Pressure Cooker - What Happens Inside

Interesting! We commonly use alloys like hastelloy, waspalloy, haynes, and inconel for our jet engine parts, but they are operating at way lower pressures.

I presume there are major barriers separating personnel from the high pressure areas...

Try pipe itself, insulation and lagging. Is that enough barrier? Our plants are over 40 years old, and I am not aware of any steam supply pipe rupture, but due to issues with design of make-up water plant, there have been problems such that one boiler was condemned after a tube "window" failure.

seem like you've been to drinking session there buddy

You said "I suspect PF coal boilers operate quite a bit higher than 384 °C, and use a "steam engine" - a steam turbine"

Did you find any?

I had a general look and did not notice anything that fitted your thoughts!!

Can you post a link maybe?

http://en.wikipedia.org/wiki/Supercritical_steam_generator

Includes reference to the "Benson" boiler (just tubes, no steam drum vessel).

https://mitei.mit.edu/system/files/beer-emissions.pdf

ultra supercritical boiler is mentioned with regard to PF, also to IGCC/oxy, etc.

http://www.energy.siemens.com/us/pool/hq/power-generation/power-plants/steam-power-plant-solutions/coal-fired-power-plants/Luenen.pdf

details plans of plant being constructed for Cologne, Germany, and includes references to other ultra-supercritical steam units already in service.

Say, do you live near this? Check on it, and provide me with a complete intelligence report by Monday, please? Ha Ha just jokes, unless this is ultra-super convenient for you to do. I don't think steam is quite yet outdated.

Interesting point: the steam generators consist of vertical tubes, of such high pressure, there actually is no boiling, as the fluid simply goes critical (and then gets super-heated above that temperature by a large margin), so that there is no distinguishing phases any longer, no need to worry about departure from nucleate boiling either. This supercritical water is a dense fluid, much better heat transfer that conventional super-heated steam, for example.

My wife comes from Cologne, we live about 170 miles away (IS THAT ENOUGH?)

Yes, the blast radius for that system is probably no more than 0.5-1.0Km, depending on if fuel conflagration is involved, or "just" steam expansion.

In all actuality, these newer systems should even have shorter blast radii, than the older generation of boilers with multiple high pressure vessels, since the mass of liquid water above the flash boiling point (normal boiling point) is much less in tubing boilers.

I had to really work on that sentence to make it appear coherent. I hope it also appears thusly so on your end of the conversation.

Party, party buddy!!!

I see you got experience on teaching and I say you got also a talent to become a lawyer. haha, growing old wasn't bad after all, some get worst or even better rooted manipulator.

Hello Noudge79

I hope you haven't left us in anger or frustration!

I have certainly learned a great deal from this thread, and I would hope you have also.

Nothing I've learned here changes any of my thoughts or posts about domestic pressure cookers, but it has certainly broadened my knowledge about the use of supercritical fluids.

Although I am a longterm user of them, I never gave much thought to them otherwise. They cook hotter under pressure and I have some great recipes I have made for years and years.

I have learned enough to be VERY DANGEROUS NOW!! very interesting!!

Thanks to all.

Especially DKW, who can look here and learn more about his initials:-

DKW

Thanks to you, I have become an avid fan of Induction cooking. Unfortunately, their reliability has been way down on the scale of possibilities. I had to have my portable one replaced once, and my cooktop replaced once and then repaired around a year later. Fortunately I had purchased the extended warranty for the cooktop, and the portable was replaced under normal warranty. Also unfortunately, they are still quite expensive here in the USA. I have a good friend who just replaced his range (cooktop and oven in one unit), but it was over $1000 extra to get one with an induction cooktop, so he got a standard radiant cooktop.

Mostly due to the cost, I don't think I have persuaded anyone else to buy one, although I certainly have sung its praises to quite a few friends.

Thanks also for the DKW! I must confess that I was not aware of the DKW brand.

Interesting, I did not know that I had poisoned you so deeply with my love of induction cooking.

To your friend, just for the safety aspects of Induction, it was worth the $1,000.....or get portables for a tiny sum....they work just as well.....

