I don't think the tightness of the wrap matters, and I put mine in a pan and cover it with foil. This has several benefits:
- It ismuch easier than wrapping in foil;
- The pan catches all the juices;
- I can then simply put the pan into a cooler without having anything leak out of the foil
The main purpose of the wrap, I believe, is to stop "the stall" by preventing the pork from "sweating." I've read several scientific studies of what causes the stall, where the temperature stays at around 160 for many hours. From what I've read, it happens because the moisture escaping from the meat evaporates, thus cooling the meat at the same rate that the meat is taking in heat from the cooker. However, once you enclose the meat so the moisture can't escape, there is no more evaporation, no more evaporative cooling, and as a result the meat resumes its upward temperature climb. The meat will still exude moisture, which is the trapped in the pan, forming juices, but that released moisture no longer evaporates and cools.
I just re-read two experiments done by Cook's Illustrated (same people as America's Test Kitchen). The first one cooked two identical roasts, one at 450 degrees and the other at 250, this latter temperature being similar to many smoker temps. They were both cooked to the same final internal temperature. The high-temp roast lost 25% of its original weight, whereas the one cooked at the low temperature lost only 9.25%. This is a good argument for not cranking up the heat to get through "the stall."
In the second test they put several roasts into sealed vacuum bags, some with no liquid, and the others filled with varying amounts of braising liquid. They put the sealed bags into 190 degree water and cooked them for almost two hours. At the end of the cooking time, when they measured the liquid, the increase in liquid (i.e., the liquid that came out of the meat) was absolutely identical, whether the meat was immersed in liquid, or whether the bag was dry.
So, if I am to believe these tests, the moisture lost from the meat will not be slowed or diminished by wrapping, but WILL be slowed by keeping the temperature down.
Finally, this same group has done all sorts of other tests about resting meat after cooking. Most of the pulled pork recipes call for putting the pork into a cooler for one or more hours. The Cook's Illustrated tests showed that this resting time does indeed help the meat to reabsorb some of the liquid.
So, my conclusion:
- Wrap the meat to get through the stall, but don't expect that to make it more moist;
- Resist the temptation to crank up the heat to get through the stall;
- Let the meat sit for a long time before pulling.
Of course there is one more thing these tests didn't reveal, because they weren't dealing with a long smoke, and that is the formation of bark. It is pretty clear that the sooner you wrap, the less bark you are going to get. And, that is where experience comes in. I am a novice at smoking, so I can't comment at all on that, and I haven't seen any scientific experiments to guide me.
That's why I read as many of the posts in this forum as I can.