Coffee Joulies: A Review


Coffee Joulies

If you were to draw a Venn diagram of coffee aficionados and tech geeks, Coffee Joulies would be in the intersection of the two sets.

{Hang on to your hats here, as we will be transitioning from Venn diagrams to physics textbooks, thermal energy and the properties of phase change materials shortly.}


Coffee Joulies: The Product

Coffee Joulies are stainless steel “beans” filled with a plant-derived phase change material that melts at 140 °F. The concept behind the product is that the Joulies will absorb thermal energy (melting the material sealed inside), bringing the temperature of the surrounding coffee to “the perfect drinking temperature.” As the coffee continues to cool, the Joulies will then release that stored thermal energy (re-solidifying the material sealed inside) to the surrounding coffee, “keeping it in the right temperature range twice as long.

The net effect (in theory, we will get to practice in a bit) is that your coffee reaches ideal drinking temperature sooner and stays there longer.

The full tech specs from the creators of the product, Dave & Dave (via the Coffee Joulies Kickstarter project page):

  • Shell Material: Polished Food-Grade 18/10 Stainless Steel
  • Inner Material: Proprietary Phase Change Material (PCM), melting point 140°F
  • Displacement: 0.75 oz (1.5 Tbsp) per bean
  • Coffee Volume Per Bean: 5 oz including bean (4.25 oz without bean)
  • Coffee Volume Reduction: 15%
  • The “Right” Temperature Range: 140°F to 130°F

The Coffee Joulies website also states that the seal of each Joulie is tested with a helium leak tester: “the same technology NASA uses to test parts used on the space shuttle.”

The product is available in the Coffee Joulies 5-pack, for $49.95.


The Buzz

Coffee Joulies launched as a Kickstarter project, which automatically gives them a certain amount of indie cred in my book.

There is also a bit of a tech/gadget geek inside of me, and I was impressed by the press the Coffee Joulies launch received in that realm: Wired? Check. Uncrate? Check. SlashGear? Check. Boing Boing? Double check (here and here).

This initial enthusiasm was kept in check by a healthy dose of skepticism. Do they work?

And even if they do work as advertised, aren’t they a bit of a unitasker? I have to give Unclutterer credit for instilling in me a strong aversion to unitaskers in the kitchen. (See here for my favorite coffee-related unitasker review.)

So with Joulies in hand, I entered the product testing phase with my initial impressions score tied 1:1.


Coffee Joulies

Our Experience

The “in hand” experience was the first surprise. Coffee Joulies are both larger and lighter than I expected—the FAQ page describes them as “about the size (and shape) of half a medium chicken egg.”

As I move from hand to cup, I want to make this disclosure: I prefer my coffee on the hotter side and my cup on the smaller side.

A single Joulie takes up some considerable real estate in my favorite medium-size cup (approximately an 8 ounce cup, give or take). As the recommendation is one Joulie per 4 ounces of coffee, I conducted my review using two Joulies.

Note: The manufacturers states you will achieve best results with a vacuum insulated travel mug, and they offer a kit with their branded travel mug for $79.95. As I couldn’t parse how I would possibly (without extended and laborious experimental trials) separate the effects of the Joulies from the effects of the vacuum insulated mug, I decided for the purposes of this review to stick with my favorite mug.

I tested the product over the course of three days, at home and at coffee shops.


Test Results

In terms of pure convenience, I didn’t enjoy having to wash and dry the Joulies before returning them to my bag when I was out and about.

In terms of performance, I am going to give a thumbs-down, with some caveats. Again, I like my coffee on the hotter side. I didn’t feel that the Joulies maintained the temperature of my coffee within my ideal range. Your mileage may vary. If you are on that slightly cooler end of the spectrum, Joulies may be the tool for you. I also did not notice any appreciable difference in how long my coffee stayed at this temperature.

My mind kept returning to the manufacturer’s statement that 140 °F is “the perfect drinking temperature.” If you read our recent post on buying coffee beans online, you might remember a reference to the Specialty Coffee Association of America Cupping Protocols. The SCAA recommendation for the ideal temperature for evaluating flavor, aftertaste, acidity, body and balance of coffee is 160 °F to 140 °F.

That “perfect drinking temperature” is at the low end of the SCAA range. Additionally, the technical specifications listed on the product’s Kickstarter page reference a temperature range of 130°F to 140°F.

Returning to that intersection where coffee aficionados and tech geeks meet: We have graphs! Marco Arment, “creator of Instapaper, technology writer, and coffee enthusiast” shared experimental results in his review of Coffee Joulies, noting that he was not using lab-precision equipment under lab conditions and that his measurements should be considered approximations. The temperature charts he presents do not demonstrate an appreciable insulative effect from the Joulies. Arment concluded: “While Joulies may help a bit, they’re probably not worth their cost to do so.”

In rebuttal, the manufacturer posted a detailed comment on Boing Boing’s review of Arment’s review, stating: “We have run our own tests in literally dozens of scenarios, and the performance varies from greatly exceeding our claims to situations like Marcos.” They further noted that Arment’s review did teach them “a ton about managing expectations and about the learning curve associated with our product.”


Our Awards

I consider my expectations well managed at this point, and my position on the learning curve adequately well advanced. From this position, I’m going to have to pass on Coffee Joulies in my personal coffee repertoire.

That said, CoffeeKrave still has some Joulie-related accolades to hand out.

Our nominee for best review title: Jeff Ammons’ post (also a review featuring experimental results with graphs): “A Swift Kick in the Joulies.”

And our nominee for best product related blog comment: kernkraftworks (via the Boing Boing page): “. . . 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.”

Do you have this product and consider them the Crown Joulies of your mug? We welcome all points of view in the comments below!


Main photo and Content photo via the Coffee Joulies Kickstarter project page.


Robyn is a freelance writer, editor and a serious foodie. A native of Seattle, she has found a new home in Northern California where she splits her time about equally between hiking in the redwoods and typing in local coffee shops. In addition to writing for CoffeeKrave, Robyn is currently working on a project to produce a short animated documentary—"Clipped and Tucked"—about her adventures in cooking recipes from antique cookbooks.

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