Even when wine is guaranteed to contain no gluten, it may not be gluten-free. What's the catch? Although the grapes used to make any wine naturally contain no gluten, environmental contaminants that do contain gluten still can end up in the product.
If you have celiac disease or another medical condition that precludes your consuming gluten, select wines that are gluten-free. As in the case of gluten-free foods and other beverages like gluten-free beer, taste is subjective. Some folks don't taste a difference at all; others do. You be the judge.