Making soy-free miso paste at home is embarrassingly easy, especially now that we can now use the internet to order pre-cultured koji rice. As this is a sweet miso, it only takes a month to ferment at room temperature (opposed to red miso that requires minimum one year). This live culture food is wonderful in dips, stir fry sauce, glazes, and yes, even miso soup.
You'll need a gallon vat to ferment the miso in. This can be made from anything non-reactive (I use the pottery liner from a busted slow cooker). Pottery, glass, or even plastic makes a great vat, however, metal can react with the salt and fermentation in the miso to impart bad flavours or damage your container.
Koji is actually a mold that has been grown on the rice (koji rice) that converts the starch in the rice into sugars which can then be fermented. Koji is only just beginning to be recognized for some of it's amazing health benefits - something that traditional Japanese culture already knew for centuries. You can culture your own koji rice at home, though it takes a few days and careful temperature control. Better yet, buy some already cultured koji rice for this recipe. —trampledbygeese