Wash and dry the grapes.
In a saucepan or microwave safe bowl, combine the vinegar, sugar, and salt.
Bring the mixture to a boil, stirring to dissolve the sugar.
Remove from heat and let cool slightly.
Place the grapes in a jar or container and pour the vinegar mixture over them to cover.
Refrigerate for at least 2 hours, or up to 1 week.
