MEAT COOKING SCIENCE
Cooking meat perfectly is something of an art, even though it's not that hard to learn as some people think. The point when cooking meat is to make it tender and moist, in other words, to avoid transforming a nice cut into tough and dry meat. Meat becomes tender as its connective tissue is melted in the heat, but at the same time, the heat contributes to evaporation of water (which makes the meat dry) and toughens the muscle fibers. So, if we focus too much on having it tender, we might lose the juices of the meat. We need to find a balance between the two desired states of the meat texture. The somehow tricky part is that all cuts of meat are different and they all require a special approach. Tender meat, since it is already tender and doesn't have much connective tissue in it, is best cooked by quickly heating it to the point where the moisture is flowing at its best. Tough cuts of meat though need more time to become tender, because their connective tissue needs to be melted thoroughly in the heat. For tender meat then we can use quick roasting or frying, while the tough meat is best braised and in stews. This is a general rule.
You will probably discover that the very same cuts of meat from the very same shop may not behave similarly each time you cook them. No big surprise, the meat toughness depends highly on the animal, its age, genetics, exercise, and a lot of other factors that can influence the texture of the meat. In this case, it is necessary to learn how to handle each cut of meat individually, instead of learning "how many minutes" formulas. We need to be able to judge if the meat is cooked or not by other means.
The most tricky meat to cook properly is the tender meat. It is easy to dry it out by applying just a minute extra time on the frying pan. The difference between medium rare and "well-done" (read: dry) is a matter of a narrow span of temperature in which the meat is cooked. The hard part for the beginners is to judge the inside of the meat - the surface may look good, but what happens on the inside? How can we know if the meat really is cooked but not overcooked? At which point shall we stop the cooking process? One way to tackle the problem is to decrease the flow of heat into the meat. This is often done by wrapping the meat in other ingredients, like bacon or pastry, which would act as heat-insulators, slowing down the heat penetration. This allows us to be more flexible on time during which we cook the meat. Then, one minute more or less shouldn't matter as much as it would if we would directly fry the meat. Another way to slow down the penetration of the heat is to quickly brown the surface of the meat at high temperature and then cook it slowly at lower temperature. One can also terminate the heating before the meat is completely done and let it cook by its own afterheat for a while. It must be remembered though that thinner cuts of meat lose their heat more quickly than the bigger pieces, so they may not be that suitable for afterheating cooking.
A lot to think about? Yes, but it becomes easy after a while of practice. Remember: you need to know when to STOP cooking. There is no clear formula for how many minutes in a certain temperature a meat needs to be cooked. Every cut must be treated on its own. The best way to do so is probably to use a thermometer that you can stick into the meat, and monitor its inner heat. Depending on how you want the meat to be done, you terminate the cooking as the temperature approaches the desired level (rare 50C/120F, medium 60C/140F, well done 70C/160F). If you have a smaller cut of meat, the thermometer might not be so useful - then cut the meat and see how it looks inside. A more flexible (professional) way is to touch the meat with your finger and determine its doneness. Rare meat is very soft although a little tougher than raw meat, and some juices are sweating on the surface (it's not blood!). Medium is even firmer to the touch, and more juices appear on the surface, while the inner part of the meat becomes pink. Well-done meat is pretty stiff, the color is brown/gray, and it's dry. Avoid well-done if you want the best flavor, unless you are making a stew out of a tough meat (that frankly needs to be well done, but it's kept "artificially" moist by the liquid of the stew. As for the pink meat, remember to buy it from hygienic vendors to prevent food poisoning. Although bacteria mostly reside on the surface of the meat, which is usually browned in high temperature (killing the bacteria), it's best to be safe. In any case, it is not very probable to get poisoned by pink beefs. Bacteria are mostly a problem in the ground meat, which needs to be cooked thoroughly. If you can, grind the meat at home after browning its surface or blanching it quickly in boiling water. Bacteria will get killed and you can also prepare and eat your ground meat dishes pink!