Peanut Butter Is a Liquid

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Your humble blogger feels the need for a wee change from our usual programming. Yes, the Ukraine conflict is important and even riveting if you are a war porn sort…but how often can one ring the changes on “Russia will prevail?” And as far as the slow moving bank crisis is concerned, the Fed could stop it by lowering rates, or even just pausing, since they caused it by increasing rates too quickly. The fact that they aren’t suggest they are encouraged that bank use of their emergency facilities dropped a lot. But the Financial Times among others begs to differ.

So let’s talk about important topics. We know cats are liquid:

As the piece below discusses, the TSA has forced the question of whether peanut butter is liquid. Perhaps you can claim your super chunky peanut butter isn’t liquid, but as a general rule, it is.

By Ted Heindel, University Professor, Bergles Professor of Thermal Science, and Director of the Center for Multiphase Flow Research and Education, Iowa State University. Originally published at The Conversation

Those Transportation Security Administration requirements are drilled into every frequent flyer’s head: You can carry on liquids that are only less than 3.4 ounces (100 milliliters) in volume each.

But when the TSA recently confiscated a jar of Jif under this rule, peanut butter lovers were up in arms. Some skeptics of security may suspect hungry officers just wanted to make their own PB&Js. TSA, however, contends that peanut butter is a liquid – and a full-size jar of Jif is over the 3.4-ounce limit.

Just like Americans’ favorite legume-based sandwich ingredient, the story – and the outrage it inspired – began to spread. However, I’m a mechanical engineer who studies fluid flows, and the TSA action made sense to me. By the scientific definition, peanut butter is indeed a liquid.

First Consider fluids

To define a liquid, we must first define a fluid. Any material that flows continuously when a shearing force is applied is a fluid. Think of a shearing force as a cutting action through a substance that causes it to flow continuously. For example, moving your arm causes the surrounding air to change shape – or deform, to use the physics term – and flow out of the way. The same thing happens to water when your arm takes a swim stroke.

There are many kinds of fluids. Some act very predictably and move smoothly, as air or water do. These are called Newtonian fluids, named after Sir Isaac Newton. Scientifically, a Newtonian fluid is one in which the shear force varies in direct proportion with the stress it puts on the material, known as the shearing strain. For a Newtonian fluid, the resistance to fluid flow – that is, its viscosity – is constant at a given temperature.

Shearing forces push a material in opposite directions, producing shearing strain. Designing Buildings

Other types of fluids do not move quite as smoothly and easily. For some, like peanut butter, a minimum shearing or cutting force may be needed to get it flowing, and it may vary nonlinearly with shearing strain. Imagine you’re stirring a jar of peanut butter. If you stir really fast, with more shearing force, the PB gets runnier, while if you stir slowly the PB remains stiff. These types of fluids are called non-Newtonian fluids. Peanut butter may stick more than flow – maybe you could consider this movement more chunky-style.

Peanut butter is actually a great example of a non-Newtonian fluid because it doesn’t flow as easily as air or water but will flow if sufficient force is applied, such as when a knife spreads it on bread. How easily it flows will also depend on temperature – you may have experienced peanut butter drips after slathering it on warm toast.

Strange Fluids Are All Around Us

Our everyday lives – but not our airplane carry-ons – are filled with substances that are unexpected fluids. In general, if it can flow, it’s a fluid. And it will eventually take the shape of its container.

Some surprising fluids are peanut butter’s kitchen neighbors, like whipped cream, mayonnaise and cookie batter. You’ll find others in the bathroom, like toothpaste. The natural world is home to other strange fluids, like lava, mudslides, avalanches and quicksand.

Gravel can be considered fluidlike. The individual particles are solids, but a collection of gravel particles can be poured and fill a container – its what’s called a granular fluid, because it has fluidlike properties. The same can be said for cereal poured out of a box or sugar into a bowl.

