Most salsa recipes are a mixture of low - acid foods, such as onions and peppers, with acid foods, such as tomatoes. Always use tested salsa recipes to ensure they contain enough acid to be processed safely in a boiling water canner.
Use only high quality tomatoes for canning salsa. Do not use tomatoes from dead or frost - killed vines.
Use only high quality peppers. Do not increase the total amount of peppers in any recipe. However, you may substitute one type of pepper for another. Bell peppers may be substituted for long green chiles. Wear plastic or rubber gloves while handling hot chiles.
The acid ingredients used in salsa help preserve it. You must add acid to canned salsa because the natural acidity may not be high enough. Commonly used acids in salsa are vinegar and lemon juice. Lemon juice is more acidic than vinegar, but has less effect on flavor. Use only vinegar that is at least 5% acid and use only bottled lemon juice.
Spices add flavoring to salsa so the amounts of spices and herbs may be altered in recipes. Do not can salsa that does not follow research tested recipes. They may be frozen or stored in the refrigerator for a few days.
Do not thicken salsa with flour or cornstarch before canning. After you open a jar to use, pour off some liquid or thicken with cornstarch.
Play it safe. Only can salsa from tested recipes to ensure they contain enough acid to be processed safely in a boiling water canner.