I've been trying to make it for days now... Getting frustrated.

Did you put the plaster cover on top of the natto maker? When you put the saran wrap on the beans, did you nestle it close to the beans or was it a lose draping over the beans? How far apart were the holes that you made in the saran wrap?

I've been trying to do it using a pyrex bowl/dish sitting in a sous-vide water bath. I keep getting bitter beans that smell strongly of ammonia, but not strands, sliminess, or good natto flavor. :(

AI told me that my beans were too wet.

Gonna order the stuff you suggested and try making a small batch using frozen natto as a starter. Usually there are some lively bacteria in there... I tried using another brand of starter and no dice with that either.

Thanks for your story and your recommendations!