Combine marinade ingredients into a large saucepan. Bring marinade to a boil while stirring and remove the pan from the heat. Using a blender, puree marinade. May need 2 batches. Transfer marinade to a bowl and let cool to room temperature. Spoon off any remaining foam.

Combine pork and marinade into large, heavy resealable plastic bag and press out any air. Put bag in baking dish and refrigerate for at least 8 hours and up to 24 hours. Turn bag once or twice during refrigeration. Remove from refrigerator and let pork come to room temperature (approximately 40 minutes). Transfer marinade to a saucepan and bring just to boil.

Preheat oven to 375 degrees F.

Pat pork dry with paper towels and season with salt and pepper. In a flameproof roasting pan, heat oil over moderately high heat (not smoking) and brown pork on all sides. Roast pork while basting frequently with some marinade until temperature reaches 155 degrees F. For slightly pink meat roast for 1 to 1 1/2 hours. Transfer pork to a cutting board while keeping the juices in the roasting pan. Discard string and let stand covered loosely with foil for approximately 15 minutes.

While pork is standing, skim and discard fat form pan and add remaining marinade. Deglaze roasting pan over moderately high heat, scrapping up brown bits. Bring sauce just to a boil and strain through a fine sieve into another saucepan. Bring sauce to a simmer and whisk in Beurre Manie in small increments, whisking until sauce is combined well and thickened slightly.

Serve pork sliced with sauce and a glass of Löwenbräu.