home Forums Kitchen Chit-Chat Laura you are an evil, evil woman

Viewing 41 posts - 1 through 41 (of 41 total)
  • Author
    Posts
  • #22673
    Greg
    Participant

    I tracked down a copy of Myhrvold’s Modernist Cuisine today. It was in a library where I had browsing but not borrowing rights. I spent about 10 minutes reading the bit you suggested (p87). It was clear, concise and seems reasonable, but I am not convinced on why an induction stove under cooks when the PC is heated at full power. I will do some more thinking and start a new thread on the topic when I have it straight in my head. Even if I end up agreeing as there are clearly quite a few others interested. Then I spent another couple of hours reading and revelling. With more than a few “So that’s why!” moments

    You are evil because I am now seriously considering spending $AU700 on a cook book. It is marvelous. And should be compulsory reading for every professional chef. And serious amateurs for that matter. Actually it is not fair to call it a cook book. Yes there are some (quite a few actually) recipes. But it is much more about the science and practice of a kitchen.

    #22674
    Laura Pazzaglia
    Keymaster

    Yes, it’s a very nice set. : )

    Modernist Cuisine explains the “how” the trapped air causes a problem, as to the “why” the air remains trapped I got from a thermodynamics engineer at Kuhn Rikon.

    I can only interpret the facts to the best of my ability – although I am a science aficionado with an analytical mindset I cannot pretend to have a degree in the sciences.

    I do my best to share my experiments and conclusions to make pressure cooking easier. But I also openly share sources, facts and formulas for those who want to delve deeper themselves – the more the merrier!

    Bottom line: When using induction, bring your pressure cooker up to pressure on medium (not high) heat. It works.

    Ciao,

    L : )

    P.S. To anyone stumbling onto this topic, this is a continuation from the discussion on air being trapped in the pressure cooker, here:

    The Pressure Cooker Trouble-shooter

    #22682
    gteague
    Participant

    <head exploding>

    [g]

    /guy

    #22683
    Jonilyn
    Participant

    Well, another interesting avenue to follow. Just found these books in the local College in our city. Thanks Greg for sharing. Thanks Laura for as usual being the Saint of Pressue Cooking! (just saying Greg!)

    #22697
    Anonymous
    Participant

    I know I suggested this on the other page, but I will post it here as well…
    It would be interesting to see if there are differences from temperature tests inside the pressure cooker, when brought to pressure slowly (about 10 minutes) and when brought to pressure very quickly (less than 5 minutes).

    I wonder if trapped air lowers the temperature of the water, steam or both?

    #22700
    Anonymous
    Participant

    I had intended to open another thread entitled “Why is it so?” as a nod to a favourite science education program from my childhood. However Laura has created a link to here so here goes:

    From the other post:

    To summarise ->
    Observed fact: Food cooked in a pressure cooker brought to pressure at full power on an induction stove is under done if cooked for the recommended time
    Possible causes: (1 – 3 assume that the air has not been expelled)
    1. pressure is lower therefore temperature is lower. I think this is false
    2. temperature is lower because air at pressure is at a different temperature to steam at pressure
    3. steam is better than air at transferring heat to the food.
    4. the overall cook time is less because of the shorter time to pressure
    5. the pot does not heat up properly in the shortened time to pressure so heat that would otherwise go into the food is diverted into heating the container.

    First up, I had forgotten that my ex’s brother in law is an Emeritus Professor of Physics at the Australian National University. I haven’t spoken to him in more than 20 years, but I have put out feelers via my daughter. We will see what turns up. She also suggested contacting Heston Blumenthal and a few other people who are well known here, but probably not elsewhere. Still thinking about that. It is a scary thought. And Nathan Myhrvold/ Chris Young, if you follow this blog, feel free to weigh in.

