Coffee Joulies review: the effect is barely noticeable



In the spring, Cory and I both linked to the Kickstarter campaign for Coffee Joulies. Here was the promise of these intriguing metallic lozenges:

Coffee Joulies work with your coffee to achieve two goals. First, they absorb extra thermal energy in your coffee when it's served too hot, cooling it down to a drinkable temperature three times faster than normal. Next, they release that stored energy back into your coffee keeping it in the right temperature range twice as long.
Well, Marco Arment the creator of the fabulous Instapaper bought some Coffee Joulies and ran them through some tests. His conclusion: they aren't worth two dead flies.
I could do more tests with different conditions, but I honestly don’t want to spend another four hours to reinforce what seems pretty clear already: Coffee Joulies do work, but their effect isn’t very strong, and it’s nowhere near their claims that the drink “will be ready to drink three times sooner and will remain hot twice as long.” In fact, the effect is barely noticeable.

I imagine they’d fare well in an all-day test in a vacuum mug or bottle, but the effect is going to be similar to my insulated-mug test: an improvement, but not by much.

UPDATE: The makers of the Coffee Joulies have responded in the comments. They say, "We have run our own tests in literally dozens of scenarios, and the performance varies from greatly exceeding our claims to situations like Marcos"

Coffee Joulies review (Thanks, Jeff!)


  1. Okay, so this looks like about the same effect you get from using a more massive mug.

    I would vastly prefer whatever volume these things displace just be filled with hot coffee instead. 

    1. It’s not just a thermal mass.  It’s some kind of phase change material inside that  melts at 140 degrees, supposedly absorbing a large amount of heat energy in the process while not rising much in temperature  (cooling the coffee to the “perfect temperature”), and then releasing that heat by returning to solid state once the temp drops below 140, helping the coffee stay hotter. 

      Sadly, it seems it doesn’t have that much effect, which makes one wonder how much testing they did to see how well they work before making claims and basing a business around them.

  2. First, I would like to preface this by stating how much I love BB, its community, and acknowledge the various ways it has improved my life by introducing me to ideas and products that would have flown past my personal radar otherwise…

    But is this a bit damning in terms of BB’s contributors giving a “positive nod” (which, we all must honestly face the fact that a reference to something here is construed to be) to a product which wasn’t rigorously tested beforehand?
    I’m just curious as to how much money was garnered by the makers from readers here for what appears to be (to some degree) snakeoil. I understand that you guys want to (and do!) bring great things to us, but it leaves me with an unsettling feeling that you might give a somewhat tacit endorsement to something which later turns out to be hokum. Always keep in mind the influence you have and how most of us probably view your “thumbs ups”.

    Not ranting, just something to consider for the future.
    (and no, I didn’t contribute to the kickstart, so this isn’t subjective bitterness)

    1. If either Cory or Mark had said “Coffee Joulies work great! I use them! You should buy some!” that would be questionable, indeed. But that’s not what they said. Cory’s post was about how he tends to be dubious about whether Kickstarter project owners have what it takes to finish a project; Mark’s was just “people are contributing money on Kickstarter; I didn’t know coffee staying too hot was such a problem.”

      If somebody reads a post that’s basically “here is an interesting thing you might not be aware of” and interprets it as “you should GO DO THIS and GIVE THEM YOUR MONEY because I SAY SO and YOU TRUST ME”, that’s not BoingBoing’s fault.

    2. It *sounded* neat to me! But please don’t think that when I post about some interesting thing I come across that it necessarily means I vouch for it. It’s wrong to think that a mention of something on Boing Boing is a “positive nod” — that’s crazy! When I vouch for something, I’m clear about it.

    3.  damning? are you for serious? “Somewhat tacit endorsement”? Really?

      Seems you’re valiantly taking up the mantle for others who wish to make a point that you’re not actually willing to commit to, on their behalf… And you’re certain you’re not concern trolling?

