Coffee Joulies: clever coffee temperature regulators on Kickstarter

A couple of engineer/designers named Dave have a Kickstarter project to fund production of "Coffee Joulies," a little gizmo that brings your coffee down to the optimal temperature and keeps it there.

One of my big beefs with many of the Kickstarter projects I see is that their originators don't give any indication of their ability to see a project (any project!) through to completion. I want to know that my money goes to people who have at least some track-record of finishing what they start. So I wrote to the Daves for more background on their own work and project history and they obligingly sent along a link with some background that makes it clear that while this might be more ambitious than anything they've done to date, they certainly have made stuff happen in the past (Dave P adds, "We have firm quotes from a manufacturer (the one that usually makes Oneida flatware) and a pretty firm development timeline of 12-16 weeks before we can fulfill our orders from Kickstarter."

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.

This amazing feat of thermodynamics happens thanks to a special non-toxic material sealed within the polished stainless steel shell. This material is designed to melt at 140 degrees Fahrenheit, and absorbs a lot of energy as it melts. This is how Joulies cool your coffee down three times faster than normal. Once it reaches this temperature, the special material begins to solidify again, releasing the energy it stored when it melted. This is how Joulies keep your coffee warm twice as long.

Coffee Joulies - your coffee, just right (via Red Ferret)


  1. This is definitely pretty smart.

    The one thing I’m surprised at is the form factor: they went with individual coffee beans that go into your drink, instead of filling the walls of a regular stainless travel mug with this material. I’d love to hear why they did this.

    As I see it, a coffee mug format would have several obvious advantages: no need for extra doohickies to remember to bring — just bring your mug, no wasted space when you use several, existing manufacturing process for creating mugs (and maybe even being able to slip this into an existing mug design), and possibly the ability to use more inner material for less steel used (not sure which material is more expensive in this case).

    Yes, you wouldn’t be able to customize how many you put it, but as far as I can see, there’s no such thing as too many (apparent from the wasted space) — the more of this material you use, the faster you’ll cool your coffee.

    Was the coffee bean format used just because it was cool? (That’s a valid reason.)

    Anyway, this may be my first kickstarter contribution.

    1. I don’t think that “more is better” in this case, because you will not only cool the coffee faster, but also more intensely; the more material you use, the closer the coffee will approach the Joulies’ initial temperature before thermal equilibrium — which will be room temperature. Correct me if I am wrong here.

      Also, the form factor may be because the other approach would have the material facing the outside — losing temperature. This could be countered by using a Thermos container, though…

      Anyway, great idea, great project. I really am tempted to get the enthusiast package, though I don’t drink that many hot beverages to really justify it…

    2. The one thing I’m surprised at is the form factor: they went with individual coffee beans that go into your drink, instead of filling the walls of a regular stainless travel mug with this material. I’d love to hear why they did this.

      Ever own a mug? Ever have a favorite mug? Why should someone give up their favorite container for a a doodad that is only appropriate for one type of beverage?

    3. “The one thing I’m surprised at is the form factor: they went with individual coffee beans that go into your drink, instead of filling the walls of a regular stainless travel mug with this material. I’d love to hear why they did this.”

      they’re relying on the travel mug to provide the thermal insulation from the environment… had they filled the gap between the walls in a stainless steel double walled mug, then half the energy would be going out to the environment, and the coffe would still cool down too fast as there wouldn’t be any insulation anymore either as there’s no airgap….

  2. Definitely very interesting. But how does this not result in some of these ending up in people’s digestive tracts?

    Just askin’.

  3. What if you prefer your coffee at 135 or 145 degrees Fahrenheit?

    This seems to me to be aiming at a vanishingly small market – people who care enough about coffee temperature to want a precise temperature and for whom that desired temperature is exactly 140 degrees.

    If all you’re after is a stable temperature, there are plenty of solutions out there already.

  4. My only concern would be the stainless steel coating degrading and leaching hexavalent chromium into your coffee. It does not seem to be the same as the stainless we are all used to with current travel mugs.

  5. Another question: does anyone understand why you’d ever want to preheat the joulies? The guy mentions this twice on the kickstarter page as being optional, but as far as I can see, the more you preheat the things at the start, the less energy they’ll absorb from your coffee.

    If it turned out to be necessary ever (the guy mentions optionally doing so if you’re using cream), it would seem to be a drawback — one more thing to have to do before you have your coffee.

