Add the remaining 1 tablespoon oil to the pot and then add the onion and pepper. Reduce the heat to medium and cook for 7 to 8 minutes, until slightly softened. Add the garlic and cook for 2 more minutes, until fragrant. Stir in the beer, tomato sauce, vinegar, tomato paste, cumin, paprika, sugar, 1 tablespoon salt, pepper, and cilantro. Return the beef to the pot and mix well. Cover the pot and simmer over very low heat for 2 to 2 1/2 hours, until the meat is fork-tender. Use two forks to shred the meat in the sauce.