    4. bbonyx, others above me have already commented about the fact that the initial posts weren’t ringing endorsements, but more of a “hey, look at this cool thing” type interest generators.

      Another thing that you don’t address in your post is that we are finding about about these test results from the very same outlet that supposedly duped us all into supporting the Kickstarter in the first place.  The fact that Mark has no qualms about posting followup info about a previously interesting thing that the site pointed out is pretty much the opposite of “damning”, don’t you think?

    5. I agree and did participate in the kickstarter and have had similar results.  In a mug they’re useless, in the vacuum mug i got from jouiles the coffee remained much too hot (for too long a period), though  in my dribbly plastic traveler it worked OK (-not well, but okay). I don’t blame BB because like them the concept seemed great. What BB was working with was only that premise. They’ve done the right thing in posting what amounts to a retraction, Dispite a possible back lash. This is how things should work in the real world, more often. I’ll praise them for being moral- though I can understand bbonyx’ & other detractors views. Every participant of online shopping or kickstarter programs know they’re rolling the dice because the premise is alluing. We all know what I’m talking about.  That rare album from a fishy ebay seller, that misleading amazon transaction- even RL shopping at a big box store when you tore into the packaging and couldn’t return it because it wasn’t “Like New” and got only store credit when they had nothing that might replace the item.  I don’t blame BB. They’re an agitator of things we’ll probably be interested in. Just like I don’t blame them for a post I’m not interested in.  Just my 2 cents

  3. The effect is not completely insignificant. Assuming coffee is safe to drink at around 145F (just made that number up) then with the joulies you can start drinking 8 minutes sooner. If it gets tepid at say 110F, then the joulies buy you an extra 15 min or so to enjoy your coffee. So its not too bad.

    The problem is that they take up all the space in your mug, so you’re likely to finish your coffee much sooner.

    1. With an insulated mug, it did seem they had a decent effect (if not what the initial claims were), but with a plain ceramic mug, they had hardly any effect keeping the coffee warmer.   The tester’s guess is that the mug’s heat loss through its walls, bottom and the air outstrips the Joulies’ heat return.

      It seems to me that instead of the “beans” you drop in a cup (which take up coffee space and could clunk you in the face if you tip the cup too far up as you drink the last of it),  it would have been better if they just made an insulated mug but with the same Joulies material lining the inside.  Then: insulated cup to maximize the effect, to no loss of coffee space, nothing extra to wash, and no heavy beans smushing your nose.

      1. Yes, heat transference. I’m not too familiar with heat radiating outward and the specific science behind it. But I’m pretty knowledgeable about certain materials and how they work in transferring coldness. Glass and metal are best for refrigerators, plastics are not very good at all, that’s why it’s easier to make whip cream in a stainless steel bowl pulled from the freezer, you can’t do that with plastic. 

        However, heat “circulates”, you can see it in hot liquids. Wouldn’t a heated object “circulate” the liquid contents it’s submersed in, thus  exposing more of the liquid to the cooling process? 

  4. I don’t use those thingies, but I do pre-heat my coffee mug with very hot water before I pour coffee into it.  At least that way, the mug absorbs less heat from the coffee.  Makes me wonder how the Joulies would perform if they were pre-heated with hot (or boiling) water.

    1. Yes, I would like to see that added into testing.

      1. Ceramic cup, room-temp
      2. Ceramic cup, pre-heated
      3. Ceramic cup, room temp w/o Joulies 
      4. Ceramic cup, pre-heated w/Joulies

      Now the entire thing, but with a lid. 

      There’s a reason “proper” espresso machines heat the ceramic cups atop the machine.

  5. I wouldn’t call this conclusive proof. Something that strikes me as odd is that the control cup of coffee took a half hour of sitting in the mug to get down to drinkable temp (145 f). I’ve never ever had to wait a half hour to drink a cup of coffee. This makes me think that perhaps the coffee I am pouring out doesn’t start at 195 f. If it has already come down from that temp to say, 160 f, then the amount of energy the gadget has to absorb is a lot less, which may improve its effectiveness. 

