So I cobbled together a few ideas from my research, and I am very pleased with the resulting recipe! I've been talking tomatoes with a number of people recently, and several are interested in this specific recipe.
Yield: approximately 5 half-pints
6 lbs. tomatoes
2 medium onions
2/3 cup apple cider vinegar
1/3 cup brown sugar
2 1/2 tsp. salt
1-2 whole cloves
pinch celery seeds
3 Tbsp. corn syrup
2 Tbsp. cook-type Clear Jel
Core tomatoes. Peel onions. Chop roughly. Puree tomatoes and onions in food processor. Place in 6 quart slow cooker on high with lid on for 1-2 hours. Stir in vinegar, sugar, and salt. Place spices in tea ball or cheesecloth bag and add to mixture. Cook on low or high for about 8 hours with lid removed or cocked until significantly reduced and thickened. Avoid stirring, which slows down the evaporation. Remove spices. May puree ketchup with immersion blender here (I do). Separately, mix Clear Jel with corn syrup. Whisk into hot ketchup very slowly and thoroughly. Cook for another hour or so with lid off, stirring often, until thick and glossy. Taste for balance of sweetness, saltiness, and sour. Adjust. Process half-pint jars in water-bath canner for 30 minutes to seal (pints 35 minutes).
|tomato jam, salsa, ketchup, tomato soup base, pizza sauce
Note: You could cook the tomatoes and onions together first until they're soft, then put them through a food mill. This effectively removes all skins and seeds. I puree mine pretty well, but there will be an occasional seed floating through the ketchup. I'll trade that for the efficiency of the food processor any day.
Note: All slow cookers vary, which is why I say "low or high" with "lid removed or cocked." If you've never tried to reduce liquids in your slow cooker before, you're going to have to pay attention the first time. The ketchup will not scorch - that's the beauty of a slow cooker over the stovetop method.
Note: Clear Jel is usually approved for canning. Cornstarch and flour are not approved for use in canning (although there are some people who feel comfortable canning with them). Do not decrease the processing time. Alternately, you could simply refrigerate the ketchup.