Is cooking in a pressure cooker healthy and safe? How it works?

Although the pressure cooker has existed for several centuries, it has only succeeded in being a very common utensil in the last hundred years.
Modern society uses it mainly because of its great advantage: namely the ability of halving the cooking time. But not everyone feels great sympathy for its whistle, some for fear that it may explode and some see it as a contraption capable of spoiling nutrients.
Until this year, not preferring it over the traditional pot was a personal matter of “little importance”; today, abetted by the energy crisis, its use can make a difference in improving household economy (it guarantees less than 40 percent of gas/energy). So let me try to answer some of the most asked questions about a pressure cooker “Is cooking in a pressure cooker healthy and safe?”, “How does a pressure cooker work?”, “Can a pressure cooker explode like a bomb?” or “How much we save by using a pressure cooker?” and more.
 

How do pressure cookers work and how they are able to reduce cooking time

People like me who live at sea level may not know the basic principle; it’s different for those who live high in the mountains: atmospheric pressure palpably affects the boiling point of water and consequently the amount of time you spend cooking.
But how?
If you took chemistry classes in school, you probably remember the Ideal Gas Law or the Perfect Gas Equation:
PV=nRT, where P denotes the pressure, V the volume and T, on the other hand, the temperature (to be fair I specify that “R” is the gas constant and “n” is the number of moles; although in our example we will ignore them since they will not affect our equation).
Indeed we will even ignore the volume, since the pot will have a stable volume throughout the cooking time.
This new equation demonstrates, very simplistically, the strong link between pressure and temperature: higher pressure leads to higher temperature and vice versa.

The pressure cooker works by employing the following physical principle.
The boiling point of water is directly correlated with atmospheric pressure: if it is high, as at sea level (at sea level (0 meters), atmospheric pressure is 1 bar, 14,7 psi or 1013 millibars), water starts boiling at 100°C/212°F; on the contrary, if the pressure is low, as in the high mountains (e.g., at 3000 m (10000 ft approx), atmospheric pressure is 701 millibars or approx 10,11 psi), water starts boiling at about 90°C/194°F: in practice, the water will boil but will be “colder.”

Increasing the cooking temperature is not possible by continuing with cooking (even if you boil water for 1 hour, its temperature will not be above 100°C/212°F): the only way is to increase the pressure.

This can be achieved either by decreasing the altitude, by moving to a seaside location (if you are in the high mountains: those who already live on the coast can only “go under water”); or by using a pressure cooker, definitely the most practical and easiest way.
With the continuous heating caused by the stove, the amount of water vapor accumulated inside the pressure cooker increases and begins to occupy all the space; since it cannot escape thanks to the hermetically sealed lid, the internal pressure increases to a maximum of 0.9 bar for European pressure cookers and to 1 bar (or 15 psi) for American ones (different national standards provide for different characteristics).
In this way it is possible to add about 1 bar to the atmospheric pressure; a fact that increases the boiling point from 100°C/212°F to 121°C/250°F (a nominal value reached only by industrial, or sophisticated domestic appliances): all of which results in the reduction of cooking time, giving an inhabitant of Sestriere (the highest municipality in Italy) the possibility of cooking as if he/she were on the seafront.

Some argue that said “miracle” should be traced to another general rule of chemistry: the Arrhenius equation.
That is, for every 10 degrees Celsius increase in temperature, the reaction rate of various chemical and biological reactions doubles.
Since cooking could also be called a chemical reaction, the speed of the reactions related to the process, just like the steam tension/pressure, will be doubled; result: cooking in half the time if the pot reaches 110°C/230°F, or even in a quarter of the time if it reaches 120°C/248°F.

But among the various co-factors responsible for the “magic,” the most experienced of physical accidents on our skin should be mentioned: steam or water vapor.
Steam and liquids have a greater coefficient of heat transfer than dry air; I don’t know about you, but the worst burns I have experienced from steam escaping from the kettle, rather than from hot air coming from the oven when opening its door, despite the fact that it quietly works at twice the temperature!

And so: thanks to what I have just explained so far, it is possible (minimum) halving the cooking time, have a smaller carbon footprint and save money.
But how much?
 

How much can we save with the pressure cooker? And what do we gain?

