1.
Grate the zucchini and mix with the salt.
2.
Cover and let sit for at least 1 day, then pour off the liquid and squeeze the zucchini well.
3.
Coarsely chop the tomatoes and onions and place on a baking tray.
4.
Sprinkle with 2-3 tablespoons of raw cane sugar and some salt.
5.
Bake in the oven at 250°C top and bottom heat until soft (approx. 30–45 min).
6.
Let the mixture cool and then pass through a food mill to remove skins and seeds.
7.
Put all ingredients together in a large pot and simmer for 2 hours.
8.
Blend or purée the mixture to achieve a smooth ketchup consistency.
9.
Depending on the ketchup consistency, reduce the mixture a little more on the stove.
10.
This recipe yields about 3.5 liters of ketchup at the end.
11.
Sterilize jars or bottles (ideally not too large jars with a wide neck).
12.
Fill the ketchup into the jars according to canning rules (see below).
13.
The canning time with a canning machine is 30 minutes at 90°C.
14.
Canning preserves the ketchup for about 12 months. Store opened jars in the refrigerator and consume quickly.