I found a link from my old favourite
focus magazine
...uses a special type of microbe that can grow by feeding on carbon dioxide, nitrogen and hydrogen. Using renewable energy, it splits the water molecules found in air, providing hydrogen.
The microbes are also fed a broth, including nitrogen, minerals, and other nutrients. Once the microbes multiply, they are separated from the liquid through centrifugation (separating molecules by spinning them really fast).
What is left is then dried into a fine powder that is roughly 60 to 70 per cent protein. This can then be used as a protein powder or turned into flakes, chunks or other shapes to mimic meats.
...
...hydrogen. The fermentation process relies heavily on it, and it has a habit of going boom.
It seems like a 'sledgehammer to crack a nut' problem. It needs electricity to generate the hydrogen, a 'special broth' to feed the microbes, a centrifuge to extract the microbes, then you get a powder that doesn't look very appetising.
For myself, I think I'd be harvesting white mulberry leaves and drying them, then grinding to a powder if I wanted a powder. The leaves give around 20% protein when they are dried, plus a load of other nutritional benefits. I eat plenty of them fresh (but cooked!) at the right time of year and it doesn't seem to need any inputs at all, except a bit of energy to cut it back down to size once a year when it tries to grow too big. But then that gives me a load of leaves to use as mulch on the veggie garden and some sticks for the rocket mass heater so it's all good. The leaves give around 20% protein when they are dried, plus a load of other nutritional benefits.
One of the links I found when searching for an article to link mentioned that the company had several patents out on the process too. Which always sets me on edge a bit. I'll take a selection of trees and plants and grow my own. My 'special broth' to make them grow is the contents of the pee bucket. Which seems about perfect to me...
Of course, if you were stuck on a space-ship for years it would be a different matter...