To the question of what is gained by using a pressure cooker, we immediately answer time.
Time is money, agreed, however, there are equally important things. Let’s look at them:

– using fossil fuels is against the principles of an eco-friendly approach; consequently, reducing their consumption is already a huge gain;

– being able to halve cooking times will open up the horizons of healthy cooking to you, in itself already an incredible gain in every respect;

– from a strictly economic point of view, I invite you to do with me a rough estimate.
From my direct experience I assure you that with the pressure cooker it takes minimum half time for cooking your truly hard to cook food ingredients: it takes about 15-20 minutes to cook brown rice, instead of the usual 40-50 minutes of the regular pot; for beans 20-25 minutes, instead of 40-60 minutes.
Let’s go by calculation.
An average medium size stove of 1.65-kilowatt consumes 0.10 cubic meters of gas for one hour of use. Let us also estimate that using 2 medium stoves for 2 hours per day, (cooking pasta, rice, legumes, pulses, polenta, cereals, potatoes, vegetables, meats, sauces, vegetable or meat broths, boiled meat or turkey or chicken, soups, preserves, jams, chestnuts etc.), for lunches and dinners of a family of four members, results in an annual consumption of: 2×0.10×2×365= 146 cubic meters of gas.
Let us also assume as an average price for 1 cubic meter of gas 1 euro (currently in Italy the price of gas fluctuates between 0.80 and 1.20 euro); the annual cost will amount to: 1.00×146 = 146.00 euros.
In case we manage to save even half, thanks to the pressure cooker, our savings would be exactly: 73.00 euro!

To those to whom such a figure may seem a trifle I ask a courtesy: if walking down the street you should find 73 euros, please leave it there on the sidewalk; maybe after you will come someone capable of giving it the right value!

And we have not even considered the gigantic indirect savings, resulting from the possibility and willingness to cook for the whole family (the consciousness of saving time and money, will entice you to get in front of the stove); thus avoiding very expensive ready-made or prepackaged meals, or those extra dinners out. I cannot quantify to the penny the total savings, but I am sure it would be simply HUGE!

That said, despite the unquestionable economic benefit, I would like to keep you focused on the other aspects (those already explained and the others which I will explain below) of using pressure cookers, far more important.

But before examining the question “Is cooking in a pressure cooker healthy and safe?” let’s discover if they are really dangerous!

Are pressure cookers dangerous? Can they explode like a bomb?

Before answering, some necessary background.
From the earliest examples of pressure cookers (those of 17th century), much has changed until today.
Current pressure cookers normally have 2 valves, designed to relieve excessive or operating pressure.
The first is a regulating valve, which also acts as a whistle in older models.
The second, located not far from the regulating valve, is screwed onto the lid and contains inside a kind of disc covered with synthetic rubber.
In case the pressure rises above the predetermined safety threshold, the valve is able to detect “danger”, preventing any accidents by melting the rubber: at which point the excess steam escapes freely from the raised disc, without causing damage.
I personally experienced it, due to my own forgetfulness, and I can assure you how perfectly the system works…except for some smearing of the kitchen walls.
After that, I just had to replace the safety valve and ready again to cook quickly our meals.

I mean, with today’s modern and safer models, if they have no manufacturing and design defects, you’d really have to sabotage them to cause an explosion!

To cause the explosion in practice one should do the exact opposite of what is recommended in the instruction booklet, which in fact indicates to:

– never fill the pressure cooker more than the “Max Level” line, usually marked at 2/3 of the pot;

– never use it without a minimum of water inside;

– never use the lid dirty, with the safety valves clogged with the remains of previous cooking;

– never use too much oil;

– use the cooker only after the lid is properly aligned;

– perform periodic inspections of parts such as gaskets and valves, replacing them periodically and/or after any falls or other events that may cause damage;

– ensure vigilant presence in the vicinity throughout the cooking process and put on a timer if necessary;

– do not cook foods composed of small granules, (some manufacturers warn against lentils and spices such as oregano for example) capable of clogging valves;

– do not wash the lid in the dishwasher;

– reading and well understanding the manufacturer’s instructions for use.

More than technical directions, these are actually common-sense rules; therefore, by sticking to the above advice, you can rest assured: a modern pressure cooker WILL NEVER BE DANGEROUS, NOR WILL IT EXPLODE LIKE A BOMB.
 

Is cooking in a pressure cooker healthy?

Finally I will try to examine deeply the most asked question: Is cooking in a pressure cooker healthy?
“Traditionalists” reject the use of the pressure cooker, accusing it of being an unnatural method of cooking food; removing this aspect, they often object to it because of the damage to nutrients, given the very high temperatures.
Let us therefore clarify.
I cannot deny that cooking itself negatively affects food quality, however, it must be said that there are several factors at play, primarily the time of exposure to high temperatures.
Scientific evidence confirms that prolonged cooking time has a more deleterious effect, in terms of nutritional quality: the very traditional long cooking, even if it takes place around the usual 100 degrees, damages elevated amount of vitamins, minerals and biofunctional molecules such as antioxidants.
What’s more, using less water than boiling in a regular pot is a good thing to keep water-soluble nutrients from dissolving in the cooking water.