I also had one portable unit that broke and was replaced immediately. My wife broke the glass top on one (don't ask!!), I still have it as spares, all the others still work fine.....I have two doubles and one single.

They even go with us camping....or at least one double does....we have a gas stove (and oven!) as well when needed.....

I am confident enough with what i have in mind 100%, no need.

What does that have to do with pressure cooker CM? Insignificantly, you get GA just by doing that?

Not my type to off topic people. I somehow respect the spirit of opposition.

Picture paints thousand words. Have a great and fun day learning.

Started a Joke by Bee Gees

the correct quote is "...,then why can't I paint you"

Answer : I'd probably run out of Lavender

English is perversely tricky, but not ambiguous

"and if you think you've had a nasty taunting this time."....some French knight

Noudge: definition of specific volume -

In thermodynamics, the specific volume of a substance is the ratio of the substance's volume to its mass. It is the reciprocal of density and is an intrinsic property of matter:

from Wikipedia. All matter may be considered to have a specific volume, as long as the temperature and pressure are defined. The specific volume of a liquid obviously changes only a small amount with temperature, however the vapor of that liquid may change by orders of magnitude, depending on the range in temperature and pressure involved. From http://enpub.fulton.asu.edu/ece340/pdf/steam_tables.PDF steam table, where T is in C units, P is in bars, V_f is in m³/kg (and also V_g)

T P(bar) 1000V_f V_g

100 1.013 1.044 1.673

120 1.985 1.060 0.892

Thus it is clear that specific volume does indeed change for the vapor, by about a factor of 2 through a temperature increase of 20 C. Please also note, the pressure in the steam table is for absolute pressure, not gauge pressure, thus when a pressure cooker is at the relief pressure (established by the weighed nozzle cover), that pressure is 15 psig, not 15 psia (absolute steam pressure is then near 200kPa approximately, and the temperature is about 120 C). Under those conditions 1 Kg of steam occupies approximately 0.892 m³ .

Yap James read or see figure on my top post. I know.

Nice sketch, oh i can see from volume=mass x spec. Volume, 0.005 m3/sec try to moves right side as mass is exhausted outside. Boiling should be a function of rate of mass of vapor exhausted. Since specific volume of gas is greater its mass will definitely minimal compared to the liquid. Work for the expansion of vapor is just equal to W=P(v2-v1).

There is nothing moving, rotating, or oscillating in a cooker, so any discussion of work or a reference to a work integral in connection to this is totally irrelevant.

here is a clear lid.. for your viewing pleasure.

fits only one make and model, no reason to have confidence in reliability, and unavailable

great

wonder if they are permanently out of stock because they keep failing

the sad fact is that I'm too bone lazy to hunt down a pressure cooker (signal wires should pass under a seal ring), encapsulate an emitter/detector (should take 122 degreesC), and see what happens

have to leave it to you, folks

Great, inputs amazing, I wish James Stewart could drop by and crank this thing up

Kulas: I am running a special this week on home pressure cooker limit tests.

Will you run the test for me? Please stand over the pressure cooker at all times.

weld the vent tube shut with silver solder. Place 0.5L in the pan, and turn the burner on the stove to high. Place the blocked lid on the pressure cooker, and observe carefully what happens when the safety plug blows out. I seriously doubt you or anyone else will ever see 200kPa gauge pressure on a normal, run of the mill pressure cooker. 100kPa corresponds to approximately 15 psig (pounds/square inch). The lid is approximately 10" diameter on smaller pressure cookers. 78.5 square inches at 15 psig gives a vertical force on the lid of 1178 lb-force. That will put your eye out.

On second thought, we recommend you send this over to Myth-Busters and let them have a "safe" go at it, do not try this at home.

As I recall, a pressure cooker is for raising the temperature at which boiling takes place in the vessel. And there is a difference between absolute and gauge pressure for those ill-informed on the site.

I have never ever seen a pressure gauge on a pressure cooker, it something that I would have paid extra to have, though my wife would hate it.....But she never uses it, she is scared of them.....

But what it does with cheap cuts is simply amazing, the flavours are also great.....

I cook up beef bones for the dog occasionally, just enough so that she cannot produce sharp dangerous slivers of bone....but she is not that bothered about bones anyway, prefers a branch off a tree to keep her teeth clean....

