Before washing black beans, spread them out on a light colored plate or cooking surface to check for, and remove, small stones, debris or damaged beans. After this process, place the beans in a strainer, rinsing them thoroughly under cool running water.
To shorten their cooking time and make them easier to digest, black beans should be presoaked (presoaking has been found to reduce raffinose- and stachyose-type oligosaccharides, sugars associated with causing flatulence.) There are two basic methods for presoaking. For each you should start by placing the beans in a saucepan and adding two to three cups of water per cup of beans. The first method is to boil the beans for two minutes, take the pan off the heat, cover and allow to stand for two hours. The alternative method is to simply soak the beans in water for eight hours or overnight, placing the pan in the refrigerator so that the beans will not ferment. Before cooking the beans, regardless of method, drain the soaking liquid and rinse the beans with clean water. We realize that there has been some debate in the public press over discarding of the bean soaking water. Some websites and commentators have argued that this soaking water contains too many valuable nutrients to discard. We believe that a recent study has helped to put this controversy to rest by comparing a wide range of factors involved with the content of the soaking water. Research analysis has shown that getting rid of the soaking water also means getting rid of some of the phytates and tannins that can lower nutrient availability, as well as flatulence-related substances like raffinose (up to 33% removed along with the soaking water) and stachyose (up to 20% removed). Discarding the water will result in an unwanted loss of total phenols, but the extent of that loss will be relatively small (about 15%). While some of the total carbohydrate content in the black beans will be lost along with the discarded soaking water, the amount of digestion-enhancing resistant starch will remain unchanged.