To cook or not to cook?

In order to lead a healthy existence, the human body must take in a large amount of nutrients found in ingested foods.
I am not just referring to proteins, carbohydrates and fats, but to the whole baggage of functional molecules such as vitamins, minerals, antioxidants and more contained within each bite. Their level is never the same as nominally stated, as a myriad of physical and chemical variations are there to threaten their safety: for example, simple washing, peeling, preserving, freezing, drying and cooking. In each of these steps, the food loses something from its initial nutrient level; but the most important threat comes from the application of heat, as in the case of cooking.
So the right question maybe is not ‘Is cooking in a pressure cooker healthy?’, but should be “Is cooking healthy?”.
Then again, most foods cannot be consumed raw; beyond being disgusting or not, our most frequently consumed food products would be not only indigestible, but even toxic: think of potatoes, legumes, eggplants, beans or meat

If we agree on cooking them, we determine our options.
Among the most commonly used cooking methods I can mention:

– boiling;

– baking;

– microwave cooking;

– steaming;

– oil frying;

– hot air frying;

– stir-frying;

– pressure cooking.

As already explained the higher the temperature, the higher the damage caused; therefore, if we want the healthiest and most natural food possible, let’s start by eliminating high-temperature cooking, such as frying that reaches 180°C/356°F (it does not change whether an air fryer or classic oil frying) and baking, which for some foods can also cheerfully exceed 180°C/356°F).

The new ranking of the remaining cooking methods according to their operating temperature is as follows:

– stir-fry with its 120°C/248°F;

– pressure cooker (maximum 120°C/248°F: actually, most domestic models do not exceed 110°C/230°F);

– boiling, with its 100°C/212°F (maximum);

– microwave: since it cooks using water molecules, it would not reach beyond 100°C/212°F; but since it is not a traditional method at all, we will not consider it in this new list;

– finally, steaming which takes place at a maximum of 100°C/212°F.

Scientific research confirms that steaming and quick sautéing or stir-frying, are the healthiest methods, when it comes to protecting nutrients in our food.
But, there is always a “but”, steaming can be applied yes to almost all foods, especially vegetables, fish, and rice, but not all recipes can be made quickly.

Moreover, we should also consider the basic aspect of a sustainable diet: deliciousness! While food cooked with steam is very healthy, not everyone likes the result.

Conversely, quick stir-frying can increase the level of appreciation; unfortunately, not all foods can be cooked with this method: legumes, meats and most grains require more time and/or water for cooking.

Let’s see also what does science say on the question of “Is cooking in a pressure cooker healthy?”

In a research conducted in 2010, a significant loss of phenolic content, (responsible for antioxidant action) was noted after boiling cauliflower, peas, spinach and chard; in contrast, no reduction in phenolic substance levels for some of the tested vegetables detected (or at most a minor reduction in the same levels) after pressure cooking[1].

Another research from 2015, showed that the best methods for maintaining the nutritional qualities of vegetables (folates, carotenoids and vitamin C) were cooking with steam and with a pressure cooker; in contrast, boiling proved to be the least suitable method for this goal[2].

Still other research, which sought to determine the best cooking method to maintain the beneficial compounds in broccoli (such as vitamin C and sulfurophan), showed that boiling, or even steaming broccoli, causes a greater reduction in these molecules than microwave cooking, or pressure cooking, or the combined use of the two techniques[3].

Hernandez and colleagues confirm that boiling is the most detrimental method for broccoli’s antioxidant and vitamin C levels[4].

More or less the same is also indicated for the cooking of edible mushrooms: pressure cooker and stir fry, are even able to produce great positive effects; unlike boiling, the originator of negative effects[5].

Esther Pauline Rani and colleagues, too, highlighted similar outcome during their experiments for the cooking of the vegetables under study[6].

There is more to be said and of no small importance.

Cooking is much more than just having a food taste good; it serves mainly to make our foods digestible by denaturing peptide bonds, which retain nutrients; and by eliminating molecules defined as anti-nutrients such as pectin, phytic acid, saponins and lectins.

