In large bowl, toss grated cheese with the flour. In 2-quart saucepan over medium heat, swirl in the olive oil. When shimmering, add the garlic; cook 30 seconds until very fragrant. Add stout, apple juice concentrate, ground mustard and Worcestershire sauce. Heat to a simmer (let simmer 3 minutes if you want alcohol to evaporate) and gradually, in small batches, add cheese, constantly stirring until fondue is smooth, thick and cheese completely melted. If too thick, stir in an additional oz of stout until desired consistency.