I made another batch of natto over the holidays, I think the best one yet. I used a starter culture of hot water, 1tbsp of brown sugar, 1tbsp of white sugar, 2 tbsps of malt extract, and 1 tbsp of malto-dextrin. When it had cooled down a bit, but was still warm I added in a package of frozen commercial natto and stirred.
I made four batches of soybeans in a pressure cooker (500g dry weight each). The starter went into the first batch. Each subsequent batch was mixed into the previous ones. Finally it was all divided into 4 pyrex trays and went into a large picnic cooler with an electric heating pad.
warby
49-M