Brown ribs in slow cooker pot (or skillet) on top of range over medium heat. Season with salt and pepper. Transfer cooker pot to base unit or meat from skillet into cooker pot. Layer sauerkraut, onion, mushrooms, apple wedges and brown sugar over ribs. Sprinkle with celery seed. Cover and cook on low for 7-9 hours or on high for 3-4 hours until meat is tender.