While it would be difficult to substitute another vegetable for tomatoes in any form, substituting one type of tomato product for another works for many recipes. All tomato products share a sweet and sour taste combination, a high acidic content and a medium flavor profile, meaning they are stronger than the profile of summer squash but milder than hot peppers. Beyond that, the differences relate more to texture than they do to taste.
Substitutes for Tomato Sauces and Juices
Because tomato juice is basically a liquid tomato sauce with added spices, you can substitute tomato sauce in all recipes that call for juice. To convert tomato sauce to juice, add equal parts of tomato sauce and water in whatever quantities you need. Alterntively, if you need a substitute for tomato sauce, use 3 parts of tomato paste to 4 parts of water. For either sauce or juice, season the final product to taste, using salt and pepper in addition to seasonings such as cumin, cayenne, smoked paprika and Worcestershire sauce, if desired.
Substitutes for Canned Tomatoes
A substitution for canned tomatoes takes a little more time to prepare, but it provides a similar end result in any recipe. Roasting fresh tomatoes dredged in a little olive oil and then placed in a very hot oven until the skins crack -- about 30 minutes -- provides the most intense flavor. Remove the skins when the tomatoes cool. Alternatively, peel fresh tomatoes by submerging them in near-boiling water for a minute or two until the skins crack -- the peels will slip off easily. For each 1-pound can of tomatoes -- either diced or whole -- use about 3 cups of chopped, fresh peeled or roasted tomatoes. Cook the tomatoes on low heat for about 10 minutes or until the mixture achieves the consistency you want. The longer you cook them, the more they will reduce and the thicker they will become.
Substitutes for Fresh Tomatoes
Canned tomatoes and sun-dried tomatoes both approximate the taste of fresh tomatoes in all recipes. Be aware that canned tomatoes are not as firm as fresh, and sun-dried tomatoes are more chewy. Reconstitute dried tomatoes by pouring boiling water over them and letting them soak for about 30 minutes. Use them in many of the ways you would fresh tomatoes. Drain a 14-ounce can of tomatoes to substitute for about 4 or 5 medium fresh tomatoes. For tomato flavor without the tomatoes themselves, use about 1 tablespoon of tomato paste for each medium tomato.
Substitutes for Paste and Ketchup
Tomato sauce can substitute for both tomato paste and ketchup in any way you want to use them. To transform the sauce into a substitute for paste, use twice as much sauce as paste called for in your recipe and reduce other liquids to compensate. To make ketchup from tomato sauce, use the same amount of sauce as you would ketchup and enhance the flavor of the sauce to resemble your favorite ketchup by adding a few tablespoons of vinegar and sugar and a dash of Worcestershire sauce and paprika for each can of sauce.