Black bean sauce is a sauce made from fermented black beans.A popular technique is to mash the beans and combine them with garlic and/or ginger. The mashed bean/garlic/ginger mixture may be rubbed over meat or seafood prior to cooking, added to the heated oil at the beginning of stir-frying, or combined with other liquid ingredients and poured over steamed dishes. They are available in the market as Prepared Chinese black bean sauce. This Chinese black bean sauce does not require further cooking, and just needs to be heated through. In stir-fries, combine the black bean sauce with the other sauce ingredients, and add to the wok in the final stages of cooking. Follow a similar procedure for steamed dishes, combining the prepared black bean sauce with the other sauce ingredients, adding the sauce to the food and steaming according to the recipe directions. Don't try substituting black bean sauce for mashed black beans as a rub over meat or seafood before cooking - the results won't be very good. Think of it as a sauce and proceed accordingly.