The body of a fully relaxed squirrel counts as a fluid, flowing to fill its container. Ted Heindel, CC BY-ND

Traffic flows on a busy highway, and people flow out of a crowded sporting venue.

You could even consider a cat lying in the sun to be a fluid when it has flattened out and fills its containerlike skin. Sleepy, relaxed dogs, squirrels and even zonked-out babies can meet the definition of a fluid.

Liquids Are One Type of Fluid

Now, you might be objecting: But, the TSA didn’t call peanut butter a fluid, they said it’s a liquid!

Fluids are divided into two general categories: gases and liquids. Both gases and liquids can be deformed and poured into containers and will take the shape of their container. But gases can be compressed, while liquids cannot, at least not easily.

Peanut butter can be poured into its container and then it deforms, or takes the shape of that container. And every 5-year-old knows that peanut butter does not compress. When they squish their PB&J or peanut butter crackers together, the peanut butter does not smoosh into a smaller volume. No – it squirts out the sides and onto their hands.

So, the verdict on peanut butter: delicious liquid.

If you plan to make a PB&J sandwich midflight, count on bringing less than 3.4 ounces of liquid peanut butter. And the same goes for its liquid cousin, jelly.

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  1. lyman alpha blob

    OK, so what’s the TSA position on glass?

    Try going through security with peanut butter in a glass jar and you could hold up the line for hours. Or maybe eons if TSA waited long enough to see actual evidence of glass flowing before deciding whether to ban your receptacle or not.

    Maybe that’s the monkeywrench needed to bring the whole TSA stupidity regime down!

    1. Amfortas the hippie

      aye. glass was top of mind since i saw what this was about.
      ive got a few 100-120 yo windows in my house…saved from remodels and even purchased at an antique store.
      before i framed them in, and could get a finger and thumb on opposite sides, one could feel that it was thicker at the bottom.
      wife and boys didn’t believe me when i informed them that glass was a liquid…had to resort to a materials science website.

      but, none of this matters to me…i’ll never set foot in an airport again.
      i’m, as far as i know, still on a list…from my incessantly yelling at my employees(congresscritters) during Bush2….and i’ve got a bunch of metal in me, and always set those machines off.
      hassle all the way around.
      and i loathe flying anyway.
      haven’t flown in more than 30 years.

      1. Michael m

        Sorry but old windows are thicker on the bottom because old plate glass was uneven and always set with the thicker end down. Too viscus at room temp to behave like a liquid even if it is non-crystaline.

        1. Piotr Berman

          OTOH, I was told that stones in old Inka walls have such perfect fit in part because they had good fit from the start, but in part because the stones flowed a bit under heavy weight over hundreds of years.

  2. tevhatch

    Good luck with a kilogram of ice. Meant to go under lyman alpha blob at 10:27. but for some reason reply does not work right for me today.

  3. Clonal Antibody

    No the TSA, and the author are wrong. Technically incorrect. Peanut butter is a suspension in a liquid, solid particles suspended in a liquid, the said liquid being peanut oil, or sometimes palm oil. A jar of peanut butter would contain far less than the 3.4 oz of oil. Even in a large jar.

    1. Dida

      True, but fluid suspensions like honey, mud and peanut butter can be modelled as viscous liquids under normal conditions (everyday life). In different circumstances, different models are needed.

      Approximating suspensions as viscous liquids works well, but only at certain scales. “At some point that’s going to fail,” Sauret said. “And we need to be able to say, ‘at this point you cannot use this approach, and instead you need to use a different method.'”

    2. Grumpy Engineer

      Yes, I agree. Peanut butter is mixture of oil (peanut oil) and solids (peanut proteins) that is better categorized as a paste or a grease. Most greases are mixes of oils (typically silicone or hydrocarbon) and solids (typically soaps, clays, or mineral powders). Heck, peanut butter is the classic example of an NLGI 2 grease on the industry standard NLGI “grease consistency” scale:

      But on the other hand, the actual TSA rule (at reads as follows: You are allowed to bring a quart-sized bag of liquids, aerosols, gels, creams and pastes in your carry-on bag and through the checkpoint. These are limited to travel-sized containers that are 3.4 ounces (100 milliliters) or less per item.

