What is the lowest and slowest way I can bake pork ribs?

To achieve "done" pork ribs should reach an internal temp of 160°F (71ºC). The longer it takes to get there be more tender they will be. I would not recommend going any lower than 200°F (93ºC) for your cooking temp, even if that means turning the heat up a little at the end to reach your internal temp of 160°F. Put a good rub on, wrap the racks of ribs (individually) in aluminum foil, with some beer or cola in there (or other braising liquid) and let them go. For a video of how to do this watch this episode of "Good Eats" All of that said, I have never tried to let the ribs go 7 hours unattended, so I would try it when you have the time to hang around and monitor the internal temp, again looking for 160°F internal temp and that will give you a means to determine what is "done".

I use this guy's technique for grilling ribs, which calls for 5-6 hours at 225°F (105°C) on a grill or smoker (3-4 hours for baby backs). I've done them many times this way and they're absolutely delicious. I don't see any problem at all upping that to 7 hours and lowering the temp to 200°F (95°C). I wouldn't wrap them in foil or add liquid, but I probably would tent them with foil.

And assuming you have a modern gas or electric stove, there should be no problem leaving it on while you're away. People do that the world over every day.

Well, by far the "lowest and slowest" technique out there is sous vide. (Basically, cooking in a precisely controlled temperature water bath.) The typical way to do this involves three steps:

1. Marinate, rub, and/or smoke your meat (optional). Smoking is often preferred since the meat won't go on a grill for a long time, and it helps get that rich flavor you'll want.
2. Vacuum seal the meat and drop it in your circulating water bath for a long time. Typical temperatures for the water are 135-160 F, with times ranging from 8 to 48 hours. [See: low and slooooow]
3. Finish the ribs over very high heat very briefly—just enough to sear the outside.

The advantages of the technique include ultra-tender, medium-cooked meat that's relatively easy to get "right". Highly recommended.

There are many recipes out there (Google "sous vide ribs"). This one, for example, seems good without too much fuss. Of course, you should use your own recipe for the rub and sauce if you've got a favorite!

It really depends on the amount of ribs you are cooking, the more meat, the more time - 1hour to 1 hour 20 min per pound works well, when cooking at 200 degrees. I have many times put 4-6 racks in the oven and baked them through the night(deep hotel pan, tightly wrapped foil), no salt, just plenty of seasonings (without salt) they held the texture nicely but were moist and the meat could fall off the bone with little effort. Then salt at the last minute before you serve while on the grill. (salt draws moisture out) My longest cook time thus far has been 13+ hours at 200 degrees. Usually 5-6 hours works for only 2-3 small racks you just want them to be nice and tender but not falling apart so much that they cannot hold their shape while on the grill.

If you drop the cooking temperature low enough, you should be able to let the ribs cook for 7-8 hours. At 225f or 250f, I would be worried about coming home to a mushy mess, but at 200f it should be about right. You definitely do not want to foil your ribs. That will speed the cooking process, which you do not want. I would be pretty hesitant to cook a roast or a whole animal at such a low temperature, as the volume of meat that is away from the surface could keep the interior at unsafe temperatures for too long, but with ribs there should be no safety issue.

I love slow cooked baby-back-ribs. Yesterday, about eight hours before my company arrived, I preheated my oven to 350 degrees. I then took the baby-back-ribs out of the package and removed the membrane. I then put on a store bought dry rub and sealed the ribs in aluminum foil. I also did the same thing with a package of fajitas, except I used fajita seasoning.

I put the meat on a rack in the hot oven and turned down the oven to 170 degrees. I left it alone for seven-and-a-half hours. I then took the meat out of the oven and poured off the liquid in the foil. I took the meat out of the foil and put BBQ sauce on the ribs and then put the meat on a rack in the oven and set the oven to broil. When I got the degree of char I wanted, I took the meat out of the oven and let it rest for ten minutes.

Both cuts of meat were very tender. The ribs did not fall off the bone, but were firmly attached. You had pick up the bone and eat the meat off the bone. If you want the meat to fall off the bone, soak the meat in a marinade overnight.