I have an old recipe for Green Tomato/Ginger Jam , it needs 3/4 tsp tartaric acid, can I substitute cream of tartar and if so how much?
Green Tomato/Ginger Jam: Skin 1 3/4 lbs green tomatoes by plunging them into boiling water for 8-12 minutes. Cut the tomatoes into quarters, sprinkle with 3/4 lb sugar, 1 1/2 tsp,powdered ginger and 3/4 tsp tartaric acid. Leave to stand over night. Next day, add 2 oz root ginger and 3/4 tsp lemon essence. Place in a pan and simmer until tender. Add a little extra water if the tomatoes are very hard. Add another 1 3/4 lbs. of sugar. Stir until dissolved and boil in an open pan for about 5 minutes.
Green Tomato Pickles: Slice 3 lbs green tomatoes into a pan with 1 lb onions, sliced, 1 tablespoon salt and 3/4 pt vinegar. Cook about 45 minutes. Add 8 oz brown sugar, 1 tsp ground ginger, 1 tsp dry mustard and 1/2 tsp cayenne pepper, and cook slowly for 1 hour, stirring constantly. Bottle while hot and then seal immediately.