Step 1: Prepare your canning equipment. Wash jars, lids, and bands in hot soapy water. Sterilize jars by placing them in boiling water for at least 10 minutes. Keep jars hot in the canner or a warm oven until ready to fill. Set new lids aside; they do not need to be boiled in advance, just kept warm according to manufacturer instructions. Bands can be set aside.
Step 2: Prepare the tomatoes. Wash and core the ripe Roma tomatoes. You can choose to peel them, but it’s optional. To peel, blanch them briefly in boiling water (about 30-60 seconds), then plunge into ice water. The skins should slip off easily. Chop the peeled (or unpeeled) tomatoes into approximately 1/2-inch pieces. Place chopped tomatoes in a large bowl.
Step 3: Prepare other vegetables. Finely chop the onions, jalapeños (removing seeds and membranes for milder heat, or leaving some for more spice), and bell peppers. The size of your dice will determine the texture of your finished salsa. For a smoother salsa, you can process them briefly in a food processor, but be careful not to over-process into a purée.
Step 4: Combine ingredients. In a large, heavy-bottomed stockpot, combine the chopped tomatoes, onions, jalapeños, and bell peppers. Add the apple cider vinegar, sugar (if using), pickling salt, ground cumin, and black pepper. Stir everything together thoroughly.
Step 5: Simmer the salsa. Bring the mixture to a boil over medium-high heat, stirring frequently. Once boiling, reduce the heat to a simmer and cook for 20-30 minutes, or until the salsa reaches your desired consistency. Stir occasionally to prevent sticking. The salsa will thicken as it cooks and some of the liquid evaporates.
Step 6: Add fresh cilantro (optional). If you're using fresh cilantro, stir it into the salsa during the last 5 minutes of simmering. This preserves its vibrant flavor and color.
Step 7: Fill hot jars. Carefully ladle the hot salsa into the hot, sterilized canning jars, leaving 1/2-inch headspace. Before filling, add 1 tablespoon of bottled lemon juice to each pint jar (or 2 tablespoons per quart jar). Use a canning funnel to keep jar rims clean.
Step 8: Remove air bubbles. Use a non-metallic spatula or a bubble remover tool to release any trapped air bubbles in the jars. Gently slide it down the sides of the jar. Adjust headspace if necessary by adding more salsa.
Step 9: Clean rims and seal. Wipe the rims of the jars clean with a damp paper towel. Center a hot lid on each jar, then screw on the bands finger-tight. Do not overtighten.
Step 10: Process in a water bath canner. Place the filled jars onto the rack in your water bath canner. Ensure there is at least 1 inch of water covering the tops of the jars. Bring the water to a rolling boil. Once boiling, process pint jars for 15 minutes (20 minutes for quarts). Adjust processing time for your altitude if necessary.
Step 11: Cool and check seals. Turn off the heat and let the jars sit in the canner for 5 minutes before carefully removing them with a jar lifter. Place the hot jars on a wire rack or thick towel on your counter, ensuring they are not touching each other, and allow them to cool undisturbed for 12-24 hours. After cooling, check seals by pressing the center of each lid; if it doesn't flex, it's sealed. If any jar did not seal, refrigerate it and consume within a few weeks, or reprocess with a new lid.