How Slow Cooking Works
In a nutshell, slow cooked meals are generally easier to make and very cost effective using cheap cuts of meat that improve in texture and flavor when cooked for long periods of time over a very low heat source. These tough cuts of meat are made up of large amounts of collagen and therefore require longer cooking times to break down into a rich gelatin.
When you cook or smoke beef, pork, poultry or fish, collagen contained within begins to melt at about 160°F and turns to a rich liquid, gelatin. This gives meat a lot of flavor and a wonderful silky texture. When cooking it is important to liquify the collagen.
Denaturation of the collagen molecule is a kinetic process, and hence a function of both temperature and duration of heating. Cooking at low temperatures require long periods of time to liquify collagen.
COOKING MEAT TEMPERATURES
105°F - 122F° Calpains begin to denature and lose activity until the temperature reaches around 105F, and cathepsains at 122°F. Since enzyme activity increases up to those temperatures, slow cooking can provide a significant aging effect during cooking. Meat should however be quickly seared or blanched first to kill surface microbes.
120°F Meat develops a white opacity as heat sensitive myosin denatures. Coagulation produces large enough clumps to scatter light. Red meat turns pink.
120°F - Rare Meat: This is the early stage of juiciness in meats as the the protein myosin, begins to coagulate. This lends each cell some solidity and the meat some firmness. As the myosin molecules bond to each other they begin to squeeze out water molecules that separated them. Water then collects around the solidifyed protein core and is squeezed out of the cell by connective tissue. At this temperature meat is considered rare and when sliced juices will break through weak spots in the connective tissue.
140°F Red myoglobin begins to denature into tan colored hemichrome. Meat turns from pink to brown-grey color. It is a this temperature that eat suddely releases a lot of its juices, shrinks noticebly, and becomes chewy as a result of collagen denaturing which squeezes out liquids.
160°F - Medium to Well Done Meats This is the state where Collagen shrinks as the meat tmeperature rises to 140°F. More of the protein coagulates and cells become more seggregated into a solid core and surrounding liquid as the meat gets progressively firmer and moister. At 140°F - 150°F the meat suddenly releases lots of juices, shrinks noticeably and becomes chewier as a result of collagen shrinkage. Meat served at this temperature is considered medium and begins to change from juicy to dry. Once the meat reaches 160°F, the connective tissue collagen begins to dissolve to gelatin. This melting of the collagen starts to accelerate at 160°F and continues rapidly up to 180°F.
Well Done Slow Cooked Meats: Fall-off-the-bone tenderness collagen turns to gelatin at 160°F. The meat begins to dry out, but at 160°F the connective tissues containing collagen begins to dissolve into gelatin. With time, the muscle fibers that had been held tightly together begin to easily spread apart. Although the fibers are still very stiff and dry, the meat appears more tender since the gelatins provide succulence.
NOTE: At 140°F changes are caused by the denaturing of collagen in the cells. Meat served at this temperature is considered to be med-rare and is beginning to change from juicy to dry. At 160°F connective tissue collagen begins to dissolve to gelatin. This however is a very lengthy process. The fibers are still stiff and dry but meat seems more tender. Source: Harold McGee -- On Food and CookingAnatomy Of Muscle Fiber
Muscle is completely enclosed by a thick sheath of connective tissue (the epimysium) and is divided into bundles of fibres by a connective tissue network (perimysium). Individual muscle fibres are bounded by a plasma membrene surrounded by connective tissue (endomysium) which consists of a basement membrane surrounded by a reticular later in which a meshwork of fine collage fibrils is embedded in a matrix. Tendons are elastic collagenous tissues. Source: Wikipedia
Scattered among the muscle fibers are fat cells which store energy for the muscles. Fat is crucial to meat texture. Waxy when it is cold, fat does not evaporate when you are cooking as does water. It melts and lubricates the fibers as they are getting tougher under the heat. Fat is also the source of much of the flavor in meat. As the animal ages the flavor compounds build up and get stronger. After the animal is slaughtered, the fat can turn rancid if stored improperly or too long.
The Challenge In Cooking Meat
Because we like our meat tender and juicy at the same time, we want our meat to be cooked tender to the point that tough collagen is converted to gelatin, but with a minimum loss of moisture. The reality of this is that these methods contradict each other and hence the challenge or dilemma to cooking meats. To minimize moisture loss requires temperatures of less than 130°F. However, converting collagen into gelatin requires temperatures above 160°F and for extended periods of time. As moisture evaporates, the meat begins to shrink. A slab of meat can lose 20% or more of its weight while cooking due to shrinkage. Even meat cooked in liquid will dry out although not as quickly. So we are faced with a dilemma. To liquefy the collagen we need to cook the meat to at least 180°F and hold it there for long periods, but by then it is well past well-done and the muscle fibers can be dryed out. As a result, we need to add moisture.
How To Slow The Loss Of Moisture
Brining: Brining adds a significant amount of moisture to any piece of meat, pork or poultry. Brining helps retain moisture during cooking while contributing noticeable flavor enhancements.
Steaming: Another method of adding moisture is to cook the meat in very high humidity by wrapping it in foil with a little water or juice. This method keeps moisture from escaping and some vapors penetrate the meat.