I just walked my neighbor through how to do this on his very first brisket, with a borrowed smoker no less, and it turned out excellent.
First (assuming you’re cooking a whole packer), trim all the thick hunks of fat completely from the brisket. Get down to bare meat. Then, trim the fat cap down to no more than a quarter-inch. You really can’t trim a whole packer too much. There will still be plenty of fat to keep it moist, even if you trim very aggressively.
Next, apply rub liberally to the entire brisket. I don’t inject, even on my contest briskets, but if you want to, now is the time. Wrap brisket in two layers of plastic wrap and rest in the fridge for at least 8 hours.
After the brisket has rested sufficiently, fire up your smoker to around 250º. Once your smoker has come up to temp and is running cleanly, remove your brisket from the fridge and place it directly on the hot grill. Do not let it come to room temp. Place the brisket fat cap side down with the point end pointed toward the hot side of the grill and the flat away from the hot side. Close the lid and leave it closed for at least 4 hours.
After 4 hours, crack the lid quickly to check on the brisket. Rotate, or move it around if necessary. Shut the lid.
After another two hours, open the pit and check the temp of the flat. Once the flat hits 165º, quickly pull the brisket from the pit, wrap loosely in two layers of heavy duty aluminum foil and place it back on the pit. I’m very careful when I wrap my briskets to not wrap them too tight. Basically, I stretch out one layer of HD alum. foil, set the brisket fat side down in the middle of the sheet, then working clockwise (or counter clockwise, direction doesn’t matter), fold each side of the foil up over the top of the brisket, in overlapping layers. I never crimp the foil so it’s air tight. I like to let some steam escape. Then, I stretch out one more sheet of foil and set the wrapped brisket on top of it and use that bottom sheet to lift/move the brisket around. During this time, I also add a can of Campbell’s beef consume to the foil before I wrap it up.
Set your wrapped brisket back on the pit carefully and continue cooking for another 1½ - 2 hours. Then, gently open up the top of the foil and check the brisket flat for tenderness. If it’s not ready, just push the foil back down and cook for another 30 minutes then check again. When the flat finally feels tender, I like to open up the foil and leave it open for another 15-20 minutes before I take the brisket off the pit to tighten up the bark. Then, remove the brisket, with the foil still open and set it aside to rest. While resting, I will close the foil part way, so it will still vent but also not cool too quickly. It’s at this point, you can separate the brisket point from the flat, apply some more rub on the ‘scab’ and put the point back on the grill naked for another 1-2 hours to finish rendering the fat in the point for the best damn burnt ends you’ll ever have.
As far as slicing goes, only slice a well-rested brisket. As others have said, rest for at least one hour. If I have the time, I’ll rest it until it’s cooled down to 140º, the I’ll refrigerate it overnight, still in the same foil it cooked in. Then, I’ll slice it cold the next day and reheat in the oven in a tightly covered pan.
Hope this helps, good luck!
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