As we're making a large batch of ketchup, you'll need to blend and add your ingredients into the slow cooker a little at a time.
Add the peppers and onions to the blender.
Then add the tomatoes a little at a time.
Add a handful of basil to the blender with some of your tomatoes.
Add a tablespoon of coriander seeds (adjust for yourself if you're not a fan of coriander, then add a little less).
Then add the peppercorns (it adds a really nice flavour).
Add the oil and fennel (again, adjust to your taste). You may want to chop the fennel up to help with the blending process.
Again, add the blended mix to the slow cooker as you go.
Next to go in the blender are the celery sticks and garlic. I'm a big fan of garlic, and I will be using eight garlic cloves. Reduce it if you prefer a little less, but remember that some of the garlic taste will go away when you're cooking it, so it won't be as strong as it might appear initially.
Add your brown sugar straight into the slow cooker. I tend not to use sugar too much; I use alternatives, so I use erythritol but use what you like.
Add the remainder of your tomatoes to the blender.
Peel and chop the ginger into smaller pieces to make it easier to blend and add to the blender.
Now add the red wine vinegar.
Mix all of the blended ingredients inside the crockpot and add a litre of water.
Switch the slow cooker to high and cook for an hour.
Then remove the lid and cook on low until the ketchup thickens to a consistency you like. I left mine for 12 hours to reduce.
If the liquid separates, you can use an immersion blender and blend the sauce before you run it through a sieve.
Be sure to let the mix cool slightly before blending. And blend to your preferred consistency. You can add xanthan gum if you want to.