Rotisserie grilling is one of the best preparation options for bottom round roasts because the meat cooks slowly over a long period of time without direct, high temperatures. Bottom round roast comes from near the hind legs and contains connective tissue and lean meat that can be tough and chewy when cooked fast over high heat. The centuries-old practice hasn't changed much, but you can now purchase an electric rotisserie attachment to clip on the grill and rotate the meat, rather than the traditional method of turning a spit with a hand crank over an open fire.
Preheat your grill on medium heat or about 325 degrees Fahrenheit. Place a pan under the rotisserie spit to catch the drippings from the roast. If desired, add a small amount of water and either apple wood, hickory or mesquite chips to the pan to give the roast a smokey flavor.
Set the bottom round roast on a cutting board. Trim away any hard fat from the outside of the bottom round roast with a knife. You can trim soft fat too, but it helps flavor the meat and keeps it moist while cooking. If you don't want to eat the soft fat, simply trim it away before serving.
Season the roast with your choice of herbs and spices. Stick with basic salt and pepper, or try a spice rub with a blend of spices that you massage into the meat. Try spices such as garlic powder, onion powder, dry mustard, ground oregano, paprika, crushed red pepper or coriander.
Roll the roast into a uniform, cylindrical shape so it cooks evenly on all sides. Tie the roast with butcher's twine spaced every 1.5 inches along the roast; cut the excess twine off with scissors.
Push the rotisserie spit through the center of the bottom round roast. Secure the roast to the spit rod with spit forks. Push the spit forks into each end of the roast; tighten the lock nut down to lock the forks in place.
Line up the ends of the spit rod with the motor on the rotisserie rack. Turn the rotisserie motor on and close the hood of the grill.
Grill the roast for about 15 minutes per pound; total cooking time depends on the size of the roast and the actual temperature of the heat source. If desired, you can baste the meat periodically with a wet mop sauce, such as a blend of cider vinegar, cooking oil and spices.
Insert a meat thermometer into the center of the roast about 10 minutes before the end of your estimated cooking time to avoid overcooking. Remove the roast when it reaches the desired temperature. The roast is cooked to medium with an internal temperature between 125 F and 130 F, medium-well roasts are between 130 F and 135 F, while a well done roast should be cooked to at least 140 F.
Remove the spit from the grill and allow it to rest for at least 5 minutes before you remove the spit from the center and carve the roast. This rest period allows time for the juices to redistribute throughout the meat. If you pulled out the spit right away or carved it right away, most of the flavorful meat juices spill out on your plate instead of staying in the meat.