    Let me also state that this is not about whether the observation is correct or not. People I trust, Laura not the least, have found this to be true. I do not doubt it. I do mistrust their credentials in physics however. I do have a science degree with a major in physics. Astrophysics specifically. I covered thermodynamics and the gas laws as part of the undergraduate program. But I haven’t used it in more than 30 years. Rusty is not the half of it.

    This is about understanding WHY it happens.

    In this first post, I will just elaborate on point one. Otherwise I will be up all night and this post will be the longest in the history of the forum. Even trumping @gteague. (:P) It may be anyway.

    1. pressure is lower therefore temperature is lower.

    This, as stated, is patently false. The pressure is set by the regulator on the pressure cooker. It doesn’t matter what is inside. If the (accurate) gauge claims 15psig, then that is the pressure of the gas inside. It doesn’t matter what the gas is.
    Laura however suggested that partial pressure could explain it. This carries more weight and it is certainly the reason suggested by Myhrvold.
    For those who don’t understand what I am talking about, barring a few caveats that are always present in science, partial pressure means that the pressure inside a sealed container is the sum of the separate pressures of the various gasses inside the container. So if for example the gasses are steam and air (Air is itself a mixture of gasses, but for simplicity I will treat it as a single gas) and if each are present in a ratio of 50% at a total pressure of 15psig. Then each individual gas is actually at a pressure of 7.5psig. So steam at 7.5psig will have a temperature of 235ºF (112ºC) (taken from Laura’s Altitude correction charts) rather than the desired 250ºF at 15psig. So the pressure cooker is operating at 235ºF. While we don’t know what the ratio of steam to air is, we do know that with the rapid closing of the valve, not all the air will have been expelled so the partial pressure of the steam will be something less than 100% and so the temperature of the interior of the pot will be something less than 250ºF (120ºC). Or so Myhrvold would have us believe on p87 of his amazing book.

    I disagree. First up, some evidence:
    Myhrhold, a few pages earlier (I missed the page numbers in my photocopies), talks about using spring regulated pressure cookers for canning. He states that one of the reasons not to use them is that because of the way they work, they do not vent all the air before they seal. Therefore according to the above, even operating normally they will run at a lower temperature than the pressure would indicate. However, if we look at the temperature log for the Kuhn Rikon review, it peaks at 247ºF (119.4ºC) Which is well above the temperature this nominal 12psig pressure cooker theoretically operates at. (Yes Laura, I know about the “above the line cooking” but without a pressure chart too, that is all I can go on). So, far from being below the theoretical value as it should be, it is actually above.
    Also, sometimes when I am cooking the valve pops up immediately the lid goes on, sealing the PC. If partial pressure was the culprit then I would expect these cooks to be underdone. I have not observed this.

    Second, some musings:
    If the temperature is determined by the partial pressure of the gas, then the air will be at a different temperature to the steam. To my mind, this is plain silly. Once the system has come to thermal equilibrium, everything will be the same temperature. So what is really going on? I would contend that the temperature is actually set by the boiling point of the water in the pot. Not the gas. The boiling point is set by the total pressure acting on the surface of the water. Not the partial pressure of the steam. Otherwise the boiling point at sea level in the Antarctic (very dry) would be lower than boiling point during a fog in London. As far as I know, this has never been reported. This total pressure is 15psig, and therefore the temperature will be 250ºF

    Third some mathematics. Sorry guys.
    The general gas law states that
    PV = KNT
    where
    P is pressure
    V is volume
    K is a constant
    N is the number of molecules present (Happy counting!)
    T is temperature

    For gas mixtures, this is true for each of the gasses in the mixture.
    So for steam:
    PsV = KNsT
    and for Air:
    PaV = KNaT
    And putting it together,
    Pt = Ps + Pa = (KNsT)/V + (KNaT)/V
    (I use t, s, a for total, steam air respectively)

    Note that both gasses occupy the entire volume. This happens in the real world because gasses are mostly empty space.

