Because chiles are naturally low in acid, canning them requires special precautions that differ from those followed when canning high-acid fruits. Growth of micro-organisms particularly must be avoided.
Some bacteria cause food spoilage, while others produce toxins that cause illness or death.
For example, Clostridium botulinum is a harmless bacteria in air. In little or no acid, an air-free canning jar, and temperatures between 40degF and 120degF, this bacteria grows and produces a deadly toxin that can cause serious damage to the central nervous system or death when eaten in even minute amounts. Pressure processing is the only safe way to can chiles and other non-acid foods. Boiling water produces steam. Steam under pressure raises the temperature much higher than it normally would be without pressure.