Electric pressure cookers have evolved substantially since the first patent was filed on January 9th, 1991. Based on the cooking control capability, we can classify electric pressure cookers into three generations.
1st Generation: Mechanical Timer
The 1st Generation electric pressure cookers already have the essential pressure and temperature sensors. Both sensors act as a threshold moderator. When either the threshold of pressure or that of temperature is reached, the power to the heating element is cut. The only user-accessible control is via the mechanical cooking time controller. This mechanical controller offers estimated control on cooking duration. There is no delayed cooking capability.
Basic safety mechanisms, such as locking the lid under pressure and excess pressure protection, have been implemented in the 1st Generation cookers.
1st generation electric pressure cookers are seldom seen in North America. However, in Asia, they are still very popular with cost-conscience consumers.
2nd Generation: Digital Controller
The 2nd Generation electric pressure cooker builds on top of the capability of the 1st generation with a digital controller. Delayed cooking becomes possible. Pressure sensor is also electronically connected to the controller, so that a count-down timer can be shown when working pressure is reached.
Safety is also improved with additional sensors. Most notably, if the lid is not fully locked, pressure cooking would not start. This avoids the potential risk of blowing up the lid under pressure cooking.
Many of the electric pressure cookers sold in the North America today are still 2nd generation.
3rd Generation: Smart Programming
With the advance in pressure and temperature sensor accuracy, the 3rd Generation electric pressure cookers implement sophisticate control with digital technology. Two most remarkable features are Smart Programming and Enhanced Safety. These features greatly improve cooking result, maintain consistence and enhance safety.
Each 3rd Generation cooker is fitted with a microprocessor. With the accurate readings from pressure and temperature sensors, the microprocessor can be programmed to perform complex cooking tasks. The Smart Programs are tailor made for specific cooking purpose by varying heating intensity, temperature, pressure and cooking duration, to achieve optimized cooking result and maintain consistence. A typical example is in multigrain cooking program where the grains are soaked at ~60C/86F for a period to soften the grains before cooking starts. Please see our Smart Programming article for more details.
With the microprocessor programs, more sophisticated safety mechanisms become possible. For instance, one common mistake is misplacing the stream release at the open position while starting cooking. With the steam release open, pressure never builds up in the cooking pot. Earlier generation cookers would continue heating. If the situation is not corrected on time, all liquid in the cooking pot would evaporate and the food would be spoiled. The 3rd Generation cooker implements a mechanism called, Leaky Lid Protection, where the microprocessor detects the excess long pre-heating period and stops the heating with an alarm. More on the safety features here.
All Instant Pot models are 3rd Generation electric pressure cookers.