Pressure cooking is only a few hundred years old, and it only really became popular for home use in the last century. When I was a child, using first-generation pressure cookers was still considered a bit dangerous. They didn’t have all the built-in safety mechanisms of modern pressure cookers. I’ll never forget how I first learned about pressure cookers. I was eight, and I saw one explode. Spaghetti sauce on the ceiling! On the cabinets!
Those ceiling stains never really went away. They had to be painted over many years later.
As an adult, I didn’t give pressure cooking much thought one way or the other. From traditional foodies I’d heard that pressure cooking is not healthy. “It’s hard on nutrients,” they say. “It cooks at really high temperatures when humans historically cook foods slowly over fire.” Because I’ll almost always stand by the wisdom of my ancestors when it comes to food, this argument made a lot of sense.
But then I started hearing from more and more traditional foodies who use pressure cookers to make excellent, gelatinous broth in a quarter the cooking time. Why did their broth always turn so gelatinous when mine was so hit or miss? If pressure cooking is so hard on nutrients, how can it make such perfect broth with the tell-tale presence of perfect gelatin?
How Pressure Cooking Works
Almost all foods contain water, be they meat, veggies, or fruit. When we cook food, we’re essentially transferring heat from our heat source through the food. As the food heats up, a variety of molecular changes happen, ultimately resulting in cooked food. The primary changes have to do with the heating and transferring of water molecules.
The single greatest limiting factor on how long it takes to cook food is the boiling point of water.
Folks who live at high altitudes know this first hand. Their air pressure is lower, and so their water boils at lower temperatures. (In the mile-high city of Denver, for example, water boils at 204F, and in the camps on Mount Everest water boils at 160F. For those of us at sea level, it boils at 212F.)
Cooking at these lower air pressures affects cook times for many foods since water will begin evaporating sooner and drying out the food more quickly.
Translation? In a low-pressure environment, cooking times on moist foods must be increased. Turning up the heat will not help cook food faster! That’s because the temperature of water will never exceed it’s own boiling point — any higher temperatures and all you’ve got is steam.
Theoretically, if you were at a high enough altitude, you could boil water at room temperature. Boiling, therefore, isn’t really a product of temperature at all, but of pressure!
By increasing pressure, you raise the boiling point of water.
Just as cooking times are lengthened by cooking at the lower air pressure of higher altitudes, cooking times are decreased by cooking at the higher air pressure created by a pressure cooker. That’s why you can pressure cook chicken broth in an hour or two instead of eight or twelve. It’s also why you can pressure cook grass-fed pot roasts in just an hour as opposed to cooking them in your oven for four.
Because the boiling point of the water inside a pressure cooker is elevated, you can cook the food at a slightly higher temperature and avoid water loss. In cooking, liquid loss equals over-cooking, drying out, or burning your food. By avoiding water loss while maintaining higher temperatures, your food cooks more quickly.
What are those slightly higher temperatures? Most pressure cookers will raise the boiling point of water inside them to around 225-235F. This is lower than the lowest setting on Crock Pots, which is usually 250F. It’s also only a 13-23 degree difference from the boiling point of water at sea level — the same difference found between the boiling point of water in Miami and La Paz.
Traditionally, before the invention of modern pressure cookers (which are essentially pots with really well-sealed lids), cooks used to try to accomplish this faster cooking time by weighing down the lids of their pots with stones. This prompted one French inventor to created the first mechanically sealed lid for a pot in 1679 (the lid was screwed in place and weighed down with weights). Pressure cooking was born.
Is Pressure Cooking Healthy?
The biggest argument against pressure cooking by those who think it’s unhealthy is that pressure cooking must be bad for the nutrients in the food because you’re cooking them at higher temperatures and higher pressures.
It’s like saying the cooking method is dangerous, well just because! For reasons!
It’s like arguing that food cooked in Miami (where the boiling point of water is 212F) is somehow less nutritious than food cooked in an Andean or Himalayan village (where the boiling point of water is 190F) just because the air pressure and boiling point are higher in Miami.
Did you know that in numerous studies, pressure cooking has been found to preserve the nutrients in food better than any other method?
In this study, pressure cooking was shown to be the best method for preserving the ascorbic acid and beta-carotene in spinach and amaranth. And in a March 2007 study published in the The Journal of Food Science pressure cooking broccoli preserved 90% of its vitamin C compared to steaming (78%) and boiling (66%).
“But how is that possible?” you ask. “Doesn’t the higher temperature destroy the nutrients?”
Pressure cooking preserves nutrients by reducing cook times.
It turns out that higher cooking temperatures don’t destroy any more nutrients than lower cooking temperatures. If a temperature is high enough to start destroying heat-sensitive nutrients, then those heat-sensitive nutrients will be lost regardless of whether the cooking temperature is 119F or 350F.
It’s not the temperature that matters, but the cooking time!
By cooking foods for shorter lengths of time, pressure cookers preserve the nutrients better, despite cooking at higher temperatures.
Pressure cooking preserves nutrients by using less water.
Why do health and nutrition experts always tell you to give preference to steaming vegetables over boiling them?
Because the nutrients leach out of the vegetable and into the water, and then we dump the water out when serving the veggies!
Pressure cooking uses very little water compared to many other cooking methods, essentially acting like a steam cooker where the steam is not allowed to escape easily (thereby building the air pressure). Less water comes into contact with your food to leach away vitamins and minerals.
And if you do as recommended and let your pressure cooker cool naturally before removing the lid so that the steam condenses back into the small amount of liquid in the pot, you can consume all the liquid with your meal and limit the loss of nutrients to water even further.
