dcbowers said:
This is a hotly debated topic.
However, the theoretical rationale that fat side up causes gravity to pull the fat and moisture into the brisket is false. On the other hand, fat side up separates the seasonings from the brisket and may decrease flavor. I always do fat side down.
I agree that fat up doesn't cause gravity to pull fat and moisture INTO the interior of the brisket, but I believe it does allow some fatty moisture to remain ON TOP of the brisket to keep the bark more flavorful.
I don't see how fat up would "separate the seasonings from the brisket and reduce flavor" any more than fat underneath rendering and immediately dripping off the brisket into the smoker from upside down, taking some seasoning with it. Seems logical to me that way would be more likely to remove seasonings.
I always apply my rub a day in advance of smoking to dry brine and allow the salt to penetrate through osmosis. This gives the salt, pepper and other seasonings a chance to really adhere to the meat and help form a crust during smoking.
The one possible advantage I can see to fat down is maybe it helps insulate the bottom of the brisket for smokers with heat rising from directly below as mentioned. But even then, I personally think if there is a difference it's very minimal.
I personally believe if you've selected a good brisket to begin with (which will have a lot of internal fat) and trim it properly so the smoke and seasonings can better penetrate the meat, it doesn't matter which side is up. I'm certainly open to being shown the error in my ways and always willing to try new things to improve though.