    If we now apply some basic algebra to the above, we get the following
    Pt = (Ns +Na)KT/V
    and solving for Temperature:
    T = PtV/((Na+Ns)K)
    If we use percentages for the number of molecules we discover that
    T = PtC/(50% +50%)K) = PtC/(100%)K or
    T = PtC/NtK

    So the Gas Law, even for partial pressures, predicts that the temperature depends on the Total pressure and the total number of molecules present rather than the partial pressures.

    How do we test?
    One possibilty…
    Take a pressure vessel, add some water and seal it. Now heat it until the pressure inside is 15psig. You will now have a mixture of air and steam inside as the air initially present will be unable to escape. Measure the temperature.

    Allow to cool, and unseal it (or use a second pressure vessel) heat the container until steam has been venting continuously for 10 minutes. This will remove all the air (Actually this is not guaranteed but it is the recommendation for pressure canners so it will do) Now seal it. Continue heating until the pressure gauge reads 15psig. Measure the temperature and compare with the first result. Repeat to get n average. The more times it is done the more certain the result will be. Note that because the vessel is manually sealed, the testing need not be done on an induction stove. Any source of heat will do. Also as we are looking at a difference, the pressure gauge and the thermometer don’t need to be calibrated but they do need to be consistent. and they need to be read at the same time.

    I lack the means to test. Laura has a logging thermometer so she would be able to measure the temperature, but I don’t think she has the pressure testing gear. Any volunteers?

    #22701
    Anonymous
    Participant

    Thanks for explaining that Greg. I know the temperature logging thermometer would get a false reading if it were to touch any metal parts. Are we measuring the temperature of the water, the steam or both? Are the water and steam at the same temperature?

    I believe the old-style pressure cookers, with weights, would require the cook to place the weight over the vent pipe only when plenty of steam is rushing out of it, to get rid of the air. Generally, the spring-type pressure cookers seal (and lock) automatically when the lid is (correctly) in place and the pressure setting dial is selected, however the pop-up mechanism can rise too quickly if the water is boiling too rapidly e.g. on an induction burner set too high or using an overpowered gas burner; this traps air inside.

    #22709
    Anonymous
    Participant

    @David I am on a tablet at the moment so will keep this brief. While a virtual keyboard is fine for short stuff an epistle like the one above needs a proper keyboard.

    Ideally you would measure both. However I don’t think it matters. The temperatures in the charts are actually the boiling point of water at pressure’ so it is this we are tracking. Once the system comes to equilibrium, the temperature should be the same in both water and gas. Reading both will confirm (or refute!) this.

    As for the weight system and venting air, this was another reason Myhrvold gave for not using a modern pressure cooker for canning. But this is a topic for another thread. In the meantime, I recommend you track down a copy of MC to read. I can’t say I will ever cook any of the recipes. They are way out of my league. But the rest I find more than fascinating. I still haven’t pulled the trigger on buying my own copy. I really can’t afford it. But I am already trying to justify it in my head by adding up the cost of multiple trips to the library to read it all. Sigh.

    @Laura,
    If we are making this the discussion thread, you really ought to change the title from the flippant one I gave it.

    #22722
    HelenAdams
    Participant

    First off I admit I don’t understand the math. But I will persevere.

    My experience with my cheap 1200 Watt IIRC induction burner and my Fagor pressure cooker has been positive.
    With 1 cup liquid or less I put it on high for 4.5 minutes. I lower it to setting 2 and leave it the remaining time. Seems to work fine with recipes from this site and others.

    With more than one cup liquid I am in no mans land. Adjusting 2-3 times.

    With smaller quantities my Fagor performs the same as my Instant Pot on induction. With larger quantities/more liquid slightly better.

    To make matters worse I am now about 3000 feet above sea level. Not that that is stopping the spring flooding.

    Not really adding to the discussion I know, but I am very interested in understanding it.

    #22727
    Anonymous
    Participant

    @Helen, this is NOT a rant against pressure cooking on an induction device. Many people use the combination and swear by it.