      Even if peanut butter isn’t a liquid, it would definitely qualify as a paste. So restrictions on peanut butter aren’t a surprise. And it makes just as much sense as restricting water bottle sizes.

    3. Luckless Pedestrian

      I believe peanut butter is a colloid. I don’t think you can filter out the solids. If something is a suspension you can filter out the solids.

      1. Ernie

        I don’t know about filtering, but if a jar of pure peanut butter (i.e., made from nothing but peanuts) sits on a shelf long enough (either in the store or at home) the peanut oil will separate to the top of the jar and you have to mix it to make it spreadable again.

        1. ambrit

          We encounter that problem with almond butter. Phyl pours off the palm oil and mixes in coconut oil instead.

      2. Grumpy Engineeer

        The solids can be filtered out. Both peanut oil and peanut powder are sold in grocery stores worldwide. You can press peanut butter at extreme pressures to get the oil out, or you can boil it and skim the oil off the top. Residuals are usually leached out with solvents (often n-hexane, though non-petroleum alternatives are being investigated).

  4. JohnA

    I recently flew back to England from an airport in the south of France. I took some cheese in an opaque zipped bag with a sleeve containing a frozen freezer pack. At airport security, the bag was removed and the freezer pack confiscated. It had been no more than 30 minutes out of the freezer and permanently sealed. The guy claimed it was a liquid and not allowed. At least he did not confiscate the cheese. I had flown with the freeze pack many times before unquestioned.

  5. Casual Observer

    I believe that technically glass is a fluid (really old windows are thicker at the bottom). Will TSA be confiscating glass objects >3.4 ozs. next?

    1. c_heale

      I read a long time ago this is not true. The window makers put the thicker glass at the bottom of the window, to lesson the number of breakages.

      According to a reference I just checked glass is an amorphous solid (the molecules are not aligned), unlike a crystal (the molecules are aligned).

      Glass is not a liquid unless it passes its melting point.

  6. Fred

    I worked in the pump industry and every once in awhile someone would try to use a centrifugal pump for a non-newtonian fluid like peanut butter. Trying to explain it was difficult, because you are basically telling him that his purchase of a $500+ pump was useless.

    1. davejustdave

      Jif is a brand name used for both peanut butter and peanut butter spread – Natural Jif creamy peanut butter spread contains 90% peanuts.

    2. JonnyJames

      lol, it’s a peanut butter product, with stabilizers, hydrogenated oils, sugar and other added stuff. Sugar is added to almost everything in the US.

    3. Mildred Montana

      For those who don’t buy peanut butter regularly, it is one of the many products nowadays which have been crapified. I speak of “natural” peanut butter, just peanuts and peanut oil and salt. Not those so-called peanut butters with hydrogenated oils and loads of sugar.

      Up until a few years ago one could grab just about any natural peanut butter off the shelf and know it was okay. Today most makers have so reduced the peanut content and increased the oil content of their product that nearly every one of them drips off the knife like syrup. Don’t risk trying to spread them on your toast. Just up-end the jar and pour. That’s how bad they are, and I do not exaggerate.

      Of all the brands available (here in Canada, I should say) there are only two I will buy. They at least haven’t been crapified. Yet.

    4. Arizona Slim

      Nope. It isn’t.

      Want good peanut butter? Make it yourself. Dry roasted nuts and a blender like VitaMix (which I have) or Blendtec. Boom. Done.

  7. Louis Fyne

    If you’re willing to sacrifice an old speaker for the sake of science and little kids….

    take an old speaker, put some non-newtonian fluid on it (or in a thin bowl on the speaker). Play some bass-heavy music and watch kids have fun.

