UPDATE: Visit our new section on pressure cooker nutrition, too!
We read available scientific literature and even contacted the researchers directly to find the latest data on the pressure cooker’s effects on vitamins and minerals to de-bunk three common pressure cooker nutrition myths.
MYTH: Pressure cooking destroys vitamins and minerals.
FACT : More vitamins and minerals are retained by pressure cooking vegetables as opposed to boiling and steaming. Saving and re-using the cooking liquid ensures the highest vitamin retention.
With a few exceptions, one which we note below, scientific data supports pressure cooking as one of the cooking methods that preserve the most vitamins1.
It’s important to note that, to date, we have not found a comprehensive study on the vitamin and mineral retention on a significant selection of pressure cooked vegetables. None of the studies we did find addressed steaming those vegetables in the pressure cooker – only boiling them under pressure. Research on the pressure cooker’s effect on food is a hodgepodge of studies conducted in different countries, laboratories and conditions, using just one or a few select vegetables that measure the effect of pressure cooking on just one vitamin, mineral or antioxidant.
A well done 2007 study published by The Journal of Food Science2 measured Vitamin C retention in broccoli using five cooking methods. The researchers pressure cooked broccoli at high pressure (15PSI/1 bar or 250F/121C) for two minutes and found that 92% of the vitamin C was retained compared to 78% retention for conventional steaming.
“Boiling and steaming caused significant vitamin C losses, 34% and 22%, respectively, while with the other treatments [pressure cooking, microwaving and microwave pressure cooking] more than 90% retention was observed.”
These findings contradict an earlier study published in the same journal3 that documented a high loss of antioxidants in broccoli after pressure cooking. However, the authors of this earlier study conceded that these nutrients were not actually lost but, instead, transferred to the cooking liquid.
Always keep and re-utilize the cooking liquid – it’s not only healthy, it’s delicious.
More Info: Broccoli & Pressure: the untold story of the better cooking method
MYTH: The high temperatures in the pressure cooker create carcinogens like frying or grilling.
FACT : Pressure cooking, unlike other high-heat cooking techniques, does not produce acrylomide or other harmful compounds.
Carcinogenic compounds develop in starchy foods, like potatoes, when cooked at temperatures above 120C/248F. Even though a pressure cooker could easily go over this temperature by 1-3 degrees C when operating in over-pressure acrylamides still do not develop- the pressure cooker’s moist cooking environment is the key.
A Swiss research team4 found that potatoes pressure cooked at high pressure for 20 minutes formed almost no acrylamides compared to other high-temperature cooking (25 versus 1500 μg/kg). And, by the way, potatoes need only 10 minutes at high pressure to be fully cooked- so, you’re safe.
Read More: Pressure Cooking Potatoes Turns Bad Starch Good
MYTH: Pressure cooking sterilizes food so there is no need to refrigerate leftovers that will be eaten the next day.
FACT : Bringing a pressure cooker to pressure will not sterilize its contents.
The pressure cooker has the ability to sterilize, but it takes time. Clinical sterilization can only be achieved by running a pressure cooker that reaches 15PSI at high pressure for 30 minutes5 – pressure cookers that do not reach 15PSI, like most electric models, will require even more time. Few pressure cooker recipes actually need 30 minutes of cooking time.
Pressure cooking food for less than 30 minutes is not going to kill any more bacteria than bringing food to a boil (212F/100C). However, just like boiling without pressure, bringing a cooker to pressure will kill most bacteria responsible for cases of food poisoning like, Salmonella6, Campylobacter7, Lysteria8 and E.Coli9.
But, seriously, don’t turn the contents of your pressure cooker into a bacteria petri dish! Follow the same safety guidelines for handling and storing pressure cooked food as for conventionally cooked food.
- Visit the new Pressure Cooker Nutrition section of this website, where we report on the latest research!