    What a lot of people, including Laura, have noticed is that food is undercooked if brought to pressure on full power, then cooked for the recommended time. The usual fix is to bring it to pressure on a lower setting if you have a high power induction burner and are affected by this. Your 1200W unit is probably not powerful enough to be affected. My unit is 2000W. I don’t actually use mine for pressure cooking, but for other reasons that are specific to my unit.

    This thread is an exploration of the reasons why it happens. The usual reason given is that because they come to pressure so quickly not all the air is expelled and as a result they end up cooking at a lower temperature. I disagree and the above post details why I think so.

    I may well be wrong though. And the discussion that proves my error will improve my understanding of the world. And that in my opinion is a good thing. If my opinion prevails, then other people’s understanding of the world will have improved. And that is also a good thing.

    In future posts I will be putting forward some other possible explanations.

    #22728
    Anonymous
    Participant

    I live at about 3000ft too. Have you noticed you need to adjust the timing of your cooks? I know I do.

    #22731
    HelenAdams
    Participant

    First I never suspected it was a rant. It is overall something I am puzzled by. Not just induction, but time to pressure etc. Bringing to pressure on high/med/etc. varies by devices and there are many variations. You have your induction, your ceramic, your gas, your electric PC, your campfire etc. Then their is your altitude and your quantity of liquid/food.

    Definitely I have had to adjust the time by double or more. Kind of embarrassing because I was showing off how fast the pot cooks.

    #22739
    gteague
    Participant

    does this apply to electrics? i guess it does if helen is in on the discussion.

    i’ve only cooked a handful of dishes and haven’t yet noticed anything undercooked. but i tend to look at the times and add 2-5 minutes depending on the amount of water and the number of ingredients and whether there is meat in the pot.

    but i’m not at all sure i’d notice undercooked if it wasn’t too raw to eat.

    /guy

    #22741
    Anonymous
    Participant

    @guy
    No it doesn’t. Helen has a stove top PC in addition to her IP.

    (Does that sentence jangle your IT background? :P )

    @Helen,
    I use a factor of 1.15. I have it on speed dial on my calculator I use it so often.
    Except for eggs. For some reason they take a lot longer to cook than the normal adjustment. Maybe my eggs are just bigger than Laura’s.

    #22742
    gteague
    Participant

    it’s either growing on me or wearing me down!

    #22744
    Anonymous
    Participant

    I am not ready to continue on to part two just yet, but I have a few comments to make on part one:

    Pressure.
    I have been talking about 15psig as though that is all that matters. It is not.
    What affects the boiling point of water is the TOTAL pressure on the water. This is the pressure supplied by the pressure cooker (nominally 15psig) PLUS the pressure supplied by the atmosphere. This is another 15psi (approximately) so the pressure on the water to effect a boiling point of 250ºF (121ºC) is really 30psi. If atmospheric pressure changes (for example with altitude) to say 12psi, then the total pressure is 27psi – the pressure cooker still contributes 15psig. This results in a cooking temperature of 243ºF (117ºC). It is a common and reasonable fiction to talk as though the pressure cooker itself is running at reduced pressure. This is not really true, and I think it is important for this particular discussion to be aware of the reality. That is why I was careful to use psig when talking about the PC pressure. This is “gauge pressure” and refers to what the PC itself is contributing.

    N (in the mathematics)
    If I am wrong, this is where my error will lie. At least I hope so. If not then the Gas Laws will be proven wrong after standing firm for about 300 years. And I am no Einstein.
    My assumption was that the total number of molecules will remain more or less constant regardless of whether it is steam or air or a combination in the mix.
    This may not be true. But I have no idea how to measure it.
    It is very easy to measure the (liquid) water. Just weigh it. Every 18.015g of water contain 6.02214129×10^^23 (That’s about 6 followed by 23 zeroes!) molecules. That number, very conveniently has been declared a basic unit called a mole. The same basic idea is used to count coins in banks these days.
    It is just a little bit harder to measure the number of molecules of air. Again just weigh it. A little trickier. What you need to do is weigh an open pressure vessel. Then seal it and pump out all the air. Weigh it again. The difference is the weight of the air inside the container. Then it is just a matter of looking up a few tables ( one for each gas – mostly Nitrogen and Oxygen but a number of others as well) to convert that to the number of molecules.
    What I cannot think how to do is measure the number of molecules of water vapour (steam) inside the test vessel. I am open to suggestions.

