> A search of this group on Google yields a number of threads on this
> subject. It seems that a slow starting and slow fermenting Ribena must
> is a common thing. It might be best to repitch yeast, if not already
> done, and let it go. It'll either ferment or rot. No reason to throw it
> out until you know for sure.

I wouldn't throw it out unless the cost is minor but the benzoate is
going to be an issue. Maybe diluting it enough to get it to start and
feeding the remaining in might be the best option. If you are
concerned about spoilage you could take what you have now and freeze it
in gallon bags; then thaw a gallon at a time to add it back in.

I might start like this.

Take 1/10 of what you have and dilute it with 5 to 10 parts water and
enough sugar to get that to a SG of 1.070. See if that will ferment.
If not, find another use for the remaining batch. Assuming it gets
going, once you have a decent ferment add back into it the same amount
of Ribena you started with and see what happens. Go slow and keep the
fermentation temperature over 70 F.

I am making this up; I have no experience doing this by the way...
That is what I would try if i were you though. You do have to be very
careful of using anything with preservatives, they are in there to
retard fermentation among other things but you know that now.

Joe