No companion is as loyal as a dog with ample supply of food, water, treats, and bones, and maybe that worn-out KONG ball he keeps chasing.

I wouldn't swear to it, but I think I recall a pressure gauge on the large (Ø ≈35cm?) pressure cooker my mother used for canning back in the '40s and '50s.

Canners did at least have a pressure gauge, and there was some control over the pressurization, as various pressure-temperatures are required for various foods canned by this method.

"...as various pressure-temperatures are required for various foods canned by this method."

Low acid foods preserved by the process rather that chemicals need to hit the magic 240^oF target and hold that temp for the prescribed time.

Here in Cheyenne WY USA we're at 6,000 ft above MSL. Here I need to hit and hold 15PSI in my pressure canner, where in Fargo ND USA (900' above MSL) I could pressurize to 12PSI and be safe.

If canning in Fargo and I brought the canner up to 15PSI, the increased temp would preserve the food just fine, but the increased heat tends to make the foods 'mushy', just like overcooking them on the stovetop.

American manufactured pressure cookers adhere to a standard for pressure canners set by USDA in 1917 - 15 psi

http://ulstandards.ul.com/standard/?id=136

Oh boy oh boy, nice testing buddy, sounds like your up to something James. Nasty sh*t right there. Myth buster sounds great. Wow, it sure is a heck of a topic.

Pressure cookers are for saving fuel.

The boiling point of water will rise with pressure, so the cooking will be faster.

However the best economy will be when the pressure is just below the level required for the weight to lift.

Cooking will be fast as there is pressure inside.

When no steam escapes, there is no loss of heat. ( every time there is venting the steam takes away a lot of heat energy.(think of the latent heat ))

If you can control your stove electrical heat you could save considerable energy.

You are correct, though on all the ones I have ever had, you could not see this "just off max" pressure....

I have always set mine up for the tiniest continuous steam loss.

If you know of a better method to achieve that "balance", please be so kind as to share....

I tried to send a similar reply this morning while having my wife's car serviced, but their WiFi didn't work for CR4.

None of the small (≈6L) pressure cookers I've used had any other indication of pressure besides the escaping steam, so if there is no steam escaping, there is no way of knowing whether there is pressure or not.

We always set it on high until steam starts to escape, then turn it down a couple of steps, start the timer, and wait for the timer to signal stop...

Yes you are right. It is not possible with domestic cookers. Though many many years back I had seen a "Presto" (?) cooker. This had a small rod of 3 mm dia. on the top

marked with green yellow and red bands. No steam escaped but the rod would project out proportional the internal pressure . Not very successful as you had to watch all the time and control the heat input.

Here most people listen for the "blow out of steam" and time it on the count rather than actual time. ( 4 for meat 3 for potatoes etc.) not efficient but ok for lazy guys watching TV.

The main purpose of a pressure cooker is not to save energy, but to attain high enough temperature to kill certain pathogens, notably botulism.

Did you mean the bacteria Clostridium botulinum, or the Toxins it produces?

Two different things!!!

As adequate safety with regard to Botulism Toxins is easily achieved by conventional pans, but at a slightly lower temperature (as boiling does it!) and of course longer cooking times, I somehow cannot agree that killing pathogens is a first priority for PCs (Pressure Cookers)!

I feel that most people use them for speedy cooking, or cooking of things that would take far too long are the two uses that spring to my mind first....hygiene is probably my last active thought.....its always a taken of course, but not my first thought I have to admit....

I have over the years used both Pressure Cookers and normal pans, neither I or any of my family have contracted botulism or anything like it!!!

In fact I have never much thought about Botulism at all since my schooldays.....I'm also nearly 70 y.o.

Was I (and my family) just lucky?

Looking on the web here:-

http://scienceline.ucsb.edu/getkey.php?key=1307

Gave me this:-

C. botulinum spores can be killed by heating to extreme temperature (120 degrees Celsius) under pressure using an autoclave or a pressure cooker at for at least 30 minutes. The toxin itself can be killed by boiling for 10 minutes.

Which tends to support my comments! In civilized countries, it appears that the bacteria Clostridium botulinum is very rarely seen........or we would all be ill or even dead!!!

