Hi Burch,
I made a gallon jug of the Welchs Niagara, this is what I did and it came out very good.
Recipe:
12/18/09
3 cans welchs niagrag
1 cup of sugar (sg 1.090)
1 tsp yeast nutrient
water to 1 gallon
yeast 71b 1122
Acid was .675%
1/29/10
racked, k-meta & sorbate, backsweeten to 1.020, I wanted to backsweeten to 1.010 but I added too much sugar. I pulled juice out of the gallon and added sugar to that instead of a simple syrup, this is just my personal preference. I normally do this before it is completely clear. I was shooting for 1.010 but added to much sugar. If you do it this way, start with one cup of sugar to enough wine to disolve, warm it up but do not boil, let it cool and add back. Stir, then take an sg reading, if you are close take enough juice out and add 1/2 cup of sugar, process like before and take a reading. I was impatient and did not stir the wine well enough and added too much sugar the second time around but it was still very tasty. Niagara I think is good as a sweet wine.