Here is some good info about Braising meat from cooks illustrated.
Published September 1, 2008. From Cook's Illustrated.
What is braising and how does it turn tough cuts of meat tender?
Braising calls for slowly simmering food in a small amount of liquid in a tightly covered pot. (The temperature of the simmering liquid is 180 to 190 degrees.) Braising is most often used for tough cuts of meat that need to cook gently until tender. Braised items are usually browned in hot oil before aromatics and flavorful liquids such as wine or stock are added.
While a variety of cooks have put forward theories about why and how braising works, we wanted hard facts explaining the mystery of braising and set up a handful of tests.
Before kitchen testing began, we researched the meat itself to better understand how it cooks. Meat (muscle) is made up of two major components: muscle fibers, the long thin strands visible as the “grain” of meat, and connective tissue, the membranous, translucent film that covers the bundles of muscle fiber and gives them structure and support. Muscle fiber is tender because of its high water content (up to 78 percent). Once meat is heated beyond about 120 degrees, the long strands of muscle fiber contract and coil, expelling moisture in much the same way that it’s wrung out of a towel. In contrast, connective tissue is tough because it is composed primarily of collagen, a sturdy protein that is in everything from the cow’s muscle tendons to its hooves. When collagen is cooked at temperatures exceeding 140 degrees, it starts to break down to gelatin, the protein responsible for the tender, rich meat and thick sauces of braised dishes.
In essence, then, meat both dries out as it cooks (meat fibers lose moisture) and becomes softer (the collagen melts). That is why (depending on the cut) meat is best either when cooked rare or pot-roasted—cooked to the point at which the collagen dissolves completely. Anything in between is dry and tough, the worst of both worlds.
Time and Temperature
This brings us to why braising is an effective cooking technique for tough cuts of meat. To determine the relative advantages of roasting, braising, and boiling, we constructed a simple test. One roast was cooked in a 250-degree oven, one was braised, and one was simmered in enough liquid to cover it. The results were startling. The dry-cooked roast never reached an internal temperature of more than 175 degrees, even after four hours, and the meat was tough and dry. To our great surprise, both the braised and boiled roasts cooked in about the same amount of time, and the results were almost identical. Cutting the roasts in half revealed little difference—both exhibited nearly full melting of the thick bands of connective tissue. As far as the taste and texture of the meat, tasters were hard pressed to find any substantial differences between the two. Both roasts yielded meat that was exceedingly tender, moist, and infused with rich gelatin.
Dry heat (roasting) is ineffective with tough meat because the meat never gets hot enough to fully melt the collagen. It does not appear that steam heat (braising) enjoys any special ability to soften meat over boiling. Braising has one advantage over simmering or boiling, however—half a pot of liquid reduces to a sauce much faster than a full pot.