The Ingenious Design Behind a Humble Kitchenware Appliance – The Pressure Cooker

Kitchen appliances are the heart and soul of our Indian kitchens. They are the true partners of our beloved chefs and cooks, and the way they operate decides how delicious our food turns out to be. What makes these kitchen appliances special in the way they cook food is the design behind them. One such kitchen appliance with an ingenious design is the ‘Pressure Cooker.’

The prototype of the modern-day pressure cooker was the steam digester invented in the 17th century by the physicist Denis Papin. It was a revolutionary design for that time period. The pressure cooker works on the simple principle of expelling air from the vessel and trapping the steam produced from the boiling liquid. However, what’s fascinating about the humble cooker is its design that allows the steam to emerge.

To design any kitchen appliance, Product Designers have to ensure three important factors: Effectiveness, Safety, and Cheap. For pressure cookers, the safety takes a higher slab of importance. That’s because of its unique working mechanism. If the air trapped inside the vessel doesn’t get a chance to escape, the pressure cooker might explode due to the intense pressure buildup.

A pressure cooker acts as a sealed vessel. Here, when you heat water, and enough water turns into vapor, the water vapor gets sealed inside the cooker. The increased air pressure also prevents the remaining water from becoming water vapor. This way, we can ensure that the required gravy remains inside the cooker and we get our preferred recipe.

What effectively happens is that the boiling point of water increases. Hence, inside a pressure cooker, water doesn’t boil at 100* celsius. It rises to 121* celsius. This brings us to the biggest advantage that a pressure cooker provides – faster cooking of food, and with less energy. This is what makes the device so brilliant, and why the majority of Indian households have adopted it so easily. It saves time in a hectic Indian household, reduces the chaos around the kitchen, and makes food preparation much easier. But the execution of it isn’t that simple.

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However, we are missing a poignant detail that is imperative for a pressure cooker to function this effectively. What happens to the pressure that builds up in the form of intense vapor? It needs to be released. If not, as mentioned above, the pressure cooker could effectively turn into an explosive bomb.

Therefore, engineers and designers came up with an inventive solution. A pressure cooker has a metal weight that sits on top of the valve attached to the body. The metal weight is weighed, measured, and designed to the exact precision in which it will work. When placed lightly above the valve, the divots match and create an interlocking pattern. But the weight and mechanism are such that enough pressure from the vapor inside can lift the metal weight and release the air.

Once released, the metal item comes back down and creates the interlock again. This is what we colloquially call “Seeti” in Hindi. In Indian households, we have often heard our mothers ask us to count the number of ‘Seetis’ in a pressure cooker. That’s because our mothers had estimated how many times the air pressure needed to be released before the item inside is completely cooked.

A ‘Seeti’ is nothing but the sound made by the pressure cooker when air is released at high pressure and speed. This is the ingenious design behind the pressure cooker that utilizes the scientific concept of ‘Gravity’ to make it fully effective. It is gravity that brings the elevated metal weight down and into the valve again. The process continues until we allow it to.

The Additional Problems Indian Households Faced with Pressure Cookers

India experiences a wide variety of climatic and geographical diversity. While some parts experience rainy weather for most of the year, some have extremely cold weather. A large part of India, though, experiences a tropical climate. Overall, India is still a hot and humid country. This created an issue for the pressure cookers.

In hot weather, the valves and the metal weight often get too sticky and dirty. When the air pressure releases from the valve, it isn’t just the vapor that escapes, but tiny, dense, liquid particles from the dish that’s being cooked inside as well. Over time, this accumulation creates a sludge-like substance on the valve and, therefore, on the metal weight. The hot and humid weather of India further enhances this accumulation and makes the valve and the metal weight very sticky.

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To combat this sticky problem (pun intended), engineers and designers came up with a Plan B. They created an additional safety valve just right beside where the metal weight sits. If and when the air pressure reaches 1.5 bars, and the metal lid refuses to rise due to the sticky grease around it, the secondary safety valve takes charge and acts as the releaser of gas. This, once again, saves the pressure cooker from blasting. The safety valve is made from a special alloy that melts at that precise temperature when the air is ready to rise and escape. Once melted, the job of the safety valve is done.

However, this is not a naturally reversible process. Once it happens, the customer needs to take it to the service center and get it replaced with a new one. Remember, the metal lid and the valve are still the primary mode of gas removal from the cooker. The safety valve is only required when the metal lid fails to lift. But even the safety valve wasn’t enough as a sure-shot, risk-free solution.

The alloy of the safety valve might melt, but one could still be left with dirt and grease accumulated around that opening. That grease could potentially fill that gap and solidify over time. This, once again, poses a problem for the pressure cooker to release gas.

A Third Solution for Pressure Cookers in India

Meet TT Jagannathan, a gold medalist from IIT Chennai and a PhD holder in Operations Research from Cornell University. He is the president of the TTK Group, a conglomerate with its presence across several industry segments such as consumer durables, pharmaceuticals, supplements, etc.

Mr. Jagannathan, who recently passed away, pioneered a 3rd safety system. This time, it was an almost 100% safe safety system. Far away from the top surface of the pressure cooker, where both the metal lid and the safety valve lay, Mr. Jagannathan created another small hole for the pressure to release. It lies on the lower ridge of the pressure cooker lid. He also added another slightly-longish slit near the hole. Both these openings acted as the release of gas in case the first two openings failed.

When the pressure increases beyond a certain safety point, and both the safety valves have failed, the pressure inside the cooker will push the gas release through the slit and the hole. This will allow excess gas to escape through the smaller holes. Mr. TT Jagannathan made this design for Prestige Cookers, and that’s why they are one of the leaders in this industry.

A humble kitchen appliance like a pressure cooker teaches us so much about product design. It is a notable example of what small design changes can do to enhance and ease our lives. While the aesthetics remain the same, the efficiency goes up a few notches above.

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