Cooking in the pressure cooker is particularly notable for destroying lectins and phytic acid found in legumes and grains, which cause a potential problem especially for those with a purely plant-based diet[7, 8, 9, 10]. So the question maybe should be “Not cooking food with a pressure cooker can be unhealthy?” instead of “Is cooking in a pressure cooker healthy?”
 

Conclusions

After reading all this data, it is easy to reply to the question of “Is cooking in a pressure cooker healthy?”: it is clear that the pressure cooker proves to be a viable means of cooking food in a healthy, economical and sustainable way.
I can list other advantages of the pressure cooker as following:

– versatile, since you can use it to cook risotto, pasta, or even fruit desserts such as chestnuts or quinces;

– practical, since everyone can use it very easily (there are now models that even allow the setting of cooking times);

– quick: it halves the cooking time;

– safe: by following the easy instructions it is impossible for it to explode;

– not toxic: since it is completely made of stainless steel, it does not cause unhealthy and harmful interactions with your food.

– able to bring you closer to healthy cooking, as all foods once avoided because of long cooking times, such as legumes or whole grains, can finally be prepared quickly;

– a true friend to your pocket and the environment: it will save you money, energy and fossil fuel consumes.

And if you really want to aim to get the most out of your food, it is good to cook vegetables quickly like stir-fry or steam cooking, for a maximum of 5 minutes; but for everything else you should undoubtedly prefer the pressure cooker.

Enjoy your healthy and quick meals and good revolution to all

Bibliography
1) NATELLA, F., BELELLI, F., RAMBERTI, A. and SCACCINI, C. (2010), MICROWAVE AND TRADITIONAL COOKING METHODS: EFFECT OF COOKING ON ANTIOXIDANT CAPACITY AND PHENOLIC COMPOUNDS CONTENT OF SEVEN VEGETABLES. Journal of Food Biochemistry, 34: 796-810
2) Sylvie Bureau, Sonia Mouhoubi, Line Touloumet, Caroline Garcia, Florie Moreau, Valerie Bedouet, Catherine M.G.C. Renard. Are folates, carotenoids and vitamin C affected by cooking? Four domestic procedures are compared on a large diversity of frozen vegetables,
LWT – Food Science and Technology. Volume 64, Issue 2, 2015, Pages 735-741, ISSN 0023-6438
3) Galgano, F., Favati, F., Caruso, M., Pietrafesa, A. and Natella, S. (2007), The Influence of Processing and Preservation on the Retention of Health-Promoting Compounds in Broccoli. Journal of Food Science, 72: S130-S135.
4) Abad Arturo López-Hernández Ana Sofia Ortega-Villarreal Jesús Alberto Vázquez Rodríguez Manuel López-Cabanillas Lomelí Blanca Edelia González-Martíne. Application of different cooking methods to improve nutritional quality of broccoli (Brassica oleracea var. italica) regarding its compounds content with antioxidant activity, International Journal of Gastronomy and Food Science, Volume 28, 2022, 100510, ISSN 1878-450X,
5) Gan CH, Amira N, Asmah R. Antioxidant analysis of different types of edible mushrooms (Agaricus bisporous and Agaricus brasilliensis). International Food Research Journal. 2013; 20(3):1095-1102
6) Esther Pauline Rani, Regi Raymon Sharmelee Fernando. International Journal of Home Science Effect of cooking on total antioxidant activity in selected vegetables 2016; 2(2): 218-222 ISSN: 2395-7476 IJHS 2016; 2(2): 218-222
7) Srivastava, R. P., and Hina Vasishtha. “Dietary fiber, protein and lectin contents of lentils (Lens culinaris) on soaking and cooking.” Current Advances in Agricultural Sciences 5 (2013): 238-241.
8) Srivastava, S. and Khokhar, S. (1996), Effects of Processing on the Reduction of β-ODAP (β-N-Oxalyl-L-2,3-diaminopropionic acid) and Anti-Nutrients of Khesari Dhal, Lathyrus sativus. J. Sci. Food Agric., 71: 50-58.
9) Kataria, Anita, B. M. Chauhan, and Darshan Punia. “Antinutrients and protein digestibility (in vitro) of mungbean as affected by domestic processing and cooking.” Food Chemistry 32.1 (1989): 9-17
10) Ibrahim, S. S., et al. “Effect of soaking, germination, cooking and fermentation on antinutritional factors in cowpeas.” Food/nahrung 46.2 (2002): 92-95

You might also like:

• Tempeh and Red Bell Pepper Stuffed Portobello mushrooms with Potato rösti and Delica squash
• Golden Milk (Turmeric Milk): an Ayurvedic remedy, which tastes divine