Recooking beef in a liquid or sauce may make it tender, depending on why it's tough to begin with. A tough cut of beef, such as chuck roast, for example, will be made tender by cooking it again, especially if it wasn't cooked long enough the first time. But not every cut of meat can be tenderized through cooking. Stick with a liquid, rather than a sauce, when recooking beef, because sauces are more likely to burn.
Some cuts of beef were made for long cooking in sauces or liquids. These cuts, such as brisket, chuck roast and bottom round, contain a lot of connective tissue and intersecting muscles. They must be cooked to temperatures of around 185 degrees Fahrenheit. At this temperature, the connective tissue melts into gelatin, and the tough meat fibers break down. If you didn't cook one of these cuts long enough, you can certainly recook it in liquid to tenderize it. Just keep the temperature low and plan on a few hours of cooking time.
How to Do It
To recook a tough cut of beef to tenderize it, place the meat in a slow cooker or a heavy lidded pot. Add 2 to 3 cups of liquid -- enough to cover it halfway, but not submerge it. Place the lid on the slow cooker or pot and gently simmer the meat until it's fork tender. Plan on six to eight hours in a slow cooker or two to four hours in an oven set at 300 degrees Fahrenheit. Do not allow the liquid to boil, which will toughen the meat, and add more liquid, if necessary. If the meat wasn't previously browned, brown it first in a bit of oil on the stovetop. Browning takes about five minutes and adds flavor, color and moisture to the meat. Refrigerate the meat until you're ready to use it, and cook it slowly over low heat. Select a liquid that complements any seasonings you've already used on the meat.
In the Sauce
In most cases, it's best to braise tough cuts of beef in a liquid, such as beef broth, red wine or apple juice, rather than a sauce. Sauces or gravies may contain flour or cornstarch. Flour may burn with long, slow cooking, while cornstarch breaks down. Once the meat is tenderized, you can thicken the liquid to make a sauce. Simmer it to reduce it or thicken it with cornstarch, flour or potato starch.
Exceptions to the Rule
Tender cuts of meat, including tenderloin and prime rib, taste best when they're cooked to medium-rare. If they're tough, they may have been overcooked the first time, and cooking them again probably won't improve matters. In this case, just heat the meat gently with a gravy or sauce and slice it thinly across the grain, or in the opposite direction of the meat fibers running through the meat. You can also use this strategy for steaks or London broil. Thinly sliced, the meat can be dressed up with a sauce or used in stir-fries, fajitas or sandwiches.