Combine first 6 ingredients in a 5-quart slow cooker; stir in pieces of roast. Microwave beer in a 2-cup glass measuring cup on HIGH 2 minutes or until very hot. Pour beer over meat in slow cooker; do not stir. Cover and cook on HIGH for 6 hours or until very tender.
Shred meat using 2 forks. Serve hot or see notes below.
* We used adobo sauce from canned chipotle chiles in adobo sauce.
Make-Ahead Note: Transfer meat mixture and juices to a 13" x 9" baking dish; cover and chill overnight. To reheat, crumble meat mixture into a large skillet, and cook over medium-high heat 15 minutes or until browned and hot.
Microwave Option: Traditionally, Carnitas are browned in their own drippings until they are crisped and browned. However, reheating the shredded pork in the microwave is an easy alternative. Microwave 6 cups meat mixture on HIGH 6 minutes, stirring once, or until thoroughly heated.