1Tips to Prevent Vitamin Loss; NutriPro: Nestle’ Professional Nutritional Magazine (Food N2 6/06; pg8) Retrived from http://www.nestleprofessional.com/united-states/en/documents/nutripro/2808_nutripro_2_cooking_meth.pdf
2Galgano, 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. doi: 10.1111/j.1750-3841.2006.00258.x
3Vallejo, F., Tomás-Barberán, F. and García-Viguera, C. (2003), Phenolic compound contents in edible parts of broccoli inflorescences after domestic cooking.; Journal of Food Science, Agric., 83: 1511–1516. doi: 10.1002/jsfa.1585
4Methods for Determining the Potential of Acrylamide Formation and Its Elimination in Raw Materials for Food Preparation, such as Potatoes; Official Food Control Authority of the Canton of Zurich; Retrieved from:
5Guideline for Disinfection and Sterilization in Healthcare Facilities, 2008; Healthcare Infection Control Practices Advisory Committee (HICPAC)Centers for Disease Control; Retrived from http://www.cdc.gov/hicpac/disinfection_sterilization/13_0sterilization.html
6V. K. Juneja, B. S. Eblen, H. M. Marks; Modeling non-linear survival curves to calculate thermal inactivation of Salmonella in poultry of different fat levels; International Journal of Food Microbiology 70 (2001) 37-51.
7Al Sakkaf A, Jones G.; Thermal inactivation of Campylobacter jejuni in broth; Journal of Food Protection 2012 Jun;75(6):1029-35.
8L. R. Beuchat, R. E. Brackett, D. Y.-Y. Hao, D. E. Conner; Growth and thermal inactivation of Listeria monocytogenes in cabbage and cabbage juice; Canadian Journal of Microbiology, 1986, 32(10): 791-795, 10.1139/m86-145
Wow! Very nicely referenced – it is so difficult to find quality, factual content online anymore.
So glad we have you to get to the bottom of it for us! The broccoli looks really nice, too.
Glad to do it. Posts like this are more work than whipping up a recipe, but I had tons of fun writing it and the scientists that wrote the papers I referenced were excited to talk about their research and to share it with us everyday-folk.
One of the reasons I almost always pressure-steam my vegetables is because it is likely the healthiest method, with less vitamins and other nutrients destroyed. As you point out, this is not easy to find in the nutrition scientific literature, as most comparisons either pressure-boil or pressure-steam for long times. A crucial point to highlight is that pressure-steaming retains many nutrients ONLY if short times are used (“aldente” textures). Both high temperatures and long times do destroy many nutrients, and thus there is a trade off in pressure steaming: the optimal retention is attained when the time is “short enough” to compensate for the high temp.
I agree, time is paramount in the pressure cooker! One has to experiment to find the perfect time for their veggies- that is why I always write my pressure cooker times in a range. My husband adores soggy lifeless veggies that just melt in your mouth – just like mamma made them. I love them with a little “bite” but not raw.
Hopefully a chem student looking for a thesis will tackle pressure steamed veggies!!
Great post Ms Mythbuster!
Hahaha… nice one!
Thanks so much Sheila.
I thought it was OK to leave out pressure cooked food. Won’t be doing it now. Bacterial colony?
Well you can, but you have to go through the canning process (which includes cooking the food in the pressure cooker in something like a Mason jar). You can’t just pour the cooked food into the Mason Jar and screw the lid on (well you can, but then it has to go into the fridge like everything else).
Most people that do canning will also have a specialized tool set (it’s not as intimidating as that sounded) that includes a tool to measure gap from the top of your food to the bottom of the lid (you need some but not too much air).
Even then most recipes (especially long storage) will require vinegar or some other acid to throw off the PH so botulism cannot survive.
If you have a garden (or even you would rather buy in season rather than out of season) and you want to keep your vegetables you can can them. I don’t know that an Instant Pot is big enough though, I use a 5 gal pressure cooker.
It’s good to know that pressure-cooking really does preserve the goodness in vegetables.
I always pressure-cook my vegetables and use the liquid at the end for making a gravy or stock. You could use a sieve or tea strainer to remove any bits of potatoes, broccoli etc as you pour the juices in the jug when making the gravy.
As for sterilisation – any thermal sterilisation requires enough time. Some microbes can still survive at 121°C, such as “strain 121” (look that up on Wikipedia). The only way to properly sterilise with wet steam is to use an autoclave at 134°C for the right amount of time. Only specialist equipment can achieve the right temperature and pressure and also remove all air and accurately time the process when all the conditions are exact, which you cannot do with a kitchen pressure cooker.
Thank you for your work Laura. :)
Fascinating! Thanks for sharing your uses for the cooking liquid – and expertise in clinical sterilization.
Would these same principles apply to pressure canning vegetables? Then the liquid the vegetables cook in would be stored along with the veggies. Probably just need to make sure to consume the liquid along with the veggies then.
I’d also be curious about pressure canning meats vs other forms of storage such as freezing. Does pressure canning damage or denature the proteins significantly more than other forms of cooking?
