No, it's not necessary. But it will reduce the cooking time! To soak black beans, cover the dry beans with roughly 3 inches of water in a large bowl. The beans will expand up to 3 times their size, so be sure to take this into account when choosing the size of the bowl. Let them soak for a minimum of 6 to 8 hours, or overnight in the fridge. If you can remember to soak them in the morning, they should be ready for you to cook them at dinnertime.