I've been canning tomatoes for over 30 years, Italian style. I grind the tomatoes after cooking, jar the sauce, and then boil The only ingredients I add, after grinding, are fresh basil leaves and a pinch of salt on the top of each jar. I learned from two Old-World Italians. One of them would re-cook after grinding, but did not boil the filled jars. The other would fill the jars with the ground tomatoes and then boil the jars. In 20 years of using the second method, I've only had to dispose of 3 jars (a bad tomato crop). The first method resulted in more waste. Believe it or not, the "pinch of salt" is a preservative. Adding garlic, onions, or peppers to the sauce before jarring may result in more waste -- more prone to bacteria forming.
I've been canning tomatoes for over 30 years, Italian style. I grind the tomatoes after cooking, jar the sauce, and then boil The only ingredients I add, after grinding, are fresh basil leaves and a pinch of salt on the top of each jar. I learned from two Old-World Italians. One of them would re-cook after grinding, but did not boil the filled jars. The other would fill the jars with the ground tomatoes and then boil the jars. In 20 years of using the second method, I've only had to dispose of 3 jars (a bad tomato crop). The first method resulted in more waste. Believe it or not, the "pinch of salt" is a preservative. Adding garlic, onions, or peppers to the sauce before jarring may result in more waste -- more prone to bacteria forming.