    (thank you QI and Stephen Fry)

  8. digi_owl

    Reminds me of an early STTNG episode, where they encounter some entity that classify the crew (with one particular exception) as “bags of mostly water”.

    1. Thomas Neuburger

      “Ugly bags of mostly water” is the line. Rolls right off the tongue.

  9. irrational

    A few years ago, we bought some Spanish soft cheese on a weekend visit, where we only had hand luggage. At the airport did it occur to us that security might not be happy even though cheese is not a liquid. We made sure we asked before going through the check point and kept family waiting just in case we’d have to give it up. They relented – I suppose because we were taking back a local culinary delicacy ;-)

  10. Susan the other

    But just imagine if peanut butter had no jar. The damn stuff would be everywhere. Can’t have that. Peanut butter steering wheel. If peanut butter were a sovereign currency it would not only be in jars, it would also be FDIC insured… to maintain its liquidity. Or contain it. Same thing maybe. And if peanut butter is neglected and allowed to just spread all over it’s just a mess. Nobody could invest it for a profit. Peanut butter needs to have an element of scarcity because, just like crypto, it’s essentially valueless. So it makes sense to classify it as a liquid, put it in jars, fiat a reasonable value for it and consolidate the distribution of it. Preferably with a TBTF peanut butter bank.

  11. Dida

    On a tangent: Lambert, confess, you picked the article only for the opportunity to show the prowess of cats at being the octopuses of dry land. Thank you: for this lover of dogs it was not only hilarious, but enlightening too! I wonder what happens with their skull bones though; the skull must appear much bigger to us than it actually is.

    Lastly, you don’t need to justify posting peanut butter and cats by minimizing the significance of the Russian conflict. We all need breaks from the collapse of the world order. And I have to protest (vehemently!) the notion that I find the conflict ‘riveting’ because I am ‘a war porn sort’ of person. That one felt quite offensive. Capitalism is crumbling around us – again! Last time when this happened 60 million people died – and we didn’t have nuclear weapons. But if the current and coming wars between Russia-China and the West don’t scare you, what can I say, maybe you nurture a secret longing for world annihilation.

    1. digi_owl

      The tentacled ones have been known to travel over land from time to time.

      One such story involved an individual traveling between aquariums for a night time snack.

      1. B24S

        Used to work at the California Academy of Sciences. Over in the aquarium they had to lock the octopus’ tank, as it had a well earned reputation as an escape artist. Even had to cover the drain, lest it disappear with no trace.

  12. CGKen

    Slightly off tangent but the US gov sells $1000 peanut butter.

    It’s a standard used for testing as this blog relates.

    At first glance it might seem a “waste of taxpayer money” but NIST must be one of the biggest bangs for the buck in the federal government.

    1. Susan the other

      I found, via the internet, that peanut butter is an excellent medium for removing tape residue from wooden surfaces. Because it is sticky and stays put while the oils soak into the wood a bit and then it can be scraped off with a stiff Teflon spatula. Then apply finishing oil.

  13. John

    Interesting discussion but anything TSA does falls under the general rubric of Security Theater.

  14. Jeff W

    “TSA, however, contends that peanut butter is a liquid…”

    which I learned about the hard way, over a decade ago. Back in 2012 I was traveling to Japan to visit my US nephew who was there for a few years. What special thing did he want from home? Peanut butter, what else?

    Well, the ever-vigilant TSA official in the security line nabbed the two jars of Jif (it was, as I recall, Jif, not Skippy) in my luggage, saying their contents was a liquid. There was no air of self-satisfied triumph—he was almost apologetic about it, asking if I didn’t want to take the jars back out to someone outside the security cordon but, of course, there was no one. The person who had brought me to the airport had long since left the scene of the crime.

    I was pretty philosophical about the whole thing—peanut butter, after all, could be an extremely viscous liquid, the man had a job to do, and what’s a day at the airport without being tripped up, in one way or another, by the some absurd occurrence, anyway?—that is, until now, when I realize that I passed up my 15 minutes of fame by not getting on social media and telling the world of this event. More than a decade after the incident, I am racked with regret.