    #22745
    Anonymous
    Participant

    Trapped air must be a bad thing. I know steam sterilisation requires all air to be removed, see: https://en.wikipedia.org/wiki/Autoclave

    #22747
    Anonymous
    Participant

    David, I hadn’t considered the absence of air to be a factor. That is worth considering, and relatively easy to test. However is suspect that article is actually is actually saying that it is important only in that the presence of air reduces the effectiveness only in so far as it prevents the presence of a full head of steam.

    is very is very important to ensure that all of the trapped air is removed from the autoclave before activation, as trapped air is a very poor medium for achieving sterility. Steam at 134 °C can achieve in three minutes the same sterility that hot air at 160 °C can take two hours to achieve.[8] Methods of achieving air removal include:

    My emphasis.
    To test whether it is the presence of air that is the important factor, I would replace the air with another gas, say helium, the attempt to cook something using the helium/steam mixture and test for doneness. It would be expensive to do though. This scenario does add another variable though as we don’t know how food cooks in a helium atmosphere so it would also be necessary to check that.

    #22749
    gteague
    Participant

    you’re up early. wish i knew more about fluid dynamics (?) and boyles law (?) and the bournelli principle (?) so i could follow along better, if not participate by adding experiments and observations.

    /guy

    #22759
    Anonymous
    Participant

    Looking at the list, I realize I covered both 1 and 2 in my initial ramble.
    So I will move on to 3. And because it is closely related, 5.

    3. steam is better than air at transferring heat to the food.
    5. the pot does not heat up properly in the shortened time to pressure so heat that would otherwise go into the food is diverted into heating the container.

    Here, we run into David’s conjecture only in reverse. It is not so much the absence of air that is important, but the presence of steam. But less air means more steam given the concept of partial pressures I have already covered and given that the total pressure remains the same. This is a given as we are measuring the total pressure with the gauge.
    I think that these two ideas are at the core of what is happening.

    Water is much better at transferring heat than air. Anyone who has ever put their hand into an oven at 250ºC and tipped boiling water (100ºC – less than half the temperature!) from a kettle on themselves will attest to that. This is because the specific heat of water is very high. This means that for a given temperature water holds more heat than air, and can therefore transfer more heat to a cooler object. There is actually more to it than that, but I am trying to keep this simple.

    When it comes to steam, there is another very important factor at play. It takes a lot of energy to change the state of the water. This is a fancy way of saying boiling – changing water from the liquid state to the vapour state (steam). That is why boiling water remains at 100ºC (I am assuming sea level, open container) as it boils away. All that energy is going into the steam without any increase in temperature. The technical term for this is “Latent Heat” It is heat that is hidden from the senses (i.e. Thermometers).

    So steam has a double whammy of energy compared to air. It has extra energy stored as Specific Heat AND it has even more energy stored as latent heat. What happens when that hot steam comes in contact with something cooler? It gives up that heat of course. Some of it will come into contact with the sides of the pot. If the pot is cooler than it could be because the water heated so fast the heat from the burner didn’t have time to travel up the sides (Stainless steel is a poor conductor remember), some of the energy in the steam is transferred to the pot and not to the food. Resulting in food that cooks slower. If the sides of the pot are hot, this will still happen (the other side of the steel is in contact with air at room temperature) but it will happen to a much smaller extent. The rest of the steam will sooner or later come in contact with the food and transfer its energy to that food. HOWEVER all the air has not been expelled then there is less of that super energetic steam to transfer its energy to the food. Result? Food will take longer to cook. So if you do not change the timing, the food will end up underdone. Which is the observed result.
    Actually, I think I can dispense with #4 fairly quickly so I will tack that on too.

