Thought I would share my experience of making ketchup.
First time I made it, I got loads of tomatoes, chopped them and boiled them up and spent ages passing them through a sieve to get a nice tomato liquid with loads of flavour.
This costs quite a bit, and is a right pain. So after that first attempt, I have used passata (sieved tomatoes) that you can buy easily and saves you all that work.
What you need:
A few packets of passata
Sugar
Spiced vinegar or any tasty vinegar apart from balsamic
Spices
Put the passata into a large pan.
Add about 1oz of sugar (light brown is good) for every lb of passata.
Add around 25ml of the vinegar for each pond of passata.
Add some spices if not using spiced vinegar: White pepper, garlic, cayenne, salt and paprika, all powdered.
Stir, heat and reduce for a while.
The ketchup is ready about 5 min after it has reduced enough to start bubbling blobs out of the pan.
You can vary the amounts of vinegar and sugar, and the spices to suit your taste.
Bottle in empty, clean, sterilised old ketchup or similar bottles.
Keeps fine in the cupboard for at least 6 months, but I would put it in the fridge to be safe.
It is far tastier than Heinz ketchup, and costs slightly less.
Made it loads of times, and it is very popular at barbeques etc.
If you want to make spiced vinegar, get a bottle of normal malt vinegar, add whole spices to it, and leave for 6 months or so. I would put in a stick of cinnimon, a clove of garlic, some peppercorns, some allspice, some star anise etc.