A few words on how the braising method works:
Meat consists of muscle tissue, fat and connective tissue. The two parts particularly important for understanding this method are muscle tissue and connective tissue. Muscle tissue is the part we recognize as meat and which, when cooked, looks like threads. Muscle tissue begins to release its juices at around 60°C. Connective tissue is the thin, transparent membranes we often ask our butcher to remove and which keeps the various sections of muscle tissue together. This tissue is rich in a protein called collagen which is very hard and begins to break down at around 80°C. As it breaks down it turns into gelatin.
Gelatin is desirable because, on the one hand, it absorbs some of the moisture lost from the muscle tissue during cooking making the meat more tender and, on the other, when diluted into the cooking juices it helps them thicken. One of the most important factors for successful braising therefore is to cook the meat at a temperature which ensures the breakdown of the collagen into gelatin but also keeps the muscle tissue at a temperature at which it will expel its juices for as little time as possible.