    1. This is an excellent point – although I’m not sure it would satisfyingly address the claim that the “joulie” should help to maintain temperature longer. Your model could explain why the “joulie” didn’t cool the beverage much faster, but couldn’t obviously explain why the “joulie” had so little effect to extend the time that the beverage remained hot.

    2. I agree. I’m from Seattle, I worked at many coffee stands and shops. The milk should be steamed “up to” 150. 

      Most people don’t know that milk, if heated at high temperatures, is no longer “milk”. So when the barista stares at a customer when they ask for their latte to be 220, (and sometimes burning the barista’s hand with a boil-over) essentially scalding or boiling the milk,  which should never ever be done. 

      Yes, I actively refused to heat milk to over 170. 

  6. I’m going to have to redo the experiment I did over the weekend. My fiance ordered a set of these, and 4 of them in a plain beer glass took boiling water straight out of the kettle to 140F in about 2.75 minutes. The same test without the Joulies required more than 18 minutes. I didn’t extend the test beyond 140F because I didn’t have time right then, but I’ll try to redo the test tonight and see how it goes.

  7. I thought Joulies were interesting when I saw the project on Kickstarter – I didn’t get there via boingboing – and I was *kind* of tempted. They’re shiny. And I drink coffee, often in job lots, daily.

    But then I figured I could just apply some (pre-boiled) money *directly to my mug* and cut out the middleman.

    That seems like a better option now. Thanks, Mark!

  8. Could the whole mug be lined with such phase-change material, and insulated from the outside? This, with a lid to reduce evaporative and radiative cooling from the mug surface, could improve the performance significantly.

    The phase-change material is the key; I wonder if the sodium acetate solution used in pocket heat packs would work there.

    Another possibility is a Peltier element attached to the mug, first cooling the coffee to drinkable temperature and then gently heating it to keep it there, inductively coupled with a power supply built into the desk.

  9. There are some things wrong with how this was tested.  I’m not saying the results are completely invalid, but let’s look at a few things.

    1. Start with “hot coffee.”  Okay, use water, but in that case at least make sure it’s not hotter than 196F.  As far as I know that’s like the reference temp for brewing, unless you’re doing something  special.
    2. Follow the instructions.  You do get 5 joulies in a pack, and it says you can use more if you think that’s merited.  I have to wonder how 5 would have fared in boiling water, versus 3 in a real-world test.
    3. Again, follow the instructions.  Joulies do next to no good in a ceramic / stoneware mug, as per the included documentation.  Using a thermally insulated container with no lid is hardly any better.  Figure out a way to measure temps with the lid on the thermal mug for this to be a valid test.  The lidded thermally insulated container is where these were designed to perform “as expected.”

    2 or 3 joulies in a lidded stainless Contigo works great for me with freshly brewed coffee.  The synthetic testing in the article is flawed.

    1. I use mine the same way you do: in my insulated thermos of coffee I take it work. I put two in and my coffee stay noticeably hotter for longer throughout the day. Hours longer. But yeah, in a ceramic mug in the morning it’s a wash.

  10. They stated specifically on their site that they work much, much better in a container with a lid. These results are basically on-par with what they advertised (for a lidless standard coffee mug). From their site:

    The better insulated your cup, the better Coffee Joulies work. Simply using a lid goes a long way. This is because less heat is lost to the environment, and more is stored within the Joulies themselves. In a ceramic mug Joulies will keep your coffee in the right temperature range for only a few minutes longer than usual (because mugs are such poor insulators – designed to keep your hand from being burned, not to keep coffee warm).

    1. mugs are such poor insulators – designed to keep your hand from being burned, not to keep coffee warm

      I’ve heard this several times from multiple people, and stated just like this, it’s a little confusing and calls into question my understanding of insulation. Is it just that mugs have a handle so you can hold them by a part that hasn’t become painfully hot? Because if it has nothing to do with the handle, where does the heat go if it doesn’t stay in the liquid and doesn’t get transferred to the mug (and from there, your hand)?

