Later On

A blog written for those whose interests more or less match mine.

Trying new things in general—and, specifically, the Joeveo Temperfect coffee mug

with 3 comments

I am what psychologists call “novelty-seeking,” a person who enjoys trying new things. Not all new things, of course. I don’t find competitive sports of much interest in general, though there are some exceptions. But new foods, new books, new gadgets, new ideas—all those things draw me in.

So some years back I was fascinated by a Kickstarter proposal: a triple-walled travel mug for hot coffee or tea, which had a substance contained within the inner pair of walls that melted (and thus absorbed heat) when the hot beverage filled the cup and then slowly solidified (thus releasing heat). The result was that coffee (or tea), initially at a temperature too hot to drink, immediately dropped to a comfortable drinking temperature and then stayed there for a long time.

The ingenuity was attractive, and I kept my eye on it. As seems to happen fairly often with Kickstarter (and I’m thinking of the two Rockwell razors), the innovation turns out to be more difficult in practice than first realized, and it took several years to get things right. But the Joeveo Temperfect mug did indeed finally come to market, and I bought one for The Wife, who regularly buys a good coffee on the weekend to enjoy by the ocean. I bought this one.

It turned out not to be her cup of tea, as it were. First, it’s a 16-oz mug, and she prefers a 12-oz coffee. Second, and more important, it’s heavy. It has three stainless-steel walls, the outer two of which enclose a vacuum, and a third wall that, with the internal vacuum wall, encloses the magic substance.  Empty, it weighs a pound—actually, 1 lb 2 oz. Filled with 16 oz of coffee, it’s just over two pounds. For me, that’s fine, given what it does. For The Wife, it’s too heavy.

Here are the details:

The Temperfect mug has three stainless steel walls (alloy 304L, cutlery grade), and two layers of insulation. On the outside is a vacuum insulation layer which ensures no heat is lost. On the inside, a layer of Temperfect insulation absorbs the excess heat from your beverage, stores it, and slowly puts it back into your drink to prevent cooling. This cycle can be repeated forever, so it will never wear out.

The Temperfect insulation is a phase-change material (PCM), a non-toxic, wax-like substance which changes from solid to liquid phase as it absorbs heat, and from liquid back to solid as that heat is used to keep your drink at a perfect temperature.

There are two aspects of the physical process of phase change that make it perfect for this application.

  1. The change occurs at a constant temperature (if the PCM is pure and has a single crystalline phase.) This property is what keeps your beverage at a constant temperature.
  2. A large amount of energy must be transferred either to or from the PCM to change its phase. This is what enables it to store energy to keep your drink at just the right temperature for a long time.

Here are actual measured temperatures for a typical vacuum-insulated mug (think Thermos, Stanley, Contigo, Yeti…), for a basic ceramic mug, and for the Temperfect mug:

It’s getting its first use now. The initial sip is fine: the coffee is at a drinkable temperature and doesn’t require the cautious blowing that a take-out coffee usually requires before the first sip. Now that I have brought it home and had it sitting beside my chair, it’s still the same temperature, which seems hot because I unconsciously expect it to have cooled. It’s still easily drinkable without burning, and it’s also still the same temperature as when I tasted it on the drive home. In a word, it works.

An important note: Temperfect brings brewed coffee (which generally has a temperature of around 160ºF) to drinking/sipping temperature quickly, and the holds it there for hours. BUT if you pour a pint of boiling water (temperature of 212ºF) into the mug and stir in a tablespoon of instant coffee, then (as you’ll quickly discover), the coffee is still much too hot.

The reason is obvious: the mug is designed to cool a pint of 160ºF liquid to drinking temperature, and it simply can’t absorb enough heat from a 212ºF liquid to make it cool enough to drink. So when I make instant coffee in the mug, iI add two ice cubes after the instant coffee has been added and dissolved. That brings the temperature down, and then the Temperfect mug holds the liquid at that temperature for hours.

With hot tea, the problem is avoided because (a) the teapot itself absorbs some heat from the boiling water; and (b) the tea steeps for 4 minutes, which cools it further. Thus the tea is substantially below boiling temperature (212ºF) by the time I pour it into the Temperfect. Even so, I have to be cautious for the first few sips, but the tea is quickly at drinking temperature — and there it remains, for hours.

But note a second problem with pouring boiling water directly into the mug: These mugs have enough energy absorption capacity to bring boiling water down 17°C (if they are initially at room temperature), so if you’re starting with 98° or so, it’ll probably still be too hot for most. The higher the temperatures the lid is exposed to, the more it will be sensitive to the mechanical stresses of tightening that will cause it to become warped. The result is that after repeating this stress daily, the lid will not tighten well. Moral: The Temperfect mug was designed for brewed coffee (at around 160ºF), not for boiling water. Don’t use boiling water any it.

I’m not really a coffee drinker any more, but I definitely will try it with tea. It’s rather tall, but the steady temperature may compensate for the extra height. I really hate it when my cup of tea cools off, and that makes me drink it fast, so that instead of enjoying the cup of tea while I read, the cup is empty before I’m barely started. This may fix that.

Update: Yep, this is my new tea mug. I really like sitting back in my chair with a good book and a cup of tea for a leisurely read, but because of the speed with which a regular mug of tea cools, I empty the cup within the first 10 minutes, so the idea of leisurely reading and sipping was out the window. And though iced tea is nice, it’s surprising how quickly the ice melts and must be refreshed.

I’ve been reading now for a couple of hours, taking a sip of tea every now and then. There’s still quite a bit left in the mug, and it’s still at a perfect temperature for drinking. I think this is going to displace iced tea for me—or, more likely, move iced tea to the afternoon, and in the morning cup drinking a mug hot tea (all morning long!).

Update again: When I sit down with my computer in the morning to peruse the news, read my email, and so on, I often get involved and forget I brought in a cup of tea, so that when I remember the tea is already cold and I’ve not had a sip. This morning I once more plunged down a rabbit hole in researching an answer on Quora, and when I suddenly recalled that I had some tea, it was still at the perfect temperature. Little things make me happy. 🙂

Written by Leisureguy

4 May 2019 at 8:22 am

3 Responses

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  1. Thanks for the review Leisureguy! I’d love to offer a 12 oz desk version, but I need to build up some resources before taking on a new project of that magnitude. After following the Kickstarter, you know what is involved 😬 –dean



    6 May 2019 at 7:01 am

  2. The 12-oz size is purely The Wife’s choice. I’ve always preferred a pint, and my regular tea mug (the one that cooled too quickly) was a Starbuck’s 16-oz mug. Even as I type this, I have a my Temperfect mug beside my chair, sipping tea from it. It’s been an hour, and the tea is still at the perfect temperature.

    No rush for me on the 12-oz size. I like what you have now.



    6 May 2019 at 7:04 am

  3. My own go-to is a 12 oz, so I understand your wife’s preference.



    6 May 2019 at 7:18 am

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