Some sources say that carbon dioxide has no taste or smell but others say that it is acid/sour (this is the same word in German).

I think the latter are right in every aspect because if you open a bottle of sparkling water and let the gas above the water into your mouth it definitely tastes sour.

But why are there sources that say it has no taste or smell? Do they just mean you can't smell it in the concentration in which it is present in rather bad air? Or do they mean that the gas itself is neutral to our receptors, and they respond only to the carbic acid it forms with water? But it would be rather difficult to try to smell/taste DRY carbon dioxide, wouldn't it?