Cooking everything in a PC for 30 minutes at 120°C, will make "mash of almost everything that I like to cook in such a unit!!! Most unattractive I find....

So how can this ALWAYS be needed....? As you tend to imply!

I even eat my steaks one level above raw!!! Very bloody..... ...and not done in a PC either!! A frying pan or a grill usually!! For only a few minutes on either side....

Thanks in advance for your reply.

It matters whether these are "canned" products to be stored for a relatively long time. For acidic items such as fruit, atmospheric boiling may suffice. Some vegetables, meats, and fish need to have pressurized boiling, with a monitored time-temperature cycle.

You appear to be talking about preserving, you forgot to mention that.

On maybe an industrial scale?

Isn't that a bit outside of using a PC at home, usually at any rate where I live and cook/preserve....

But even then, few who make home preserves do what you are saying. In fact, I do not know anyone who follows your advice in a private cooking/bottling/preserving situation.

Also, the final taste would be severely changed, to my mind, for the worst!!!

A good example being fruit juices and jams for example, after sterilising as you appear to mention/require/suggest, they would taste "cooked"....

So many use a "cold" steriliser of some sort for juices at least....here in good old Germany......the local chemist stocks them....and I don't "over" cook my jams either as I like a fresh fruity taste....

I have never ever even had problems with them "going bad" while still sealed up.......as I tend to add a few more °C than the minimum.....

What am I missing about using a PC at home? Please try and bring it down to a home /simple level as I am simply not following your line of thought here at all!!!

Can anyone else help explain what I am apparently not understanding with using a home pressure?

I am always willing to be wrong, stupid or even slow to learn.

No shame in any of that if true, but I always welcome a good, usable and logical explanation as well.....

Not yet had one......here at least.

Agreed. Botulism bugs are strict anaerobes, killed by atmospheric oxygen, so this only arises when food is stored in anaerobic conditions e.g. cans. There's no risk of botulism in food cooked normally for immediate use in a pressure cooker or otherwise, only if you're thinking of preserving it in say Kilner jars. Then you would be well advised to observe the 120°C for 30mins rule, or better still, don't try it at home. Industrial food canners are set up for it! I think I read somewhere that one spoonful (size not remembered) of botulin toxin could kill every person on the planet, so it's not to be trifled with. The canners sometimes make a mistake, about 30 years ago in UK there was a case in a retirement home where several old people (well about my age) died after eating tinned salmon. Gave rise to a "joke" at the time - what's pink and f**cks pensioners? John West salmon.

Tetanus is another strict anaerobe, and it's everywhere in soil a few inches underground. That's why an accident which stirs up earth and gets it into deep wounds is dangerous and you need a quick injection.

That's my take on it anyway.

As Andy said, I never give pathogens a thought when using the pressure cooker, unless canning, and I haven't done that in several years. Come to think of it, I remember my mom canning with a large pressure cooker, but that was at least 50 years ago. I haven't done that much canning myself, but I'm almost certain that I've done more than most California men, and I've never used a pressure cooker.

our two reasons for using the PC are to save time and to tenderize otherwise tough items. (^{Actually I don't use PCs; I use Macs!})

I just finished up a jar of jam that my mother-in-law made in 1985, and it was fine! It was canned in a regular deep pan, not a pressure cooker.

As Tornado said, it's preserving veg, meat and fish that's the potential risk. I suppose people have tried boiling it at 100°C and come unstuck. Fruit is less of a problem due to higher acidity which the botulin bug doesn't like.

It's not an issue when making jam, as it's not anaerobic. Only problem is mould, which doesn't harm anybody but wastes some jam scraping it off. My brother had that problem with his jam as he'd pour it into jars and leave uncovered overnight to cool, then put the lids on. What I do is drop the lid on loose immediately, and when all jars filled tighten them. Then listen to the satisfying clicks as the vacuum pulls the lids in. Bro now does that and no more problems.

So your post of:-

The main purpose of a pressure cooker is not to save energy, but to attain high enough temperature to kill certain pathogens, notably botulism.

