A bitter drink for bitter people.
--Pseudo_Intellectual

Actually, if you believe the label, their slogan is: A delicious non alcoholic beverage

I'm not sure what "Brio is produced from a secret blend of fruits and herbs" actually means, but the ingredients aren't so secret that they don't put them on the label. They are: Carbonated Water, Sugar, Caramel, Natural Flavours, Phosphoric Acid, Sodium Benzoate, and get this Quinine.

At least now we know where the bitterness comes from.