I just picked up a couple of bottles of Manischevitz Concord (NOT a recommendation) and noted that it is at least 51% concord. Anyone have any idea what the heck the other 49% could be?
Domain du Castel. The red is probably the best Kosher wine made in Israel. I do not like the white as much. If you want Bordeaux, Haut Condissas and Rolland de By make Kosher cuvees that are not horrible. Guiraud for the sweet lovers who want to step up from Manischewitz. If you can get the 2001 Guiraud, it is outstanding. The kosher is better than the regular cuvee because coincidentally the day they chose to pick the kosher was the perfect day for picking. It is a 95+ point Sauterne, but very hard to find these days. Capcanes also makes a reasonable Kosher wine in Spain. The Leoville Poyferre, if they still make it, is GROSSLY over-priceed and I do not think it is worth it.
I have had very good results with Dalton from Galilee. The Pinot Gris & Petit Sirah have been impressive from a couple of vintages. Most I have tried have reflected their respective variety well. Although the Cab & the Shiraz from 2013 were too oaky for me.
If you buy Manischevitz, be careful that you are getting the Kosher for Passover version. For Passover, they add sugar to sweeten the wine. The rest of the year they add High Fructose Corn Syrup, which is not Kosher for Passover - similar to Coke.