jamsa2023] Jämsä T., Tervasmäki P., Pitkänen J.-P., Salusjärvi L. 2023, Inactivation of poly(3- hydroxybutyrate) (PHB) biosynthesis in 'Knallgas' bacterium Xanthobacter sp. SoF1, AMB Express 13:75paper
  3. [choi2024] Choi B., Glávits R., Murbach T.S., Endres J.R., Hirka G., Szakonyiné I.P. 2024, 90-day oral toxicity study in rats of a protein-rich powder derived from Xanthobacter sp. SoF1, Journal of Applied Toxicology 44:1816–1830 (abstract)paper
  4. [klinzing2024] Klinzing K. et al. 2024, In vitro genotoxicological evaluation of protein-rich powder derived from Xanthobacter sp. SoF1, Journal of Applied Toxicology 44:1347–1360 (abstract)paper
  5. [caliskan2026] Caliskan C. et al. 2026, Techno-functional and nutritional evaluation of Solein single-cell protein and its application in non-dairy yoghurt alternatives, Food Research International 229:118467 (abstract)paper
  6. [s1] Wikipedia, Solar Foodswiki
  7. [solar-gras24] Solar Foods Oyj, press release 2 Sep 2024, Solar Foods obtains self-affirmed GRAS status for Solein in the United States (company source)web
  8. [solar-gras25] Solar Foods Oyj, press release 16 Sep 2025, Solar Foods has submitted a GRAS notification on Solein in the United States to obtain a no questions letter from the FDA (company source)web
  9. [solar-eu] Solar Foods Oyj, press release 2025, Solar Foods moves one step closer to introducing Solein to the European market (company source; gives the 29 Oct 2021 filing date)web