14 - 16 lb turkey
1 cup kosher salt
1/2 cup light brown sugar
1 gallon vegetable stock
1 tablespoon black peppercorns
1 1/2 teaspoons allspice berries
1 1/2 teaspoons chopped candied ginger
1 gallon heavily iced water
2 to 3 days before roasting:
Begin thawing the turkey in the refrigerator.
Combine the vegetable stock, salt, brown sugar, peppercorns, allspice berries, and candied ginger in a large stockpot over medium-high heat. Stir occasionally to dissolve solids and bring to a boil. Then remove the brine from the heat, cool to room temperature, and refrigerate.
Early on the day or the night before you'd like to eat:
Combine the brine, water and ice in the 5-gallon bucket. Place the thawed turkey (with innards removed) breast side down in brine. If necessary, weigh down the bird to ensure it is fully immersed, cover, and refrigerate or set in cool area for 8 to 16 hours, turning the bird once half way through brining.
2/3 cup barley malt syrup
1/4 cup malt vinegar or apple cider vinegar
6 fresh sage sprigs
4 fresh thyme sprigs
1/2 teaspoon ground black pepper
2 tablespoons (1/4 stick) unsalted butter
Bring malt syrup, vinegar, herbs, and pepper to boil in small saucepan, stirring occasionally. Reduce heat to low and simmer until glaze coats spoon, 4 to 5 minutes. Mix in butter. DO AHEAD Can be made 1 day ahead. Cover; chill. Rewarm before using.
Remove turkey from brine. Pat very dry, inside and out, with paper towels. Sprinkle main cavity with 2 teaspoons pepper; fill with onions, celery, sage, thyme, and garlic. Close cavity with turkey lacing pins. Tuck wing tips under; brush all over with oil.
TO GRILL TURKEY
Prepare barbecue (medium heat). Remove top grill rack. If using charcoal, light briquettes in chimney. When briquettes are covered with white ash, push to opposite sides of bottom grill rack, leaving center empty. Place disposable aluminum pan in center of rack (you will need to light additional briquettes, checking every 30 minutes during grilling time). Replace top grill rack. If using 3-burner gas grill, light burners on left and right sides, leaving center burner off. If using 2-burner gas grill, light burner on 1 side; place disposable pan over unlit side.
Place turkey, breast side up, on grill rack over disposable pan. Cover barbecue. Insert instant-read thermometer into hole in hood. Maintain temperature as close as possible to 350°F on charcoal grill by opening vents to increase temperature and closing vents to reduce temperature or adjusting temperature on gas grill with controls. Cook turkey 2 hours, tenting loosely with foil if browning too quickly. Brush turkey with glaze. Cover grill; cook 30 minutes longer. Brush again with glaze. Cook until thermometer inserted into thickest part of thigh registers 165°F, about 30 minutes longer. Transfer turkey to platter. Brush with glaze. Let rest 30 minutes (temperature will rise 5 to 10 degrees).