Guinness stout is definitely a bitter beer and can add a strong bite to this dish. Some folks are opposed to the earthy and complex flavors of dark beer. Others find it delicious. If you'd rather not use beer in this recipe, feel free to add more beef stock or broth as a substitute. If you make this dish with Guinness and it's too strong for your taste, add a little bit of brown sugar to the pot to balance out the bitterness.