Bring a large pot of water to a boil. Blanch the tomatoes by dropping them in the boiling water for 1 to 2 minutes. You will need to do them in batches. Transfer the tomatoes to a sink or tub filled with cold water.
Peel the tomatoes, and chop them coarsely. If you can remove some of the seeds as you go, this will help. Layer the tomatoes in a large strainer - such as comes in a set for cooking spaghetti - with the salt. I try to use about 4 tablespoons, but a bit more is okay. Much of it will run out with the water. Let the tomatoes drain for several hours to overnight, in a cool spot. (Not in the fridge.) Don't forget to keep them a little raised from the bottom of whatever pot you strain them into, so they are not sitting in their own water. Ideally, do this the night before you plan to proceed.
Meanwhile, deseed and mince the peppers. Peel and mince the shallots and garlic. Put them in the preserving kettle with 1 cup of the vinegar. Add the drained tomatoes when you have strained them for as long as you can stand. Bring to a boil and simmer for 30 minutes, until the vegetables are tender.
Press the mixture through a fairly fine food mill. Discard any seeds and skins that will not go through. You will likely need to stop and clean the mill once or twice during the process. Return the pulp to the stove, and add the remaining vinegar, and the Sucanat.
Grind the celery seed to a powder, and mix it into the ketchup with the two paprikas and the ginger. The peppercorns and allspice should be tied up in cheesecloth, or put in a very large tea-ball and added to the ketchup. Boil the ketchup, stirring frequently, until considerably reduced in volume and very thick. Expect this to take about 2 hours.
About 45 minutes before you expect the ketchup to be thick enough to bottle, put the canning jars into a large canner with water to cover them by one inch at least, and bring to a boil. Boil the jars for 10 minutes. If your water is very hard, add a shot of vinegar to the water to prevent lime build-up on the jars.
When the ketchup is thick, test it and adjust the salt and seasonings if necessary. Remove the black peppercorns and allspice, and discard them.
Fill the jars with the ketchup to within 1 cm of the rims. Seal with lids and rims which have been boiled for 5 minutes. Return the jars of ketchup to the boiling water bath and boil for 10 minutes.
Remove them from the canner, allow to cool, check the seals, label and store. Keep in the fridge once opened.