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Thank you to all the people who commented. The first post (Chris
Hawkins) seemed to know the most about the process, the others had
various guesses about it. According to Chris, they should be safe. I
will try them again, but very carefully and I'll definitely wash them
first as he suggests. I wondered however, if it was possible that they
used traditionally brewed soy sauce instead of salt, hence exposure to
wheat.

I have lived in Hong Kong for many years and frequently do Chinese
cooking and use alot of black beans in my cooking.  They are simply soy
beans and salt allowed to ferment by themselves.....they are pretty old
and matured.  But nothing else is added to them.  Make sure though that
you wash them thoroughly before use, and then the best way to prepare
them is to take a teaspoon of the beans, a teaspoon of oil and a
teaspoon of sugar and put in a heat proof container sitting in a pot of
boiling water for 5 mins.  They just cook enough to soften and then can
be mashed.......I stirfry them into the hot oil before I add stuff, or
add later as part of a sauce.  And they are delicious.  I don't think I
have ever had problems with eating them.

I think quite a lot of fermented products use yeast that has been grown
on wheat based nutrient, although I' m sure someone else will know more.
Regards,Jen Smythe

Could it be fermented in some kind of vinegar? Fermented to me, brings
vinegar to mind.

Some people do seem to have reactions to soy which are not
coeliac reactions.  If you are convinced that the reaction
you get IS coeliac, then I would suspect contamination.
This can be a real problem, as the food industry (which I
have worked in over here many years ago) is only really
interested in whether something is within the bracket of
fit for human consumption or not.  Thus it is quite easy
for wheat flour to creep in as a non-stick substance in a
process, by accidental transfer from a non-GF process going
on in the next vat and so on.  If you now purchase your
material from a shop which sells it from a large container
then you have another step where contamination can occur.

I am not able to eat beans of any kind without intestinal upheaval, even
gf.

I know nothing about fermenting black beans but have made sauerkraut
(cabbage and salt).  To make sauerkraut we chopped the cabbage, tossed
it with salt and packed it into the canning jars tightly.  Similar
procedure used if putting it into a crock or barrel.  It was then set
aside to ferment.  The Chinese beans may be have done the same way.
Sauerkraut does not agree me.  I'm the celiac in this family.