what exactly is the right proportion of tomatoes/tatashe/pepper to use for stew to make it taste best? also what is the best type of tomatoes for stew? is the oblong smaller ones or the roundish tomatoes?, cheers

Getting Tomatoes to taste pleasant is about technique not proportion.
How? Weather fresh or tin, fry tomatoes in plenty of oil, stir frequently till it begins to stick to the bottom of the pot. This kills that sour taste of tomatoes in stew. In fact you can also mix tomatoes with melon or vegetable soup too.

@Op
my small contribution


squeeze out the tomatoes juice and wash out the seeds before grinding
that certainly will take out the sour taste
i also take out the seeds of the big red peppers too( don't know why,sort of inherited that way)