Pressure cooking makes grains and legumes more digestible by reducing phytic acid and lectins.
Yep, you read that right. The great enemies found in grains, seeds, and legumes are reduced far more by pressure cooking than by boiling.
In this study done on peas, the phytic acid content of peas soaked overnight and then boiled was only reduced by 29%. But in peas that had been soaked overnight and pressure cooked, the phytic acid was reduced by 54%!
Phytic acid binds minerals and other important nutrients in our digestive tract, keeping us from using them. By reducing the phytic acid content of grains and legumes, we increase their nutrient-availability and render them more digestible.
Pressure cooking is also on par with fermentation as the best way to reduce the lectins (yet another anti-nutrient) in grains.
Turns out, pressure cooking may be the best possible way to cook your soaked beans and grains!
What about acrylamides and other carcinogens?
Yes, high-temperature cooking of some foods, like potatoes, does cause the formation of carcinogenic compounds like acrylomides. But those same compounds will not form in a pressure cooker! That’s because of all the steam trapped in the cooker. Those compounds mostly form in dry cooking methods like roasting or grilling, or in an ultra high-temperature environment like deep frying.
Swiss researchers wanted to test this and found that potatoes cooked at high pressure for 20 minutes had almost no acrylamide formation when compared to other high-temperature cooking methods. (And since a potato will be done after about 10 minutes at high pressure, this was definitely overkill!)
But, doesn’t pressure cooking still denature proteins in the food?
Yes. And so does every other cooking method out there! That is, in fact, one of the primary things that cooking is intended to do. It begins the process of breaking down the proteins in the food, making the food easier for us to digest and assimilate. “Denaturing” the proteins is what causes tough stew meat to become tender when cooked. You want denatured proteins. That’s why you cook your food.
In fact, pressure-cooking arguably increases the digestibility of protein, as shown in this study that found that pressure-cooking soaked peas brought their protein digestibility up to 84%, compared to 81% for those peas that were just soaked and boiled normally. (Interestingly, it drops all the way down to just 74% when the peas are unsoaked and then boiled. YAY soaking!)
And, it’s not just peas. Many studies have been done on how pressure-cooking increases the digestibility of proteins, including this one done with mung beans and this one done with rice. It’s even been shown to make meat more tender than boiling does (and more tender meat is demonstrably easier for our bodies to digest).
So, is pressure cooking healthy?
What do you think? For me, it’s a resounding yes.
It may not be ideal for all things. Vegetables, for example, easily turn to mush in pressure cookers if you’re not super exact and attentive about timing.
But it can dramatically reduce cooking times and increase the digestibility of legumes and grains, so I’ve got no problems with that. I even found a recipe for pressure cooker risotto I’m dying to try. (I really dislike the constant stirring necessary for the “real” stuff.)
And, it can be an excellent choice for last-minute meals. If I miss putting my roast or roundsteak into my crockpot at mid-morning, I can easily begin pressure cooking that same meal later in the afternoon and still have a “fast” dinner on the table that didn’t require us eating out (or eating scrambled eggs!) because of my poor planning.
What about the argument that it’s unnatural or not traditional?
Maybe I’ve convinced you that pressure cooking can be healthy. But you still hesitate because it’s not been a historically embraced method of cooking. Creating a pressure difference like this is unnatural, you say.
Here’s the deal. The difference in the boiling point of water in a pressure cooker vs. Miami (sea level) is the exact same difference found between Miami and La Paz. That translates into WIDELY DIFFERENT cook times for roast — a difference of many hours.
So ask yourself if the roast in Miami is somehow less nutritious or digestible than the roast made in LaPaz. The answer is no.
And that’s because in both places, you cooked the roast until it was done and no longer. Both roasts had the same water loss. The only reason one took far less time to cook was that the higher air pressure meant that you could cook it at a higher temperature before you started losing too much water and overcooking the food.
I get that pressure cookers aren’t traditional, but neither is my convection toaster oven or my immersion blender. In all these cases, we’re just using technology to make our cooking more efficient.
It’s not “unnatural,” but wise to take our breaks where we can get them.
The fact is that the science shows pressure cooking is healthy, that it can preserve more heat-sensitive nutrients than any other cooking method because of its shorter cook times. The fact is that the difference it creates in the boiling point of water is well within the range of a normal difference on this planet.
Again, it’s the same difference we see between Miami and La Paz. If you used a pressure cooker in La Paz, it would mean that you were cooking your food in the length of time folks living in Florida take for granted. Would that be somehow unnatural or wrong? No. It would be like cooking in Miami! And La Paz isn’t even the highest city out there. There are plenty of others that exceed it in altitude by a mile or more. Their boiling points are even lower! Their cook times even longer!
Pressure cookers just use technology and a nifty trick of physics to act like a great equalizer. It just so happens that for those of us who live nearer to sea level, who aren’t used to adjusting recipes for altitude and pressure (unlike folks who live at some seriously high elevations), the difference in cook times seems somehow shocking and unheard of.
Thinking about buying a pressure cooker?
You’re not alone! I just acquired my first one and wrote a review of it here.
This post has been edited from its original content, in large part because of some interesting and stimulating Facebook discussions we’ve had about it. Basically, I just compressed the most salient facts from those other discussions into a new section titled “What about the argument that it’s unnatural or not traditional?”. I also clarified the meaning of a couple sentences elsewhere in the post. Thanks for all your help fine tuning this! You guys are awesome.
(top photo by sfllaw)