The farther back on a cow's body, the more tender the meat, and sirloin is in the heart of the most tender portion of the animal. However, the sirloin tip cut contains little fat marbling and some connective tissue, making it leaner but also a challenge for smoking. Barbecue enthusiasts usually select fattier meats for smoking because the fat naturally bastes the meat during the long cooking process, keeping it moist. But smoking a juicy, flavorful sirloin tip on your backyard barbecue is possible if you properly season the roast through a process called dry-rub curing.
Before Starting the Fire
Mix all seasonings thoroughly in a small plastic bowl, using a fork to break up any clumps and blend the spices. The mixture becomes your dry rub.
Place the roast on a clean cooking sheet and coat it generously with the dry rub. Work the spices into the meat and create a thin layer of seasoning across all meat surfaces.
Cover the seasoned roast with plastic wrap and refrigerate overnight prior to smoking.
Dump all wood chips into a plastic bowl or bucket and fill the container with enough water to either submerge or float all of the chips. Soak the chips for at least an hour prior to smoking time.
Smoking the Meat
Open all grill and firebox vents and chimneys wide for maximum air flow. Remove and set aside the cooking grate from the main grilling chamber.
Place five or six large handfuls of natural lump charcoal into the chimney charcoal starter. Stuff two crumpled-up sheets of newspaper into the lower chamber of the starter.
Place the chimney starter on the coal grate -- the lower one -- of the main grilling chamber. Light the newspaper from underneath using a long butane grill lighter or stick match. Give the coals about 20 minutes to thoroughly ignite.
Dump the lit coals into the side firebox and close the hatch. Place the foil roasting pan atop the coal grate of the main grilling chamber. Position the cooking grate back on the grill.
Place the cured beef roast on the cooking grate directly above the foil roasting pan so that all drippings during the cooking process fall into the pan. Close the grill lid.
Toss a handful of soaked wood chips atop the lit coals inside the firebox and close the hatch. Wait about 20 minutes for the temperature in the main grilling chamber to reach between 250 and 300 degrees, then adjust the firebox and chimney vents to maintain this temperature consistently throughout cooking.
Add two handfuls of charcoal every hour and a handful of wood chips every 30 minutes to maintain heat and smoke. A 5-pound beef roast takes five to seven hours using this method, depending on the effects of outdoor temperature and wind speed on the temperature in the grilling chamber.
Avoid opening the main grill lid for frequent checks of the meat. This releases precious heat and smoke, causing the meat to cook unevenly or extending the smoking time. Don't skip the wood-chip soaking process. Wet wood chips smolder rather than quickly burning up, producing more smoke, which is the heart of the flavoring process.
Always use protective mitts or grilling gloves when handling hot grill lids, firebox hatches and vents to avoid burns. Use long-handled utensils to move meat to or from the hot grill.