Utah State University Extension says you should never use your own recipe when it comes to canning salsa. Because salsa contains acid and low-acid ingredients, the necessary canning process used is decided by the recipe. Whether you use a boiling water canner or a pressure canner is determined by the ingredients of the salsa and how it’s made. So the experts recommend using a tested recipe like from the USDA or National Center for Home Food Preservation (NCHFP).
Per the USDA and NCHFP guide for canning tomato products, it’s important to strictly follow the tested recipes, which can also be found in the guide. Changing the number of tomatoes, onions, or peppers in the recipe could make the salsa unsafe to eat. It’s important to have the right balance of acid (tomatoes) and low-acid (onions and peppers) ingredients. It is ok to change the amount of spice and to switch out bottled lemon juice for vinegar. But those are the only safe substitutions. So next time you want to preserve your extra tomatoes by canning some salsa, remember to pick a trusted recipe.