Using bean cooking liquid in soup
I soak dry beans in salted water (as per Cook's Illustrated), drain, rinse, and cook in fresh water, usually in the pressure cooker. I used to discard the cooking liquid but recently have begun including it in soup. Depending on the type of bean, the liquid can be rather unattractive, so I add tomato paste to improve the color. Add beef or chicken stock or base (depending on color of liquid), aromatic vegetables, and improvise a vegetable soup with your choice of seasonings. Today I included lentils, mixed vegetables, chopped-up leftover pot roast, and some of the beans (pinto) back in at the end. The bean liquid will thicken the soup, supplying more body even if you don't actually include legumes in the finished soup.
You do not need to soak the beans. You will notice after trying the unsoaked method that the skin will have a much better texture. Also you will not get the scum that forms on top. This is protein coagulating that has leeched out of the beans during the soaking process. Try cooking 2 pots simultaniously, 1 soaked and 1 unsoaked, this is what I did to convince me of the better method. It is a pretty debatable subject and will fire up as many arguments as a political discussion might. Here is an article I wrote on the subject after I tried the unsoaked method: