I have three bags of dried beans on my kitchen counter -- white, black, and red. Can I soak/pre-cook any them together -- maybe the red and black beans?
Yes, you can soak and or cook all of them together if you wish. I recently cooked up 3 kinds of dry beans I had from the farmer's market this summer with a smoked ham hock. We ate some and I froze the rest for soups later in the winter. I don't know of any reason not to cook them together unless you want to compare the flavor profiles.
I cook different varieties all together very frequently.
I'd soak and cook them separately so their colors don't bleed together. The black beans would turn the rest into a muddled brownish shade of ...em... p**py grayish yuck.
Thanks -- my major concern was different cooking times. My husband is vegetarian, so no smoked ham hock for us (sigh). I'll try it and see if the black/red beans bleed into the white or not.
Here's another thought, have you tried cooking them in an "Instant Pot" type of electric pressure cooker. I made a batch of ham and beans the other day, no soaking, just dumped everything and cooked on beans for 65 minutes. Tender, creamy, nummy! (1 lb. beans to 6 cups stock / water)