There's a recipe for homemade ketchup in Mark Bittman's How to Cook Everything that I've been wanting to try. You might consider checking this book out @ your library, because there's loads of recipes for homemade sauces, condiments, and spice mixes. Ketchup, seventeen variations on homemade mustard, mayo, pan sauces, BBQ sauce, salsas, chutneys, you name it.