Wipe tomatoes clean, nip off base scar. Chop onion, tomatoes roughly. Crush garlic, ginger and mix with tomatoes and onions. Put in a large, heavy pan, drop in spice pouch. Heat while stirring frequently. Do not allow to burn at the bottom. When the tomatoes are very soft, take off fire. Remove pouch, blend smooth, sieve to remove skins, seeds, etc. Add chilli powder,salt and sugar. Boil till consistency achieve plate test. Add vinegar, boil for 5 minutes. Remove from stove, add sodium benzoate immediately. Stir and fill in sterilized bottles while still hot. Cap immediately.