  11. i bought these, and have used them twice. i can verify – for myself, at least – that the effect is, in fact, barely noticeable. nice idea, but, i should have spent my money on crack, instead.

  12. I would hold off on damning these things entirely. The makers of these devices were using them themselves and thought that they worked good enough to try to make a business out of it. 

    Also, testing it in travel mugs without the lid is not a good test. What you need is to put the lids on and get some thermocouples snaked in though the pour/drink slits on the lids. Thermal transfer between the liquid and air, not to mention evaporation, will significantly cool down the coffee inside, as seen by the data.

    I should also note that I am still waiting for my joulies to be made/shipped and I didn’t get them to keep my coffee warm longer. After I make my double shot and 2 cups of coffee I put it in my travel mug. I can really only start drinking the coffee 2 hours later if I don’t want to burn my tongue. The data shown for the travel mug implies to me I might be able to drink my coffee sometime in the AM now rather than having to wait till around lunch time before I can take my first sip. but then again I could just be trying to justify my 40 dollar investment to myself.

    also, as a scientist I can say that the only conclusions are that in ceramic mugs they don’t seem to make much of a difference and that the travel mugs tests are inconclusive. And since they have been marketing to people using travel mugs since the beginning, and the reviewer basically said more testing was not necessary… why was this review presenting its self as science?

  13. We wish Marco used his Joulies a little bit more in his own coffee before posting what at first blush seem like a relatively detailed inspection of their performance. His Contigo test would have shown dramatically different results if he used the lid during the test. I’m also guessing that the cups may have sat undisturbed while being tested, which is fairly unrealistic, as the act of tipping a travel mug to drink from it will stir up it’s contents and will prevent the Joulies from nestling in the bottom of the tall mug where they can’t contact the majority of the hot coffee inside. As for the tests in the ceramic cups, as stated on our original page, the effects in that situation are measurable but modest. In that situation Joulies will definitely cool your coffee faster, but not much heat is stored since it cools so fast already. A better container is necessary to get the “stays hot longer.” We have some extremely satisfied backers using Joulies in this manner, but as Marco illustrated, that situation might not be right for everyone. We have run our own tests in literally dozens of scenarios, and the performance varies from greatly exceeding our claims to situations like Marcos. For example is fairly middle of the road. Marco’s review did teach us a ton about managing expectations and about the learning curve associated with our product. 

    1. While I hesitate to trust manufacturer’s claims without independent verification, you certainly make a good case that the tests performed were not the “use case” that you envisioned and that the joulies do work as advertised to make coffee drinkable sooner and keep it at a drinkable temperature longer. In the case of your tests, it’s drinkable half an hour earlier and for twice as long. To me, that seems worthwhile for those who are in the particular circumstance of drinking coffee out of an insulated cup with a lid, which is probably most folks who drive with a cup of coffee.

      Seems to me that bb needs to backtrack a bit on this article – one persons flawed testing is not enough to damn a product or company with.

  14. It seems a bit unfair to put out a hit piece on them if you’re not willing to go to the effort of rigorously confirming your data, or even buying a second thermometer.

  15. I like that the article update makes it sound like the effect is random; would it do that much harm to note from the beginning that this test only tests a scenario the makers don’t recommend?  I don’t feel I should have to read through most of the comments to get to that conclusion.

    Ultimately the test seems pointless, highlighting something that’s advertised.

  16. Well, I’m not going to read all those comments, so sorry if I repeat what someone else has posted. 

    Isn’t this the kind of product you’d want to use when you don’t have a decent mug? Or maybe even a mug that’s too well insulated? (I’m looking at you Thermos mug what keeps my coffee hot for 8 hours but too hot for one.) 