    4. The overall cook time is less because of the shorter time to pressure

    Laura, our guru of the PC, has stated explicitly, though not in each recipe, that she accepts that the food is cooking while pressure is building. She builds this in to the total cooking time by figuring it in as 50% time. That is if it takes 10 minutes to reach pressure this time is counted as 5 minutes under pressure. So if your pressure cooker takes 20 minutes to reach pressure you need to take five minutes off the given time under pressure [(20-10)/2)]. And more pertinently to the case we are discussing, if your PC comes up to pressure instantly, you will need to add five minutes to the time under pressure to get the intended result. So from a purely practical viewpoint, this is clearly a factor.

    Testing.
    I don’t think #4 needs to be tested. This is a practical adjustment issue and is clearly pertinent. It would be interesting to find out if making this correction is sufficient to completely fix the underdone issue. I have stated elsewhere that sometimes I put the lid on and the valve seals immediately. Under these conditions I have not needed to adjust timing. This has happened to me when the recipe calls for precooking in an open pot. Thus Laura will have made allowances for this and it cannot be taken as a counter example.

    #5 is very easy to test. Just measure the temperature of the side of the pot as soon as it comes to pressure. Use a pot brought to pressure on a conventional stove as a control.

    #4 can be tested. But for the life of me, I cannot think how. I do remember doing experiments on Latent heat, Specific heat and Sensible heat (the release of latent heat back into the environment when steam turns back into liquid) back in my university days, but I do not remember the details. Nor have I kept the notes. I am open to any and all suggestions. My gut feeling however is that this is the primary cause of the observed effect.

    #22761
    gteague
    Participant

    i’m gonna want two credits in physics when this thread is ended.

    but i’ll offer a brief intermission for comedy relief, but you have illuminated something that puzzled me just last night.

    we have a tv show here with a guy named mike rove or rowe who is also famous for narrating quite a few adventure/reality documentaries such as the hugely popular one about the alaskan crab boats.

    anyway, he has his own show where he goes out and joins some ‘common people’ for some activity. usually to work alongside them to demonstrate their job. and the shows are called ‘dirty jobs’, or ‘someone has to do it’ for a reason–he gets up to his elbows in muck on a regular basis.

    but his newest show for cnn is more that he goes to curious places and joins in with the folks at those places. and last night one segment was devoted to him visiting a russian sauna complex in chicago where he got the full treatment.

    now, i’ve had steam baths upon rare occasions, but i seem to remember the temperature being around 120ºF/48ºC to 150ºF/65ºC.

    but at one point in the show they noted that the temperature was 195ºF/90ºC and running low. so they appointed mike to open the oven door where the stones were and throw water on them to bring it back up to 210ºF/99ºC!

    now, i don’t know much physics or cooking, but i know that water boils at around 212/100 give or take some altitude. so how do these folks even survive? i’ve been puzzling over that for the last 24 hours. and i think you gave me the answer when you said that heat transfers much better from water or from air or steam. and it’s gotta be true in their case because if that was water temperature they would most surely be boiled.

    i just love coincidence/serendipity. jung loved it too, matter of fact.

    /guy

    #22764
    Anonymous
    Participant

    Actually steam burns are about as bad as they get. But in a sauna, you are in a fog rather than steam. Hint: if you can see it, it is fog not steam!

    When steam hits you it condenses back to liquid and all that latent energy is released into your body. Raising your body temperature and in the worst case scenario, cooking you. This is that “sensible heat” I mentioned but did not really go into. It is sensible because it can be sensed by a thermometer. Not because it wears flats. ;)

    It may be that the thermometer was measuring something other than the air temperature in the room.

