Canning food is an excellent way to preserve the harvest of summer for months to come. Foods are categorized as either "acid" or "low acid" foods depending on their pH level. Pressure canning must be used for "low acid" foods due to the risk of Clostridium botulinum growth. When pressure canning, it is important to vent the pressure canner for 10 minutes before pressurizing to remove air from the canner and ensure a pure steam environment for the required processing times.