I have never heard of fermented black beans, so I did a google search on this. Here's what I found from a website called Ochef.com:
Fermented black beans are small, black soybeans that have been preserved in salt. Also known as Chinese black beans or salty or salted black beans, they have a very strong, salty flavor and are generally soaked for a half hour or so in fresh water before being added to a dish.
Fermented black beans are not the same thing as black bean sauce, although you can substitute the sauce for the beans in a pinch. The sauce is much more widely available in supermarkets, but you should look in the ethnic foods aisle anyway, and any Asian market will carry them. They are also available at EthnicGrocer.com, where they are listed as Salted Black Beans
Q. Is there a way of fermenting black beans at home? I have a Lemon Chicken recipe in an Asian cookbook that calls for this ingredient, but I was unable to find it in the grocery store.
A. It would be simpler to pack up everything you own and move to a new community, state or country where the grocery stores do sell fermented black beans. Yes, you can ferment the beans yourself. But first, look at what Susanna Foo says about it in her lovely book, Chinese Cuisine (Canada, UK): “Our Cantonese neighbor always made her own fermented black beans. She would mix black soybeans with salt, spices and gingerroot and let them sit out to ferment. She then sun-dried this concoction in her backyard for many days. During that time, the whole neighborhood acquired a pronounced smell, and my mother would complain that the odor was offensive.”
Ms Foo goes on to say how much she has come to appreciate fermented black beans as an ingredient, but pointedly does not give a recipe for making them yourself — and neither does any other Chinese or Asian cookbook that we consulted. Seriously, unless you live in the middle of nowhere, get on the phone with the manager of every nearby grocery store and shame them into getting fermented black beans on the shelves. And if you are in the middle of nowhere, order some online and pay the shipping, for heaven’s sake