    #22765
    gteague
    Participant

    ah! you’re right. could have been the oven temperature. i [ass]umed that since they read the temp in the sauna room it was the room temperature.

    and now you mention it, i remember from navy damage control classes that steam burns (which used to be really common when every ship had steam pipes running throughout the vessel) are truly horrible.

    /guy

    #22788
    Anonymous
    Participant

    Working through this (and doing a lot of physics revision along the way) has reminded of a discussion on this forum some time ago.
    A member by the handle of @tweakz was quite adamant that her (?) cheap weight regulated pressure cooker was more efficient than the more expensive spring regulated pressure cookers most of us here use. She wanted me to buy both one of her model pressure cooker and a whole pile of test equipment so I could prove her right. I declined. And she left in a huff. Possibly permanently. I haven’t seen her handle in quite some time.

    Anyway, looking at the theory of heat transfer as I have in the past few weeks, I think she may have been right. (Still not prepared to buy the test suite & pressure cooker though. If I had that kind of spare cash, there’s this cookbook I’d like to buy…)

    Because the weight regulated PCs vent steam more or less continuously, they should reach a higher steam partial pressure than my fully sealed Kuhn Rikon will. As a result, they should be more effective at transferring heat to the food even though they are both at the same temperature. Mind you, because it IS losing steam continuously, it will also be losing heat to the outside faster than my KR too. So the heat setting will probably need to be higher on the weight driven model.

    I guess it comes down to how you want to measure efficiency:
    Speed of cooking versus water and fuel usage. For me personally water use is very important as my water supply is the rainwater I collect from the roof. If I had a bunch of kids demanding dinner NOW!!! I might have a different opinion.

    #22980
    Anonymous
    Participant

    I bit the bullet and ordered my $700 cookbook. Gee thanks Laura. :P
    Actually I saved a lot of money. I found it locally for a mere $1200.

    I have joined Twitter and am currently stalking Heston. Once I am comfortable with the platform I will send him a tweet asking about this. Worst case scenario is that it will get ignored. Best case he’ll get intrigued and do the necessary experiments for a definitive answer. And become a regular here.

    #22981
    gteague
    Participant

    wow! once you get that one paid off here’s a relative bargain:

    http://amzn.to/1G6nk0F

    #22982
    Anonymous
    Participant

    Same cookbook. You haven’t taken the conversion rate to AUD nor the shipping into account.

    Nor the fact that a lot of web shops show a different price depending on where in the world you are ordering from. My daughter uses a virtual U.S. IP address to fool the system. Usually she only saves a few dollars, but in this case I suspect the savings would have amounted to “worth the trouble”.

    #22983
    gteague
    Participant

    so even though it’s my link, amazon shows you the aust price? or does it show the us price but convert it when you put it in your cart?

    here’s what i see:

    Hardcover $539.77
    Special Shipping Information: This item normally requires a shipping charge, but is eligible for FREE Shipping today.

    but if your daughter has a us ip vpn then she’s seen that already …

    that $1200AUS looks like 928.55USD on my conversion.

    #22984
    Anonymous
    Participant

    Yes. That’s what I see.
    According to XE.com. That becomes $AUD698.77 Near enough to the $700 I quoted.
    Especially since XE quotes commercial rates. I rarely see these reflected on my credit card.

    And every time I have believed the “free shipping” ad on Amazon, I have gotten as far as the checkout only to discover that the fine print says it only applies in the USA. Sometimes they are nice enough to include Canada. Sometimes they specify only contiguous states which I think means they exclude Hawaii, Alaska and the various dependencies like the Virgin Islands. This weight of book will probably come in at around $US100 to ship it to Australia. Possibly more.

    I actually paid $AUD685 from BookDepository in the UK. That did include postage.

    #22985
    Anonymous
    Participant

    I dropped it in the cart and checked the status of the free shipping. This is what it told me:

    Ship your items to a single U.S. address in one of the 50 states.

