We cook meat to make it nicer to eat because it is more tender and flavorful than raw meat, and to make it safe to eat by killing harmful bacteria that may be on the meat. In order to be become better at cooking meat, it helps to know what meat consists of and what happens to it when we cook it. And so I am going to write a series of articles about this topic. In this first part I am going to explain the structure of meat, and show you how the cooking temperature affects juiciness. In the following parts I will cover tenderness, succulence, flavor, and appearance.
Meat used to be the muscle of an animal before it became meat. A muscle that the animal used to move, stand, breathe, etc. Muscles are protein fibers that are organized into bundles at different levels by collagen sheaths. Individual muscle fibers wrapped by the endomysium are called fascicles. This is what gives the meat its ‘grain’. A bunch of fascicles is bound together by the perimysium, and finally the whole muscle is sheathed in the epimysium (also known as the ‘silver skin’). Through tendons, the epimysium connects the muscle to the bone. If you compare a muscle to reinforced concrete, then think of the collagen sheaths as the steel and the muscle fibers as the cement.
Juiciness is the amount of meat juices that is released when you bite into a piece of meat. The more free moisture there is in the cooked meat, the more juicy it will be. Raw meat typically consists for 65%-70% of water. Most of that water is located between the protein filaments that make up the muscle fibers. When you cook meat, the temperature goes up. As the temperature reaches 40C/105F, the proteins begin to denature. Denaturing means that the proteins unravel and deform themselves, and the water is pushed out of the muscle fibers. Together with sugars, salts, protein fragments, nucleic acids, and other dissolved components of muscle cells, this water becomes flavorful meat juice. Near the surface of the meat the juices will escape, thus reducing the juiciness of the meat.
The process of denaturing and pushing out the water increases with the temperature. This is because at about 52C/126F the collagen will begin to unravel and contract, and the shrinking collagen will push out even more liquid. By 58-60C/135-140F, also the collagen sheaths surrounding larger bundles of muscle fibers will shrink and force the meat to constrict and shorten, forcing a flood of juices from the meat. By about 85C/185F the meat will be at its driest and toughest. It will still contain 55%-60% of water, but that water is mostly bound. The shrinking collagen will have pushed out most of the ‘free’ water that makes the meat juicy. This process will happen even if the meat is completely covered by water or other liquid while you cook it. So it does not help to keep meat covered as it is cooked, it will end up dry anyway.
All of this teaches us that meat will be at its juiciest when cooked to less than 52C/126F (i.e. hardly cooked at all), still quite juicy when cooked to a maximum of 57C/135F, and a lot less juicy when cooked to 60C/140F or more. A few degrees can thus make a big difference. To demonstrate this, I did an experiment with lamb rump steak (i.e. steak cut from leg of lamb). (Please note that although I used sous-vide cooking for this experiment, the information in this article is also applicable for other ways of cooking meat.)
I cooked 4 pieces of lamb rump steak cut from the same leg of lamb at 4 different temperatures (for one hour).
I weighed each piece before and after cooking as a good indication of the loss of juices.
The first was cooked at 55C/131F (‘medium rare’). Its weight went from 99 grams (raw) to 94 grams (cooked), or a weight loss of 5%. As you can see the meat looks very juicy and ‘loose’.
The second was cooked at 57C/135F. The weight loss was also 5% for this. The meat is slightly more cooked and this was my favorite.
The third was cooked to 60C/140F (‘medium’). The weight loss a whopping 18%! So even though it was cooked only 3C/5F higher than the previous, a lot more meat juices were lost. This is because of the impact of the second stage of collagen shrinkage that I explained above.
The final piece was cooked to 65C/149F (‘medium-well’), resulting in the same weight loss of 18%. The meat is a lot less pink than at the lower temperatures, because the myoglobin that makes the meat red will start to degrade at temperatures above 60C/140F.
I did not go any higher than 65C/149F, because I consider cooking meat well done to be a culinary crime!
It is clear from this experiment that the loss of juices does not increase gradually with the cooking temperature, but instead changes dramatically between 57C/135F and 60C/140F. This is why from the perspective of juiciness, you should try to cook meat to a maximum temperature of 57C/135F. But of course there are other factors that will determine how enjoyable the meat will be besides juiciness, and those will be covered in the next articles.