Natto needs an oxygen to ferment.

I’ve switched from glass dish to bamboo steamer that you find in chinese dim sum cooking mainly because I found that if you stack up soy beans too deep, the result is not favorable.  Since bamboo steamer has top and bottom open to the air, I can put natto as high as 5 cm thick and they come out fine.  That said, bamboo steamer is high maintenance tool as bamboo can absorb natto-kin and if you let the natto-kin stay in the steamer, they turn into molicious one which can kill good one very quickly.

I usually buy soybeans from local coop.

Hi,

I usually buy soybeans from local coop.

If you are looking for extra small beans designed for Natto, you may need to import from Japan.

I buy soybeans from the below producer.

http://www.grainplacefoods.com/

You may want to call them to find out their local distributor in your area.

I hope this helps.

Thanks

Dice-K