It seems as though there are several attitudes ranging from the straight forward simple to the lets throw the dice and hope it works method. As well as papers on large scale manufacture of soy sauce. I wanted to learn how to do it in an old school take your time and do it right mentality.
The first thing to do is source your ingredients. This consist of the following (with approximate cost);
-organic dried soy beans (local health food store) $6 for 5 pounds
-good quality whole wheat flour, I used King Arthur's Whole White Wheat (grocery store) &4
-Koji Kin mold spores in the form of a Homebrew Sake Kit (local homebrew supply) $8
-yeast, I am using an ale yeast SafAle US-05 (local homebrew supply) $3
-lactobacillus (local homebrew supply) $10
-sea salt (grocery store) $2
The next stage is to soak your beans in water for about 12 hours changing out the water at least once. When this is done change the water one last time and cook the living hell out of it until the soy beans break apart into a mealy texture between your fingers. This took about 3 hours for my over sized batch. Then let the beans cool in the cooking liquor then strain and begin to make a mash out of them achieving the smoothest consistency possible. Mine did not turn out very smooth since I started out with about 5 pounds of dried beans which I've since learned is way too much to mess with at home. At this point it's time to incorporate the flour I used 2 1/2 pounds of flour to 5 pounds of dried beans. This will dry out the mixture a fair bit and you can make patties out of it to let the fermentation begin. Once the patties are made (mine ended up being the size of a half sheet pan) it's time to inoculate with our safe mold spores (the same ones used to make sake) I took a few grams of the mold spores and mixed with white flour and then sifted over every inch of my soy paste then moved them out of the way and covered with a damp paper towel to let the transformation begin. It only took about a day to see the signs of the Koji Kin working on the soy mix with the fine white hairs as instructed in the sake making kit that would be present. This is a very positive sign that we're on the right path. I think in the next day or two I will dry this mix out the rest of the way and begin the second fermentation with the lactobacillus and yeast. Sine my yeast is not a salt tolerant variety I will minimize the salt for the first few days to let the yeast do it;s thing on some of the converted sugars from the Koji Kin.
By introducing the lactobacillus this will become a very long process I believe to turn into a finished product. It's my goal to split this into a few small batches to try different aging methods like different woods and just on it's own.