  15. A guy in Washington DC

    I believe that the Jiffo-Ukrainian situation and the videos from the feline front are linked.

    The Ukraine front lines may appear to be solid, but as the ground heats up this spring the front will become more fluid and that could eventually lead to a volitile political situation. However if the Chinese act as a catalyst and the BRICs apply enough pressure, a new phase may be reached and the Ukraine will again crystalize into a frozen conflict, things will have time to cool down and we can avoid a catastrophy.

  16. Piotr Berman

    Liquid rule was introduced because of liquid explosives. It reminds me when ca. 45 years ago I had to go to Prague for a day from Warsaw, and a friend who was doing chemistry experiments asked my to bring a bottle of sulphur acid, because chemistry stores in Warsaw had only a more diluted variety. So I returned with a liter of concentrated sulphur acid in a glass bottle in my little on-board bag. I was careful not to break it…

    Kind of like a scene in Kill Bill where some passengers on the plane to Tokyo sit with katanas at their belts.

    Can one formulate an explosive mix with peanut butter?

  17. kengferno

    I had a jar of local honey confiscated by TSA. I was arguing with them about it as it was a gift from my friends who I had visited. I took the top off and held it upside down. The honey didn’t budge. I said it was a gel as it jiggles, but didn’t flow. (It was VERY thick honey). She did NOT think what I was doing was scientifically accurate, grabbed it out of my hands and said if I didn’t shut up I was being arrested. A guy next to me put his hand on my arm. “It’s not worth it, buddy”. I just turned on my heels and left. I waited and thanked him. He and about 4 other people who witnessed it all said that it was hilarious and stupid and they totally felt my pain. Weird experience.

  18. chris

    Thanks for the interesting diversion. You’re right about things lately. I feel like there are LOTR memes that speak to “being on the edge of a battle you can’t escape…” that’s how this time feels. Everywhere.

  19. tbob

    I survived Viet Nam on peanut butter and Kool-Ade sent by my parents. As a helicopter recovery crew chief, on call 24/7, I had very few opportunities to avail myself of the mess hall’s regular meals. But there was always freshly baked bread to be stashed onboard the Huey. Kool-Ade cut the chemical taste of “Potable Water” airlifted into the various fire support bases.

    How can something that sticks to your ribs be considered a liquid?

  20. fjallstrom

    It’s all security theatre. If I remember the origins correctly, British security services infiltrated a group of young Muslim men and got wacky ideas about liquid bombs going. Then when the cops had arrested them, a meeting of EU transport officials was held. At the meeting there was a rumour that the US would ban any fluid container larger than 100 millilitres, and hence the meeting adopted that rule. The US promptly followed with the same rule. There was never anything resembling reasoning as to how and why this rule would make anything safer.

    In order words it shouldn’t matter if peanut butter is a fluid, it shouldn’t be confiscated at airports.

  21. redleg

    The problem is not whether or not peanut butter is a liquid. The problem is the TSA.

    1. some guy

      And the people who created the TSA to begin with.

      Unfortunately, abolition of TSA and restoration of all the previous departments and agencies which were mashed together into a TSA . . . . along with restoration of the Union status of all those previous departments . . . is the only solution to the TSA problem. That would be politically difficult to achieve, especially since the Deep State’s False-Flag Professionals would be ready to stage as many terrorist incidents as needed to get the public to beg for TSA’s recreation all over again. Maybe using another batch of anthrax.

      It would be easier to pass a law stating that ” peanut butter is a soft solid” for TSA purposes.

  22. Cetra Ess

    I think the author may have some bad peanut butter. No peanut butter I know can be easily stirred. And if you take a spoon and scoop some, it doesn’t leave the spoon when upside down. If your peanut butter is in liquid state then it’s peanut juice. But, you know, you must comply. It’s three lights, not four.

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