Was simply a throwaway line that had basically little to do with the everyday usage of Pressure Cookers in private households......or more importantly, nothing to do with this blog!!

Let me correct you a little further as I see it and your comment:-

1) PCs in the normal home are NOT there as their main purpose to save the world from anything to do with Botulism. They might be used to sterilize some jams, fruit juices and the like, but Botulism, as you yourself said, has nothing to do with this....Though I personally do not use mine for such things. I have a special pan that can hold 6 quite large/tall jars and also a thermometer, to allow me to stage the sterilizing temperature process accurately....it seems to do the job to my satisfaction. Remember, some people do not even like using PCs or they are terrified of them. They should be dying like flies, poisoned, if your comment was even partially true!! Why aren't they?

2) PCs in the normal home are to my mind, mostly used to speed up the time to cook a particular meal/part of a meal. Something like Christmas puddings, tongue and many others things need dramatically long cooking times - hours sometimes, with a large usage of energy, to get them cooked correctly, using normal pots and pans. I also believe the taste is often better using a PC for many recipes, my personal rice pudding recipe is a prime example....far better than the conventional ones. And its fast too!! But it is simply not alone, many other recipes also benefit taste wise from using a PC.

3) PCs in the normal home are also often used to dramatically reduce the heat/power setting needed, but still cook faster, thereby also saving energy. Though this may not be the primary reason for usage by many, but my Scottish blood "applauds"!!! Am I alone, I really don't know, but the savings are there whether sought after or not!!

4) With a bit of thought and planning, I (and many others) can produce a nourishing meal/main course for up to 4-6 people, with all the components, cooked in separate "holders" in the PC, in record time, as compared to conventional pots and pans.....

There may be further reasons for using a PC that I am unaware of, or never learned or simply have forgotten.

But this blog was just about what happens inside......so you are off topic with your throwaway, unhelpful comments!

My comments are not "throwaway lines". They may not pertain to foods for immediate consumption, but they most definitely apply to long-term storage. Whether home canning of string beans (or other alkaline items), or commercial canning of fish and other meats, time-temperature curves are critically important. Your incompetent remarks might well prove dangerous.

I see your original comments as they were written, as only being really pertinent to industrial canning processes, and for the very few (I personally have NEVER EVER known anyone who canned meat and fish and the like since the '50s !) who nowadays still can their own meat and fish.

I had a quick look around on the web and found some good solid infos about meat and fish canning, most very old, but still of good value probably. The best appeared to come from the University of Minnesota, see here:-

food-safety-canning-meat-fish-poultry-wild-game

They managed to mention Botulism, to my mind seemingly fully and correctly, to alert anyone, on the page above, in even fewer words than you took:-

Botulism, which is the most severe form of food poisoning, is usually due to improper home canning.

That says it all, but it is a University page where education is first and foremost of course...

Cans and canning equipment, not necessarily just for meat and fish, appear to be available at specialist outlets....

Though whoever the people are who still can meat & fish themselves, I bet they often live a bit on the wild side in the USA - Alaska in particular comes to mind.... North of Scotland? It would be interesting to have contact with some of them, possibly living far away from super markets?

Certainly in Europe really few still do that as canned food of all sorts are so cheap nowadays and tasty, few it seems are willing to waste their time doing it themselves and probably costing more in the end, though one's own time should not really be counted financially as its a hobby!

I know a few older people who still have the equipment, but its rusting and getting dusty in the cellar.....nobody wants it.

As Botulism is a possible "effect" if canning is not carried out 100% correctly, the majority of people who don't do it themselves are possibly the "wiser" ones to my mind.

So I reiterate that your comments were OTT and as such being rated as a "throwaway" comment from myself.....excepting in that (written better of course, not as you wrote ), its always good to be occasionally reminded of possible "pitfalls" in "anything" from time to time....

I am sure that I and many others will never forget those "throwaway" comments for a very long time, which is of course really, really good!

Perhaps in reply, you could also answer the couple of questions I have posed in several recent posts, instead of simply ignoring them completely, as if you have no possible answer.....

Which is my personal take!!!

Thanks in advance for your excellent answers........

I wish you and all here, a great Easter Weekend, with no high winds as we have had for the last week here!