    I ran it though the checkout process. Here is what the free shipping actually is:
    Order Summary
    Items: AUD 724.99
    Shipping & handling: AUD 152.37
    Total before tax: AUD 877.36

    Even worse than I thought. And you’ll note that Amazon takes a chunk out for the currency conversion too.

    I just hope I abandoned the cart successfully.

    #22986
    Jonilyn
    Participant

    All,is not lost Greg. http://m.bookdepository.com/Modernist-Cuisine-Nathan-Myhrvold/9780982761007

    Free shipping world wide and 15% off. I buy from them often and am amazed how quickly books arrive to Canada.

    Good Luck.

    #22988
    gteague
    Participant

    ouch!

    #22997
    Anonymous
    Participant

    @Jonilyn,
    That’s who I did buy from.
    They are one of the sites that check where your IP is based and adjust the price accordingly. The price you see is not the same one I will see, and @guy will see yet another price. Even factoring in currency conversions.

    So their “free” shipping is just figured into the price. Which they adjust based on how much shipping will cost them. Which is fair enough. That’s why I don’t spoof my IP address. They still usually work out to be my best deal for books. And we buy a lot of books.

    #22998
    gteague
    Participant

    at that link i see:

    US$539.76
    List price US$613.59
    You save US$73.83 (12% off)
    Free delivery worldwide

    that’s one penny less than amazon for placement in search results i’m sure!

    #22999
    Anonymous
    Participant

    And I see:
    A$710.58
    List price A$794.54
    You save A$83.96 (10% off)
    Free delivery worldwide

    The price has changed since I bought it. Probably reflecting currency fluctuations.
    Using XE.com again, that means I would be paying $US552.50. As I said, they play with the price depending on your location. It is still significantly cheaper than Amazon for me.

    Of course, I could always buy it here and pay even more. Interestingly, that price has dropped by more than $AU100 in the last couple of weeks.

    #23497
    srb
    Participant

    I wanted to contribute some material to the discussion around the effect of trapped air on the operating temperature of the pressure cooker.

    This is illustrated in the graph of “cooking temperature vs percent air present” that I uploaded. The corresponding data are shown in the table above the graph.

    The chart is prepared using saturation vapor pressure data obtained from Engineering ToolBox.
    I assume a 2bar/120C pressure cooker. At 0% air the cooking temperature is of course 120C. At 15% air the cooking temperature is suppressed by about 5C.

    This is a well known effect industrially and the following link provides a nice introduction to steam use – and it describes the effect of air on steam temperature, see pg. 6.

    Hope this helps.

    #23499
    srb
    Participant
    #23502
    Laura Pazzaglia
    Keymaster

    Thanks srb! That is fascinating. May I share this with the other hip readers?

    Ciao,

    L

    P.S. The new post alert did not include the links either, I’m glad you came back to add them.

    P.P.S. Once you make a post in the forums, you have 30 minutes to edit it. ; )

    #23504
    srb
    Participant

    Of course.

    Sandro :)

    #23525
    Anonymous
    Participant

    Thanks for that @srb.
    Sadly when I fired up the big computer to look at it in detail I got the white screen of death. It may be a while before I can check it out in detail. I had a quick look from the iPad but it was pretty difficult.

    #24186
    Laura Pazzaglia
    Keymaster

    Hi everyone, I wanted to point out Sandro’s contribution to the just-published pressure canning guide:

    Pressure Canning Guide & FAQ: put ’em up!

    He adapted the chart he posted here earlier for pressure canning so I could more easily illustrate the point of why it’s important to exhaust your pressure canner.

    GRAZIE!!

    Ciao,

    L

    P.S. We’re a mixed lot of readers and participants – I appreciate that your generosity of shared knowledge in the interest of science.. and cooking!!

Viewing 41 posts - 1 through 41 (of 41 total)
  • You must be logged in to reply to this topic.