In a small saucepan bring sugar and 1 cup water to a boil, stirring until sugar is dissolved, and stir in zest. Cool sugar syrup to room temperature. Transfer syrup to a small pitcher and stir in remaining 2 cups water, lemon juice, and mint. Chill lemonade until cold. (Makes about 4 1/2 cups lemonade.) Pour 1/4 cup lemonade, or to taste, into each of 4 chilled beer glasses and top off with beer.