Filet mignon loses about 13 percent of its weight during cooking. Meat comprises roughly 75 percent water, 20 percent protein and 5 percent fat, although the percentages vary depending on the particular cut. Filet mignon, for example, has next to no visible connective tissue or fat, so you can expect almost all of its shrinkage to come from water loss. That doesn't mean you have to settle for a dry steak, though.
Meat and the Cooking Process
A lot more happens to a steak during cooking than you see in the pan. Before the filet comes in contact with heat, its protein fibers resemble tightly coiled tubes filled with water and held together by collagen bonds. Heat breaks the collagen bonds holding the fibers together while forcing the water they contain out, which causes them to shrink in length and width. The protein fibers then reform, or coagulate. The fibers then resemble unraveled, spindly tubes markedly smaller than before. During unraveling and coagulation, a process referred to as denaturing, meat loses about 13 percent of its weight.
What the Filet Mignon Loses
Filets don't have much fat or connective tissue, that's why they stay tender and juicy when you cook them to medium-rare or medium, but dry out quickly and toughen when you cook them further. Because the filet has little to no fat to melt and render out, almost all the 13 percent weight loss is moisture.
Minimizing Moisture Loss
You have to cook filet mignon quickly with high heat and never cook it above 130 degrees Fahrenheit, or medium-rare, to retain as much moisture as possible. To cook a filet to a textbook medium-rare, start by letting it reach room temperature on a plate. Heat about 1 tablespoon of oil in a saute pan over medium-high heat for several minutes. Season the filet to taste all over and place it in the hot oil. Sear the steak for 1 1/2 to 2 minutes and turn it over with tongs. Cook the filet another 1 1/2 to 2 minutes, then sear the sides of it just long enough to add color while holding it with tongs. Take the filet out of the pan and let it rest on a plate for 5 to 7 minutes.
Resting Filet Mignon
Resting plays a part almost as important as proper cooking does in minimizing filet shrinkage. During cooking, the moisture in the protein fibers moves outward where it evaporates, but not all of it. Some moisture stays in the fibers -- unless you burn it to a crisp -- but it's concentrated closer to the surface than the center. When you remove the filet from heat, the moisture that moved outward reverses direction and moves towards the center. The redistribution of moisture occurs when you let the filet sit undisturbed after cooking, or during the rest period. If you don't rest the filet and slice it right after cooking, it loses an extra 9 percent of its weight, bringing the total amount lost during cooking to 22 percent. After cooking the filet, let it rest for 5 to 10 minutes before you cut into it.
Medium-Rare Steak and Safety
The U.S. Department of Agriculture advises cooking beef to at least 145 F, or medium-well, to reduce the changes of foodborne illness. The chances of healthy people getting sick from a fresh medium-rare filet mignon are rare, because harmful bacteria and pathogens are on the surface of the meat, not the interior.
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