    @Shane: they’re about 1.5 Tbsp in size, so I think you’d have to be pretty inattentive to swallow one without noticing. I’d worry more about breaking my teeth if I tipped the cup too far back though!

    1. I didn’t see your second comment before posting.

      If you preheat them you escape the problem of cooling the coffee down too much, while retaining the desired temperature much longer.

      1. “while retaining the desired temperature much longer”
        That is, if you add a larger number of preheated Joulies, of course.

  6. I saw these on another wubsite last night and thought it brilliant.

    to address some of the concerns and/or questions people have.

    Why not a coffee cup for the phase change material? Probably cost for now. I would expect that if these take off it will only be a matter of time.

    Why the form factor? Surface area. You get more with flat ovals than say a sphere or cube (also easier to produce). The coffee bean design is for kicks but the general shape ensures you maximize the effect of the heat transfer.

    And as for preheating; if your coffee isn’t hot enough to melt the material on the inside, because you added cream or you waited a couple of minuets before putting them in or something, you want to maximize the ability of the joulies to keep at the ideal temperature. They essentially are heat sinks and the heat transfer equations usually go like: (Tfinal-Tinitial)*someConstant. However when you deal with phase changes you do: (Tphase-Tinitial)*someConstant1+phaseChangeEnergy+(Tfinal-Tphase)*someConstant2 where Tphase is the phase change temprature and the constants are the heat transfer constants for the different phases. Basically you will still be on the phase change temp until the whole of the materials changes phase which takes X amount of energy. Preheating them for cooler coffee would mean you could be 80% or so through a phase change verses 20%. This mean it would keep the coffee at their magic temp longer because more energy is stored in the phase change rather than losing it just getting the joulies up to the phase change teprature.

    As for the degrading outer shell, thats my only concern. But I’ve had a stainless coffee mug for years and I don’t have a whole in the bottom. So it’s probably fine*.

    *I’m not a metallurgist.

  7. One more consideration: A coffee mug with this material in it — how microwave-safe would it be? Dishwasher-safe?

  8. Wouldn’t a solid piece of stainless essentially produce the same results? Don’t know, just curious.

  9. I think the biggest reason for not making these into a mug is, as has been stated, a cost thing, on top of a thermodynamics issue of the material then being more exposed to room temperature and thus losing heat faster. Also, being things you add yourself makes them more versatile–I can still keep my Aperture Science mug and use these things at the time. (Let’s be honest, most people who drink coffee regularly have a favorite mug they use.)

    It’s a really brilliant idea. I don’t know about the 140F temp as being ideal (never checked it myself), but I love the concept.

    Really tempted to invest in this, although being short on cash, $50 seems like a lot.

  10. It they could tweak their material to melt at 152F or so, they could sell it to homebrewers.

    Or at closer to 100F for koji.

    wait, wait – here’s my new plan – a bunch of joulies in a 2 gallon coleman cooler filled with hot water, to make an uber cheap sous vide cooker! I think 140F is actually about perfect for that.

    1. whoops. Just did the math – one joulie is supposed to be good for 5 ounces of coffee, so for a one gallon sous vide setup, I’d be looking at something like 25 beans, and the beans come in at something like 7 dollars each, so that’s out of the uber cheap range.

      It would be pretty cool to see if you could sous vide an egg with nothing more than a well insulated coffee cup and a pack of joulies though.

    2. That would actually be a more expensive way to make a sous vide cooker. If you make a couple holes and fill the lid of a plastic insulated cooler with that expanding, hardening foam they sell at hardware stores (I think one of the brands is Great Stuff or something like that), you can hold your temperature loss to about a degree (or less!) an hour, which is more than sufficient for sous vide provided you check on it every hour or so and give it small spikes of hot water. You can also

      Also, to the Anon at #12: The reason incorporating a phase change is desirable has to do with a concept called latent heat. Basically, in order to get a material to change phase, you have to add some energy above and beyond the energy you would have to add to change the temperature by some amount.

      For instance, water has a certain capacity for heat, which you can use to calculate how much energy it takes to raise a fixed amount of water by a degree. Now, imagine you had a way to deliver a specific amount of heat to a sample, and you wanted to raise it from 99 to 101 degrees celsius , boiling the water in the process (for the sake of simplicity, assume water and steam have the same heat capacity). If you didn’t take phase change into account, you not only wouldn’t raise it to 101 degrees, you probably wouldn’t even manage to boil the water.

