Thicken tomato sauce without using tomato paste by cooking the sauce uncovered,on a low heat for several hours. This method is called reducing and produces a thick, more flavorful sauce. Start with double the amount of sauce that you wish to end up with.Continue Reading
Place the thin sauce into a large saucepan. Add 1 tablespoon olive oil to help reduce boil over.
Cook the sauce on medium high heat, bringing it to a boil.
Lower the heat to the lowest setting allowing it to continue to bubble at a slow rate. Make sure sauce is boiling slowly. This helps the liquid to vaporize. Keep the saucepan uncovered, allowing the steam to escape.
Continue to cook the sauce on a low heat for several hours, stirring occasionally to avoid sticking. The liquid in the sauce boils slowly away leaving more solid matter. This creates a thicker, more flavorful sauce.