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The Science of Pressure Cooker

The Science of Pressure Cooker

It's one of the most common kitchen tools, but are you sure you know how a pressure cooker actually works? Here are some basic principles and tricks.

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Have you ever boiled a piece of meat at 5800 metres below sea level? I doubt it. And yet, that is practically what you do every time you use a pressure cooker since the same, identical conditions are recreated inside this type of cooking utensil.

However, to understand how a pressure cooker works, you need to grasp the role played by physics in this particular cooking method.

Incidentally, for once, we are in possession of some precise information regarding its origin: it first appeared in 1679, under the name of Papin’s Digester, in honour of its inventor, French physician Denis Papin. Who, starting from this invention, also came up with a steam engine.

How does a pressure cooker work?

The working of a pressure cooker is based on a very simple principle: water boils at 100°C, but only at sea level and therefore at a pressure of approximately 1 Atmosphere.

If the pressure is any lower, as it is for instance at high mountain altitudes, water will boil at a lower temperature, as mountaineers know perfectly well, since they can enjoy pasta cooked in water at a temperature of just 90°C.

Vice versa, if the pressure rises, as a result of our pan being taken to the ocean bed, a higher temperature is needed to boil water. This depends on what is known as “vapour pressure”: in other words, based on the amount of pressure, water molecules need more or less energy to “escape” and trigger the boiling process.

How to use a pressure cooker

On the grounds of this principle, the pressure cooker raises the pressure of the water vapour formed by heating the moisture it contains, to a point that is higher than the external pressure. However, to prevent it from exploding, at a given point, a valve “releases” the excess vapour: this creates a point of “equilibrium”.

What does this actually mean? That the liquid generates sufficient steam to keep the pressure constant. This is all expressed in a formula, known as the “Ideal Gas Law”: pV = nRT. The law whereby pressure, volume and temperature are always perfectly balanced, even though there are obviously other laws to bear in mind.

If we set scientific reasoning aside for a moment and return to our beloved kitchen hob, the salient fact is that the pressure inside this type of saucepan is as high as 2 ATM, which enables water to boil at 120°C or more. This is why any food will cook much faster with this method.

pressure cooker pork ribs to try at home

Having duly covered the scientific aspects, we shall now take a look at a recipe you would never have dreamed of preparing in a pressure cooker, but which effectively demonstrates the versatility of this utensil. What do pork ribs bring to mind? Perfect for barbecues or, at the most, for oven roasting.

Get yourself one and a half kilo of ribs, together with an onion, a glass of red wine, 750 grams of top quality puréed tomatoes (make sure they don’t taste in any way acidic!), extra virgin olive oil and salt. Then you need a marinade of wine and sage with which to cover the ribs for one night in the fridge, after having removed any excess fat.

At this point, dry the ribs very thoroughly. Put a generous quantity of olive oil in the open pressure cooker and gently fry the finely sliced onion in it. When soft, add the ribs and brown them well. Pour in the wine, give everything a stir and allow the wine to evaporate before seasoning with a little salt and pepper.

Now, add the puréed tomatoes and a glass of lukewarm water. Close the pressure cooker and let it cook for 30 minutes until you hear the hiss of escaping steam. Finally, let the pan release the steam and serve the ribs nice and hot with their excellent sauce, accompanied with soft polenta.

Now, please let us know if these are not the tastiest and most tender pork ribs you have ever eaten. And don’t forget to propose a toast in honour of Papin!

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