Prep the loin: Rinse the pork loin and trim any excess fat, leaving ⅛" to ¼" thick layer and scoring it down to the meat every ¼ inch. If necessary to fit in your roasting pan, cut the loin in half.
Make the wet rub: In a small bowl, mix the celery salt, onion & garlic powders, Worcestershire sauce. Add water ½ teaspoon at a time to loosen the mixture up and form a paste.
Rub the paste all over the loin, working it into the scored fat, and refrigerate overnight.
Preheat smoker (or oven) to 275-300 degrees. Meanwhile, on the stove, heat a heavy roasting pan or dutch oven on high for 4-5 minutes. Drizzle a little olive oil in and put the loin in, fat side up. Sear all sides well, including the ends.
When it's nicely browned all over, remove the loin to a platter. Deglaze the pan with ½ of the beer to free up all the good bits on the bottom. Add one bag of sauerkraut, including liquid and turn off the burner.
Return the loin to the pan, on top of the 'kraut with the fat side up. Drain the other bag of 'kraut, reserving the liquid, and arrange it around the loin.
Place pan into smoker (or oven) and cook to an internal temp of at 150, about 2 hours.
Remove from smoker, cover tightly and let rest for at least 30 minutes or up to an hour. Slice and serve with sauerkraut and mashed potatoes.