All great questions. I have not researched pressure canning and it’s benefits. But it’s a great suggestions to tack on to my list “to tackle”.
If anyone reading this has information or a link to share with porcupine, please do!
I’m afraid this article has a couple of errors… As stated by the first to comment the vegetables have to be just about cooked for the amount of vitamin retention you have quoted. How many people want their vegetables this hard ?
Also you have miswritten your own paragraph and misquouted the Journal Of Food Science.
You have said that they quoted just a 22% retention of vitamins for Broccoli after two minutes of boiling.
But what they said was a 22% ‘LOSS’ of vitamins. That means a 78% retention.
I am still going to buy a Pressure cooker after reading this article though.
Two minutes in the pressure cooker for boiled broccoli is quite enough to have them cooked – as you will soon see. I do advise steaming most vegetables to use the least amount of liquid and avoid pulverizing them (pressure steaming is more forgiving than pressure boiling)!
I have included the direct quote from the Journal of Food Science, what you saw was a transcription error in my introduction of it-which has been corrected.
I’m looking forward to hearing about your experience with your new pressure cooker!
Great info, genuine info. Thanks much.
It would be interesting to study the vitamin retention in vegetables which have been steamed in a pressure cooker at LOW pressure e.g. 5 – 8 psi.
I believe I’m correct saying that air inside the pressure cooker must be expelled before sealing airtight and bringing up to pressure, otherwise any remaining air will result in loss of vitamins and colours? Modern pressure cookers should remove the air automatically. On mine (a Fagor), the steam exits sideways underneath the yellow indicator to push-out the air, then the yellow indicator rises and the pressure builds to the level set on the dial.
No David, a pressure cooker does not intentionally remove the air. In my Instant Pot some steam escapes until there is enough pressure to close the safety plug thingy, and then further steam generated by heat creates the pressure used to cook. After reaching pressure, some steam may be released if the pressure happens to exceed the safety limit of the pressure valve. However, air or steam must be retained inside to create the pressure that raises the boiling point of water to create the heat that speeds up the cooking. I don’t believe there’s any intentional removal of air. (Or does the ‘safety plug thingy’ also function to delay the beginning of the rise in pressure, allowing some air to escape before the seal is made and pressure increases, to intentionally remove some of the air to reduce oxidation?? I’ve never heard that before, and doubt it, but I’m not an expert).
Then again, David, I take back my comment.
Looking around the web, including this site, it seems your right that pressure cookers do drive away oxygen while building steam. Learn something new every day. I thought that float valve thingy was just a safety feature, but perhaps it intentionally delays making the seal until steam replaces most of the air. I guess I should remember from using autoclaves that steam has a higher heat capacity and heats things faster than hot air does, so the primary purpose may be to reduce the cooking time, but it would also reduce the oxygen.
Thanks for teaching me that.
The Breville FSP, which has a motorised steam release, vents steam/air three or four times while it is building pressure. My assumption is that it is comparing pressure with the expected temperature. – it has both sensors – If they do not match, it vents to get a more steam rich environment.Thus raising the temperature for a given pressure.
I have an old stovetop pressure cooker with a v-shaped gasket in the lid, a small safety valve that is threaded into the lid, and a thick round quarter sized control with 3 holes spaced along the thick edge. The holes are marked 5, 10, or 15. The recipe book that came with it is full of recipes from bread, desserts, fresh fruits and veggies as well as frozen and dried, pasta, meats, meals. You must use the appropriate amount of liquid for the size of your cooker. When ready to do the pressure cooking, make sure the lid is on correctly, put the round controller with the proper pounds over the valve which is in the middle of the lid. Turn the heat up high and when you hear the control jiggle, it’s a noticible sound, turn the heat down to medium. You want between 1-4 jiggles per minute. Too many jiggles will expel too much liquid, not enough jiggles and it’s not building enough pressure. Start the timing at the first jiggle. When time is up, the pressure has to be totally released before you remove the lid. You can either let it depressurize naturally, or put it under cold water, or remove the control. Either way, always remove the control first before removing lid. The built in safety valve should not pop out unless you run out of liquid or the control got clogged and steam didn’t come out. Unlike boiling, you don’t need as much liquid because not as much is escaping because of the considerably shorter cook time. Makes perfect beef stew.
Thanks for sharing your experience with us, Diane. Come join us in the forums – we’d love to hear more about your beef stew!
Well I would just get a WAGNER
What is a WAGNER?