I think we can state without doubt that red grapes don't have gluten.

I'm also wondering if there isn't a different reason that this person can't have red grapes/wine. Multiple allergies are so common, and it might be this person just throws in 'red grapes' when talking about what she can't have?

Maybe someone needed to pass on "wine" for other reasons and felt it easier to say they can't have wine because red grapes have gluten? Maybe even as a joke?

Cara