As the internal temp of your meat rises, its color is not the only thing that changes. A number of chemical and physical reactions take place, as the molecular structure of proteins and fats are altered by the heat. Different reactions kick in at different temperatures.
The temps shown here are approximate because other variables come into play such as the age of the animal, acidity, salt content, type of heat, humidity, etc. This info has been gathered from multiple sources including meat science research papers, textbooks, and Harold McGee's important book, On Food And Cooking. Click here for a complete guide to target cooking temperatures.
32°F. Water freezes. Meat stored frozen keeps much longer. Because water in meat is combined with proteins, the actual freezing temp of meat is often as low as 26°F. Water expands as it freezes and sharp-edged crystals form that can rupture cell walls creating "purge" when it is thawed, a spilling of liquid, mostly the pink protein fluid called myoglobin. Faster freezing makes smaller crystals resulting in less purge.
34-39°F. Ideal refrigerator temperature. Water is not frozen and microbial growth is minimized. You do have a good refrigerator thermometer don't you?
40-122°F. This is the temperature range where enzymes that tenderize meat are most active. Enzymes called calpains become ineffective at about 105°F. Other enzymes called cathepsins keep working up to about 122°F. Slow cooking can keep meats in this range longer so enzymes can be effective and tenderize. But slow cooking can be hazardous for ground meats and poultry. Read on:
41-135°F. As defined by USDA, this is the microbial "danger zone" in which bacteria grow most rapidly, sometimes doubling in number in as little as 20 minutes. According to USDA, cold foods must be stored below 41°F, and hot foods above 135°F.That's why we don't leave meats sitting around to come to room temp.
60°F. When chilling cooked meat, liquid gelatin from form a solid gel called aspic. Gelatin happens with the melting of connective tissues that wrap muscle fibers and connect them to bones, called collagen. Yep, it's the same stuff they inject under your skin to hide wrinkles.
95°F. Aspic starts melting.
95-122°F. Meat fats start to soften, melt, and drip away.
120°F. Myosin protein, a protein involved in muscle contraction within fibers, begins to lose its natural structure. It unwinds or unfolds, a process called denaturing. It starts to clump, gets milky, and starts to firm up the muscle fibers. Purple meats, called "rare", start turning red.
130°F. Pathogenic bacteria begin to die, slowly at first, but as the temp rises, they croak more rapidly. At this temp it takes more than two hours to pasteurize meat. At 165°F it takes just seconds.
130-135°F. "Medium rare" for most mammal meats, they are at optimum tenderness, flavor, and juiciness at this temperature. If you eat your meat well-done, you need to snap out of it.
130-140°F. Fats begin to melt and liquefy, a process called rendering. This is a slow process and can take hours if meat is held at this temp.
140°F. Collagens begin to contract and squeeze juice from within muscle fibers into the spaces between the fibers and out to the surface.Myoglobin, the pink protein liquid within muscle cells, denatures rapidly and red or pink juices begin to turn clear or tan and bead up on the surface. Meat gets noticeably tougher and drier.
150°F. Actin, another protein important to muscle contraction in live animals, begins to denature making meat tougher and drier still.
155°F. Known as "well done", meats are overcooked at this internal temperature. Much moisture has been squeezed out and fibers have become tough. Most (but not all) bacteria are killed in less than 30 seconds but spores can survive to much higher temps.
150-165°F. This is "the stall zone", when large cuts such as pork butt and beef brisket seem to get stuck for hours when cooked at low temperatures like 225°F. In this range, moisture evaporates and cools the meat like sweat on an athlete. Inexperienced cooks panic. Eventually temps start rising again. Whew!
160-165°F. Normal cooking temps kill microbes on the outside of meats rapidly so solid muscle meats are not likely dangerous since contamination is almost always on the surface. But ground meats and poultry often have bad guys beyond the surface so you must cook them beyond to the "instant kill zone" within which pathogenic bacteria die in seconds. That's why the recommended internal temp for ground meats is 160°F and for poultry is 165°F. When you reheat foods you should take them up to 165°F.
160-195°F. Tough collagens melt and form luscious tender gelatin. The process can take hours so low and slow cooking creates the most gelatin. Dehydrated fibers begin to fall apart and release from the bones. Meat becomes easy to shred. Even though the fibers have lost a lot of water, melted collagen and fat make the meat succulent.
190-205°F. Beef brisket, beef ribs, pork ribs, and pork shoulder are at their best because they are so full of collagen and fat.
212°F. Water boils at sea level. The boiling point declines about 2°F for every 1,000 feet above sea level.
225°F. The temperature I recommend for low and slow cooking of tough cuts. High enough so water evaporates from the surface to help form the desired crust called "bark", but low enough to get the most out of enzymes, collagen melting, and fat rendering.
230°F. Fructose, the predominant sugar in fruit and honey, begins to caramelize. Its chemical structure changes and it turns brown and develops richer, more complex flavors.
250-300°F. Butter starts to burn and smoke.
310°F. The Maillard reaction accelerates. This is the browning of the surface caused by chemical changes in proteins and sugars resulting in thousands of new molecules and the flavor we love in crusty brown meat. The Maillard reaction begins at lower temps, but really takes off at 310°F.
320°F. Sucrose (table sugar) begins to caramelize.
325°F. The temperature I recommend for crisping chicken and turkey skins because the Maillard reaction and caramelization move quickly at this temp.
350°F. Table sugar and brown sugar, which is just white sugar with molasses, in spice rubs and sauces begin to burn.
325°F. Pork fat begins to smoke.
400°F. Beef fat begins to smoke.
450-500°F. Nonstick surfaces begin to emit toxic gases.
570-750°F. Primary combustion temperature of wood. Hardwood smolders and releases large quantities of unburned gases including smoke.
600-700°F. The flash point or fire point, the temperature at which smoke from burning fat can burst into flame. Never use water to extinguish burning fat.
1,110°F. Secondary combustion of wood begins. Gases, cellulose, and lignin in wood burn rapidly if sufficient oxygen is present.