Serious Eats - seriouseats.com

You just needed to let it cook a little bit longer. Meats that need to be slow-cooked like brisket, ribs, and pot roast tend to get tough before they get tender, You have to give it enough time to break down the muscle fiber. A little bit of acid, like tomato, or vinegar, or wine helps, too. Check with a fork at the end of the specified cooking time; if the meat does not slip off the fork, cook it longer. However, 10 hours at 200 for a brisket? Maybe in a crock pot. As for your rack of ribs at 200 degrees--I would cook it at minimum of 300 degrees. Sounds like they were undercooked. Just leave it in longer next time. Also you might want to get an oven thermometer to make sure that you oven is getting hot enough. Or cook on the stove in a big pot.