Remove the grapes from the stems and rinse well. Place them in a medium mixing bowl and pour the lime juice over top. Stir to coat.
Place the grapes in the fridge for about 10 minutes. While grapes rest, whisk together the monk fruit sugar and citric acid in a small bowl. Set aside.
Strain the grapes in a colander. Then, transfer half of the grapes to a fine mesh sieve. Pour half of the monk fruit mixture over the grapes and sift over the baking sheet. Dump the grapes onto the pan. Repeat with the remaining grapes and sugar.
Roll the grapes around in the sugar on the pan to make sure they're completely coated.
Chill the grapes for 2 hours. Then, transfer them to a bowl and enjoy cold!
Notes
Citric acid is what makes the grapes sour. If you like REALLY sour things, you can add more (½ to 1 teaspoon at a time) until your desired level of sourness is reached.
The carbs listed for each 0.25 cup of grapes is 14 grams. The monk fruit sugar contains Erythritol. After subtracting the sugar alcohols, each serving has a net carb amount of 8 grams.