In a medium saucepan, combine 1 cup water and sugar over medium-high heat. Cook, stirring until sugar is dissolved. Stop stirring, and bring to a boil. Reduce to a simmer and cook for 5 minutes. Let stand until room temperature.
Prepare an ice bath.
Combine grapes and ¼ cup water in a medium saucepan. Cook over medium-high heat until the liquid begins to bubble and grapes start releasing liquid, about 4 minutes. Reduce heat, and simmer until juices are dark purple and grapes begin to break apart, about 3 minutes.
Pass mixture through a food mill and then through a fine sieve into a large bowl.
Set in the ice bath; stir frequently until completely cool. Stir in simple syrup and lemon juice.
Transfer mixture into an ice-cream maker, and mix according to manufacturer’s instructions.
Store in the freezer until ready to serve, up to 2 weeks.
Recipe by Kuhn Orchards at https://kuhnorchards.com/concord-grape-sorbet/