Would this be safe to do?
I have 3 pts of tomato puree that I canned in 2011. I plan to make ketchup this fall/winter, using a recipe that calls for 7qts to start with, spices, vinegar and all cooking down to 4 pts. I've been making this recipe for almost 45 years, and recently have taken to freezing the puree to make the ketchup in winter when things have slowed down--and I don't mind running the stove for many, many hours. But I've never used canned puree for this recipe. So my question: will it be safe to use those 3 pts mixed with frozen puree that I have yet to make.