Slow-Cooker Size: 6-quart
Place ribs in a large shallow dish or zip-top freezer bag.
Combine juice concentrate and next 6 ingredients in a small bowl with a wire whisk. Reserve 3/4 cup mixture in refrigerator for dipping. Pour remaining mixture evenly over ribs; cover or seal, and chill 8 hours, turning occasionally.
Remove ribs from marinade, discarding marinade. Place 1 rack of ribs in bottom of a 6-quart slow cooker; stand remaining rib racks on their sides around edges of slow cooker. Cover and cook on HIGH 1 hour. Reduce heat to LOW, and cook 5 hours.
Microwave reserved 3/4 cup sauce in a 1-cup glass measure at HIGH 1 to 1 1/2 minutes or until thoroughly heated, stirring once. Serve with ribs. Garnish, if desired.
Stand Your Ribs: Standing these ribs along the sides of your slow cooker gives them direct contact with heat, so they'll have crispy brown edges like ribs that have smoked for hours.