Preparation: Start by preparing all the vegetables. Wash and peel the tomatoes, then dice them into small pieces. Finely chop the onions, bell peppers, jalapenos, and cilantro. Mince the garlic.
Cooking the Salsa: In a large stockpot, combine the diced tomatoes, onions, bell peppers, jalapenos, cilantro, and garlic. Stir in the white vinegar, sugar, salt, cumin, chili powder, and black pepper.
Simmering: Bring the mixture to a boil over medium-high heat, then reduce the heat and let it simmer uncovered for about 30-35 minutes. Stir occasionally to prevent sticking.
Sterilizing Jars: While the salsa simmers, sterilize the canning jars and lids in a large pot of boiling water. Let them simmer for at least 10 minutes to ensure proper sanitation.
Filling the Jars: Using a canning funnel, carefully ladle the hot salsa into the sterilized jars, leaving about 1/2 inch of headspace at the top.
Sealing the Jars: Wipe the jar rims to remove any spills, place the lids on top, and secure them with bands. Not too tight - just firm enough.
Canning Process: Submerge the filled jars back into the pot of boiling water using a jar lifter. Ensure the water covers the jars by about an inch. Let them process for 15 minutes to seal the jars effectively.
Cooling and Storage: Carefully remove the jars from the water and let them cool on a kitchen towel. As they cool, you'll hear a "ping" sound indicating successful sealing. Store the cooled salsa jars in a cool, dark place, and they'll stay fresh for up to a year.