We have oodles of concord grapes around our property and around our generous neighbor's. I've made jam, but thought I'd try something different. Per request, here's the recipe I used. It's not really from a source, it's created by me after researching oodles of recipes and figuring out what works. My kids love it on eggs, as a dipping sauce and as topping. It also would be good for a sweet/sour meatball type of meal.
Grape Ketchup by Jackie
4 pounds concord grapes
4 cups apple cider vinegar (I used my own homemade version)
6 cups sugar
2 T cinnamon
1 T allspice
6oz tomato paste
1) Steam grapes using 1 cup of water until softened. Mash grapes, strain juice, discard skins and seeds.
2) Place grape juice in saucepan, add vinegar, sugar, cinnamon, allspice. Bring to boil. Simmer for a few hours stirring periodically or until has reduced by half it's amount. (Or you could leave in a crockpot with the top cracked for 24 hours).
3) Whisk in tomato paste. Let reduce further until the consistency is ketchup-like.
4) Waterbath can for 15min.