The Complete Handbook of Pressure Cookers & Canners

Chapter 1: Understanding Pressure Cookers & Canners

Pressure cookers and canners work by using steam pressure to raise the boiling point of water beyond its normal 100°C (212°F) at sea level. At higher pressures, water boils at higher temperatures, which means food cooks faster and reaches temperatures sufficient to kill heat-resistant pathogens like Clostridium botulinum, the bacterium responsible for botulism. Understanding this basic principle is essential because it explains why pressure-based cooking is not simply a faster version of boiling or steaming—it fundamentally changes what is chemically and microbiologically possible in a sealed container.

The sealed vessel is the core design feature. A pressure cooker or canner is a pot with a locking lid that contains steam pressure inside. The lid has gaskets (seals), safety vents or valves, and a pressure indicator—either a weight-based valve or a dial gauge. As the liquid inside heats, it converts to steam. Because the vessel is sealed, this steam cannot escape, so pressure builds. The safety valve prevents pressure from exceeding the cooker's design limit by releasing excess steam. The result is a high-temperature, high-pressure environment that cooks food or preserves it in ways that are impossible in an open pot.

Why does this matter? Standard boiling at 100°C denatures proteins and softens vegetables, but it does not kill all bacterial spores. The bacterium Clostridium botulinum produces spores that survive boiling and can germinate in low-acid, anaerobic (oxygen-free) foods stored without refrigeration—a risk that has killed people. Pressure cooking raises the temperature to