Utah State University Extension
Most tomato-based salsa recipes mix low-acid foods, such as onions, sweet and/or hot peppers, with acid foods, such as tomatoes. USU Extension only recommends research-tested salsa recipes that provide evidence of safe acidification to inhibit Clostridium botulinum growth
Nummer, Brian, "Canning Salsa in a Boiling Water Canner, Generic Recipe" (2008). All Current Publications. Paper 1103.