A few questions for my 15 lb brisket on mes 30:
1. What is a general rule of thumb for per lb time if cooking at 225 unwrapped?
2. What shelf would you put it on low middle high?
3. I'd like to try a longer rest this time....6 plus hours, what temp does it need to cool to, to stop cooking?
I smoke briskets unwrapped the entire time at a steady 275F (Auber PID controller on my MES40), also with a fan circulating smoke and air inside, and it takes me a like 1hr 5-10min per pound.
I place a standard foil pan (not a big-big one) on bottom rack. I then put an MES rack directly on top of the pan and I put the brisket on the rack. 80-90% of the brisket drippings make it into the pan even though there may be no real drippings at the end it keeps my MES from being a total mess.
So for a 15 pound brisket I would estimate about 16.5 hours for the meat to be close to probing tender (only done when tender) in my setup at 275F.
I add 4 hours to 16.5 for a total time of 20.5 hours.
So I expect that when I put my brisket into my pre heated smoker that 20.5 hours later I will be slicing, serving, and eating it.
Why add 4 hours?? Buffer time.
If it finishes 4 hours early then EXCELLENT! I tightly double wrap in foil then tightly wrap in 3 bath towels and place on the table/counter for a 4 hour rest where it is piping hot ready to serve 4 hours later.
If it doesn't finish 4 hours early.... I have 4 hours of extra time for it to get done before people attack me with forks and knives.
Win-win.
Understand that briskets don't care what temp you cook them at as long as you aren't burning them. So I would recommend maxing out your MES40 at 275F knowing that it likely will never reach that max temp so maybe you get 250F end the end which is better than 225F.
Just try and give yourself a best guess as to what temp your MES may actually hit.
Figure out roughly how many hours per pound it takes at that time then add 4-6 hours of buffer.
Start that many hours before you plan to eat and you are greatly increasing your chances of a successful brisket smoke :)