Am I allowed to add flavor juice to the Revi’is Kiddush (dry) wine?
One may only add water to the extent that the wine – or grape juice – can still be drunk as wine and served to guests that way.
Regardless, the water may never be 85.7% or more in the mixture (assuming no water was added by the company). One should ideally machmir that the water should always be less than 75%.
Regarding adding other drinks, they may not be more than 50%.
Sources – See here: