I had a 13 pound select and a 15 pound choice in the fridge that I cooked yesterday. I needed some cooked freezer meet for "rainy days" and of course some of it was for weekend eats. Trimmed them both up very aggressively Friday night and put them on around 3AM Saturday morning.
Part of the cook was a test. The question comes up a lot about using charcoal in a stick burner, so I decided to see how far I could push it. I have used charcoal plenty of times both as a bed for my splits and as the only fuel. It is not nearly as efficient as it is be in a WSM or UDS despite the fact that I have a charcoal basket for just such use. The amount of airflow needed to keep an offset at temp is way more than that needed for a drum/bullet, so the coal burns down far faster. My charcoal basket will hold 2 20 lb bags of charcoal, but for this test I just loaded it (packed tight around the basket) with one full bag of KBB (will get a longer burn with briquettes than lump). I inserted a can with both ends cut off in one of the corners (rectangular basket) of the basket closest to the firebox door and filled around it. I lit 13 coals and dropped them in the can then lifted it out of place to start the fire for kind of a Minion burn.
I was up to 200 degrees in about 15 minutes and loaded the meat while leaving the dampers open to get the temp up. At 275, I started choking the dampers until I found the spot where I could hold 280-300 consistently. I was only heating the main chamber of the offset. The warmer box was cut off. The test went surprisingly well in terms of temp consistency. After a couple of micro adjustments to the intake dampers I was able to hold temp for four hours with no spikes taking me over 320. I have got the main chamber of this smoker over 500 before with just charcoal in the firebox when too much gets lit, but this lit slowly and consistently. That much coal getting lit at once was a concern. The time I was able to run on that one load was as expected shorter than I would need for a cook that large, but I would not want to waste that much charcoal on a small cook. I might try the test with 2 full bags loaded (I still have a $hit ton of KBB from the $4.99 for 2X20 bags sale that some of use were able to get last summer). I am not sure if having that much extra charcoal in the box is going to cause too much to light at once and turn my offset into a grill even with a Minion burn. I could set up dividers to make it snake better, but honestly it isn't worth the trouble. The bottom line is... to answer the question of how long can you ignore an offset cooking with charcoal, I could have taken a couple of hour nap and done other stuff for probably 3.5 hours worth of the cook instead of having to feed spits.
I ended up loading splits from the 4 hour mark until the end using what little charcoal was still lit at four hours to lite the splits, though I could have held temp for another half hour to 45 minutes if the cook was nearing an end. So I probably could have got five solid hours on just a bag of charcoal. YMMV on a less efficient cooker without a charcoal box that is very close to the main chamber when inserted. My tuning plates keep the fire indirect, because without them it would be a grill on the right side of the cooking area.
The larger choice actually finished 1/2 hour quicker than the select despite pretty consistent L>R grate temps. It probed easily and was also reading a higher internal temp earlier than the smaller brisket. Just goes to show you that no two pieces of meat cook the same. I wrapped both in BP when I moved from charcoal to splits. The choice came off after 9 hours and the select after 9.5 hours.
Well, the finished brisket is kind of secondary at this point. Both turned out very nice with absolutely no difference in flavor and only a slightly backwards difference in cook logistics as the smaller one finished faster. Even the flavor profile was pretty near identical as when I cook packers with just splits. Since the only all wood part of this cook was while wrapped, the smoker flavor and ring came pretty much all from the KBB.
Choice after a few slices of flat are cut off.
Choice flat slice.
Select with point and flat separated.
Select flat slice.