      That’s because the phase change itself takes energy, and it can take a LOT of energy. Take a look at the graph on this page, and notice the very wide horizontal section between liquid water and steam:

      You can see by that graph that if you add energy at a constant rate, it takes LONGER to make 100C water boil than it does to take 0C water to 100C. (HUGE CAVEAT: I haven’t done the math on this, so I’m assuming that graph is correct and to scale. But the general idea of it is right).

      So, back to the coffee bean things. By incorporating a phase change into the design, the device can absorb a lot more heat than if the material’s phase change was above or below the range of the coffee’s temperature.

      1. Whoops, I messed up. The following sentence:
        “You can see by that graph that if you add energy at a constant rate, it takes LONGER to make 100C water boil than it does to take 0C water to 100C.”

        would be more accurately rephrased as:

        “You can see by that graph that if you add energy at a constant rate, it takes LONGER to make 100C water raise to 101C than it does to take 0C water to 100C.”

        Also I’d like to add this is an oversimplification of the issue, the chemistry of what’s happening is more complex (and beyond my powers of explanation). But this should suffice for the current topic.

  11. Durned Amazon Payments system does not work with Canuckian addresses. I was hoping to nab a pack of these. Guess not.

  12. Hey Cory, I’ve noticed (from reading your books and posts) that you really like the word “clever” and use it extremely often.

    What’s the deal with that? Is it just something that you use a lot or is it something that’s common where you’ve lived at some point?

    I’m not attacking or trolling; I’m genuinely curious.

  13. joe:

    in fact… its crap.
    a proper made cappuccino (at least thats whats shown in the clip) is drinkable in a few minutes… if its not, you got dead milk.
    a good barista should know that fresh milk shouldnt be overheated..
    slightly under 60degrees celsius..132 fahrenheit..
    am i wrong?!

    1. Oh please. You’ve never spent more than five minutes on a cup of coffee? And what the hell is “dead milk?” Can you explain what is actually happening inside the milk to make it “dead?” I challenge you to take a cup of milk, heat it to 132º, and keep it at 132º for five minutes, and then drink it along side a cup that you’ve only just heated up to 132º. Do you think you’d actually be able to tell the difference, or is this just something you’ve heard somewhere?

  14. Gee, I wonder if their ‘proprietary phase change material’ is just the standard supersaturated sodium acetate solution used in reusable instant heat pads? Certainly the mechanism of action, the melting point and the non-toxicity match up.

    That said, the form-factor is novel, and you probably wouldn’t want to cram one of those cheap reusable instant heat pads into your mug.

  15. This would be really awesome for the elderly. My mother used to work in a nursing home and lots of residents loved to have their own constant access to coffee rather than having to have it dispensed through a cafeteria worker or other staff member and monitored to make sure it was cool before they could drink it. But unfettered access to coffee lead to lots of injury risk. Sure, as a young healthy person, spilling fresh out of the pot hot coffee on myself is lousy, but I’m physically and mentally able to quickly rid myself of the hot coffee before I can be really burned by it, and my skin is in good enough condition that the quick exposure to the heat’s no biggie, a little uncomfy, but not a real injury. For the already fragile and slower moving elderly, a coffee burn can be really painful. The nursing home my mother worked at struggled with the coffee issue constantly, wanting to respect the residents’ dignity by keeping the coffee flowing freely but needing to protect the residents from burns (both for their safety and from a legal liability standpoint). This device would be a super easy fix.

  16. A couple of years ago I saw a TV report here in Germany of guy who designed (already had a working prototype) a coffee mug using the exact same principle. I smell a patent war.

  17. major major choking hazard…
    i would worry that a kid would grab one and toss it in their mouth…no hole in it like a life saver for air…….


  18. I’d only add that while it’s apparently pretty simple to get a Kickstarter project approved for something like eating ridiculous amounts of food while video recording it, or taking pics of women in public who are wearing red shoes, I tried to get a project started for a simplified water well drilling process for remote, rural, and financially restricted locations and was denied. Kickstarter is about what looks cool, not about what helps people.

    1. I think it really depends on how much time you spend sending the info out to relevant blogs, marketing, social networking, etc. I don’t think you can just put a project on Kickstarter and expect it to start raking in the dollars, no matter how good the premise is.

      These guys clearly contacted all the big tech blogs first (gizmodo, etc), who sucked it up because it is not only geeky and techy, but also about coffee, which is what powers the wheels of geeks and techies everywhere. And then once it starts hitting the big blogs, it goes viral.

  19. Sealed stainless steel containers filled with something like Field’s metal…Brilliant!

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