Chemistry Of A “Therm au Rouge”

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This may be the wrong sort of blog on which to ask this, but…

Our family has a “Therm au Rouge” (that site has the best images) wine-warming sleeve – one of those things you buy for a Christmas present out of desperation. It wraps round a bottle of wine and, after “clicking” a small square of metal inside the pouch by bending it, an exothermic reation is initiated which warms the wine. The reaction spreads out from the “clicker” and the clear liquid in the sleeve turns into a white solid, emitting heat in the process.

The reaction is reversible; when it’s complete, you can boil the pouch in water for ten minutes to reverse it and turn the liquid back to clear. The instructions say it’ll work at least 100 times before you should replace it.

I’ve searched the web but I can’t find out:

  1. What is the chemical reaction involved?
  2. How does the clicker which initiates it work?

Our family is having a Christmas “discussion” about this so if anyone has any ideas, I’d love to hear them…

7 thoughts on “Chemistry Of A “Therm au Rouge””

  1. Just a wild guess… maybe it’s actually some sort of rechargeable battery and the metal thing short circuits it?

  2. I asked my friend Darren and he replied this:

    ===================================
    Hi iang

    The phenomenon exploits something called the “heat of crystallisation” …

    When things crystallise the process can be either exothermic (gives out heat) or endothermic (takes in heat).

    The “jacket” has something in it that gives out heat when it crystallises; for these items, the something, is often a saturated solution of sodium acetate.

    Note, I used the word ‘saturated’. For, crystals to form a ‘seed’ is usually required. If you go into a lab and a chemist is trying to crystalise a new compound, you might see him scratching the side of his test tube with a glass rod. He’s trying to create a seed (of glass) that allows other crystals to form from the solution. This is what happens with the “clicking” that you describe. The “clicking” shocks the saturated system and crystals form giving out heat. After the heat has gone you can put the belt into a warm oven; this melts the crystals and upon cooling – if there is no initiation (clicking) the crystals will retain the heat. When the heat of crystallisation is required … click again.

    As a further bonus … another example of something that is dissolved in something in a supersaturated manner is the carbon dioxide in your carefully opened bottle of beer. If you tap the edge of the bottle – hard but not hard enough to break the glass – the carbon dioxide will cascade out of your beer. The ‘tapping’ is equivalent to the ‘clicking’.

    Merry Christmas, iang … any of my spelling mistakes are to be blamed on my lager.

    Darren.

  4. Gerv, these explanations about sodium acetate, supercooling, etc., are all well and good, but there’s a more serious question left unanswered: Why do you want to *warm* wine? Is this an English thing? :-)

  5. Also there are other extremely supercooling liquids but just not as cheap and/or safe as NaAc

  6. Guys: that’s fabulous; thanks very much for all the explanations. My family is now enlightened, and I got to appear wise ;-)

    Frank: white wine should be served chilled, and red wine at room temperature, as I’m sure you know. However, many places one might store wine are colder than room temperature. Hence, one often puts the bottle in front of the fire or on a radiator to warm up before drinking it. However, if one forgets, this gadget comes to the rescue.