Bitter? Hmmm, I don't know what you mean, either. We cook lots of pintos at my house, and black beans, too. I do them in the pressure cooker; they're soft and tender, no split skins. If you have a pressure cooker, this is what to do:

Perfect Pinto Beans
Sort and wash the dry beans. Be sure you wash them clean in cold water, because you will use the finished bean liquor for many of your dishes. Do not discard it. Cover the beans with twice as much water as beans, bring to a boil, boil for one minute, let sit an hour without heat, with the pc lid on. Many of the beans will float. That's OK.

After an hour, check to be sure you still have double the water over the beans, add more if necessary, bring them up to pressure and cook 6 or 7 minutes. Let pressure fall of its own accord.

That's all there is to it. Perfect Pintos every time. They'll keep in the fridge for a week. From one pot of beans, you can use the beans and their liquor as base for bean soups, rinse and drain some for salads, mash some for tostadas or tacos, eat a bowl of whole pintos with cheddar cheese and onions.....

We love Bean Tostadas:/

In a small frying pan, heat a tsp or so of olive oil, add a minced garlic clove, a dash of salt, a spoonful or two of cooked beans with their liquor. Mash beans in the pan while they are heating, add more liquor if you need it, or continue cooking til beans are the consistency you want. Spread this on a crisp corn tortilla, and top however you like, or make burritos in a flour tortilla. It's bliss!

Sherry