    It’s known that McDonald’s and other fast food places overheat their coffee. Then they put them into thin, poorly insulated polystyrene cups. It seems to me that in this situation these might be more valuable. 

  17. So there was this guy who did a test that confirmed exactly what the makers said about how -not- to use Joulies. 

    And then Boing Boing summarizes it as concluding they’re not worth “two dead flies”. 

    And then there was this part added later quoting the guy that makes ’em.  But not quoting the part about the tester only testing how -not- to use them.  Or even linking to the maker’s post 25 entries down in the thread. 

    And then all these readers came by who weren’t necessarily interested enough to read all the comments but did see the word “Joules” next to “Effect Barely Noticeable”.  Maybe, if they read real close they saw “not worth two dead flies” too. 

    Cool…now they know about Joulies!  Heh heh.  Dead flies!

    (They might see that vague, lukewarm added thing at the bottom about results sometimes being kind of sort of better and maybe they even considered wading through all those comments to see if there was anything more to it…but they got the gist.  And Boing Boing would have surely put the best argument there in that added rebuttal bit and…shit!  What’s that guy doing with that big wheat root up there????)

    Dead flies.  Heh.

  18. I use all 5 Joulies in a 20 ounce stainless steel, vacuum walled Contigo with a lid. My coffee is at or near boiling. My Joulies are at or near room temperature (76 at my place). I’m sensitive to very hot coffee, but I do absolutely find that my coffee is drinkable faster. It stays hot much longer; I’ve actually made coffee the night before, intending to drink it so I could stay up and work, gone to bed for a “nap”, and woke up 6 hours later with still-hot coffee. Even with opening and drinking during the day, my coffee stays hot to the very last sip (something that does not happen without Joulies).

    I admit I did hope that the Joulies would “manage” the heat of the coffee so that I could use them in any coffee cup, particularly a takeout coffee cup, but I knew that was not realistic in the present design iteration. The Joulies do work fine for me with my Contigo and the workmanship and materials are terrific. No worthless “magic beans” here.

    Reflect that we do have an analogous situation with cold, i.e. ice cubes. We all know the rules for ice cubes. If you want to make your drink cold fast, you need a lot of ice, and it needs to be in your drink. Those gel-walled mugs that you freeze do a poor job of keeping the drink consistently cold. I don’t think putting the phase change material in the mug itself would work because it doesn’t expose enough surface area to the liquid for adequate heat transfer to take place. If you have to “preheat” a mug before you add the coffee, you lose the whole “cool to drinkable” side of Joulies. If you don’t, then the inadequate surface area couldn’t work to keep your coffee hot. It sounds good at first, but after you reflect, you realize it’s barking up the wrong tree.

    Since Marco thinks his Joulies are worthless, I’d be happy to relieve him of them at his own valuation. I will even pay for the shipping.

  19. As someone who tries to live his life according to the scientific method, I appreciate the effort that went into understanding if these things actually work or are a crock.  If the creators of these things claim they tested them and received different results, then it is simply a matter of them producing their data to create a more suitable counter-argument rather then “Nah-Uh!”

  20. I got my Joulies a few days ago, and they work as advertised in a travel mug. I put all 5 in my 20 oz. travel mug and can drink my coffee within minutes. Got coffee this morning at 8:00, and at 10:00 was finishing my coffee at a decent temp. I have sensitive teeth, and travel mugs were darn near useless to me until this.

    Considering that now I can use a travel mug and my local coffee shop gives roughly a 50 cent discount for “refills”, (vs a 16 oz cup) in 80 days they’ll pay for themselves. YMMV, but I am very happy with the product.

    @ymendel Ceramic mugs transfer heat from your coffee to the ceramic where air carries the heat away. You’re exposing more surface area to air. Much like a heat sink absorbs heat from a CPU and then exposes a large surface area (cooling fins) to moving air. Double walled insulators have a vacuum (or other insulator) which does not transfer heat to the outside of the mug efficiently which keeps it “trapped” in your beverage.

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