As with all BBQing, there is no 1 perfect way to cook a brisket. Here is a post I made to another board where I was asked how to cook a brisket.
Hope it helps someone!
Brisket is about the hardest meat to get exactly correct..at least when competing. The judging test is as follows........slice a piece about 1/4-3/8" thick(NO thicker!). Then, hold between thumb and forefinger in each hand. At this point the meat must stay in one piece. Next, pull the meat apart by gently tugging it. It should separate with little effort. That is VERY hard to do!
There are so many ways to cook a brisket, but low and slow is where you must start. Most competitors will cook the entire brisket, many do NO trimming whatsoever to their Packer cuts. When finished cooking, they will cut very select pieces from the flat to turn in to the judges.
Now, I learned to cook brisket using the whole cut...flat and point. The point always takes longer to cook(twice as thick as the flat), so you will end up separating the flat and putting the point back on the smoker for another couple of hours.
Since those many years ago, I now separate the point from the flat BEFORE cooking and cook each piece separately. Nowadays, most of the time I buy only the flat, especially when catering. Sam's carries them in Choice grades for a very good price and the entire fat cap is intact. Avoid the cheapies at Wally World as they will be Select grade.
Fat side up or down??? That is changing in the last 2 years. Used to be everybody did them fat side up. Now, many will flip them half way thru the cook. The theory is that they will simmer in their own fat when the fat side is down.
To trim or not? I have cooked brisket every which way including trimming ALL the fat cap and then using toothpicks to secure back in place. Why do this? There is NO spice on Earth that will penetrate a fat cap. So, I cut it off, season the meat and then replace it. Lots of work, but effective.
My most recent method is to leave the entire fat cap in place with NO seasoning on that side of the meat and then AFTER it reaches my internal temp and BEFORE I rest it, scrape that fat off and season that side. Then rest for about an hour or 2. Much easier and much more flavor.
If you decide to trim, you are walking a fine line between trimming too much and not enough. Your type of smoker will make a difference as well. Water units will NOT melt that fat cap..even just 1/4" of it. Whereas, the offsets will melt most of it away.
Timing? I have had briskets cook in as little as 45 min/lb. and take as long as 2 1/2 hrs/lb. The difference? THICKNESS. The weight is important for timing, but the thickness is the key. Briskets come in greatly different sizes, so you must pay attention to the thickness. Sorry, no general rules as to this, just experiment and take good notes.
Foil or not? Again, no 1 correct way to do this. In the early 90's the winningest brisket cook foiled his briskets when they hit 165?, let them cook to about 188-190?, remove and let rest for 1 hour. Today, the best brisket cook does NO foiling, except at the end to let it rest.
Final temp? It has to be above 180?, but below 200?. Too low and it will still be tough, too high and you have yourself pot roast and it falls apart. No such thing as Rare, Medium or Well Done!
You should try and avoid using foil at the start of the cooking process. This will prevent any type of bark from forming and like other BBQ, the bark is where the flavor is most intensified. I like to layer my seasonings and always apply more rub after mopping.
Me personally, I have won with foil and without foil. The one common thread is near the end let it rest for at least 1 hour. Foil it, wrap in towels and place in a dry cooler. Be sure to KEEP the juices and add them to your sauce.
I spend more time working on these things than any other cut, but I've also found the more time I spend and the more careful I am, the better the product turns out.