<<Disclaimer: Verify this information before applying it to your situation.>>

I recently posted a list of GF soy sauces that I gleaned from this list's
archives. I received the following comment on Eden's imported wheat-free
tamari:

Just a comment on this listing.  The referenced soy sauce is made with "koji-
innoculated" soybeans.  Koji is malted barley.  The ingredients appear to be
gluten free, but if you read on the side of the bottle on how it is made, I
don't see how it can be gluten free.  I figured this out after reacting to
eating it.

Now I didn't remember anything about koji. So I searched the archives for
the word. I found 17 matches. One specifically referred to the Eden tamari:

   Eden Foods 1-800-838-2326.  I learned that all of Eden's products with
   koji as an ingredient are rice-based according to Eden rep Cindy Eicholtz.
   She wants all you food chemists to know she's talking about aspergillus
   oryzae, a culture grown on rice.

But sometimes it seems it can be from barley. Some other archive findings:

   Koji is a fungus.  I believe the genus is aspergillus.

   Koji is defined in macrobiotic cookbook glossaries as a grain/seed
   inoculated by a bacteria. There doesn't seem to be any guarantee that the
   grain used is always rice. Besides sake, koji is used in making other
   fermented foods: tamari soy sauce, miso (a paste), amasake (a sweet drink)

   KOJI--A grain inoculated with bacteria and used in making fermented foods
   such as miso, tamari soy sauce, amasake, natto, and sake.
   Please notice that not all koji is necessarily made from rice, but it seems
   that Maria-Louisa's is a rice product.

   Koji--can contain barley because it comes from Miso

Westbrae Natural ingredients.  They are as follows:  whole soybeans 57%,
water 28%, sea salt 12%, marin (cultured rice) 2%, koji (cultured barley) 1%.

As for Amazake, it may be gluten-free but we haven't been able to
determine that conclusively. We use an ingredient called koji which is a
cultured rice that comes from Japan. Our source for it, Miyako Oriental
Foods in Brea, California, has not been able to tell us whether there are
any other grains used in the processing besides rice.