[DanB]

Originally Posted by SmoothBoarBBQ

As others have said you've undercooked the meat and that's why it's tough and chewy. Your stated plan for next week sounds pretty good, but I wouldn't worry about waiting until it comes all the way down to 140° before you start slicing it up. Putting the brisket in an ice chest is really only something you should do if you want to HOLD the meat, rather than rest it. Holding will keep it hot for several hours, while resting it slowly allows the meat to reduce from ~200° to a more edible temperature. If you're close to ready to eating when the brisket is nice and tender then let it REST, on the counter, loosely tented in foil for maybe 35-45 minutes.

The "probe test" is the most effective means at determining the doneness of a piece of meat. Temp is a good guide but as others have stated large cuts of meat can have huge spans of finishing temps....from 190-215°. People say butter but for people who are trying to figure out what that means I suggest using a jar of peanut butter rather than a stick of butter. Before you probe the meat stick the probe into some peanut butter and get a feel for that resistance...that's going to be just about right in terms of how the brisket should feel when you probe it. Mind you I'm talking about the flat, not the point. You can cook it a bit further and get closer to butter, but butter has no resistance and when you take a brisket that far you're going to end up with some crumbling...which is OK because it's still good.

Also, Lang's are Reverse Flow cookers, so your entire cooking chamber should be VERY close in temp...probably 5° left to right. So no need to get in there and rotate the meat...just leave it alone, leave the door closed, and run a clean fire.

Good luck with your next cook and post your results (with some pics), and this way if you're still having problems we can try and give you a bit more guidance.

Probe it, can't go wrong!!
DanB