As a tough cut of beef, rump roast is best grilled low and slow over indirect heat. Cut from the bottom round, rump roast can be boneless or bone-in, which is then known as a standing rump roast. Cooking it slowly allows the beef's fatty connective tissues to slowly dissolve into the meat, making it extremely tender. Alternatively, cooking it on the grill gives it a distinctive charred flavor. Brine the beef ahead of times to infuse it with extra flavor and moisture. Serve the grilled roast beef with your favorite grilled vegetables.
Create a basic brine for your rump roast by combining 4 tablespoons of salt for every 1 quarter of water in a large container, adding enough water and salt to fully submerge the roast. You can add additional herbs, spices and flavorings to the brine as well, to your taste. Alternatively, you can replace some or all of the water with beer, wine or sodium-free beef stock.
Submerge the rump roast in the brine and store it in the refrigerator for 8 to 24 hours. Remove the roast from the refrigerator and the brine about an hour before you start grilling to allow it to come to room temperature. Pat excess moisture off the roast with paper towels.
Prepare a charcoal grill for indirect heat by piling your charcoal on one side of the grill and placing a large drip pan on the other side. Light the coals and close the lid. If you are using a gas grill, turn all the burners on high for 15 minutes and close the lid to preheat, then turn off one side of the grill and turn the other burners down to a medium-low heat.
Place the roast directly over the flames on you grill to sear, using barbecue tongs to turn it over and sear all sides until well browned.
Move the roast to the other side of your grill, away from the flames and cover. Allow the roast to cook for roughly 20 to 30 minutes per pound, turning it every 30 minutes to ensure even cooking. You can also brush the roast with any type of flavoring sauce, such as a barbecue sauce, a honey mustard sauce or a combination of sauces.
Remove the roast from the grill when it has reached an internal temperature of at least 145 F, as recommended by FoodSafety.gov for safe consumption, which will bring your roast to about a medium temperature. Take it off 10 to 15 degrees sooner for a rarer level of doneness. Allow it to rest for about 15 to 20 minutes before slicing and serving.