A brewing puzzle

Warning: this post is not about programming.  Andy suggested I should sneak some homebrewing material onto my blog, and I thought hmm, why not?  If you violently object, let me know in the comments and I won’t do it again 🙂

Yesterday I brewed a traditional German hefeweizen, which was the first time I tried a decoction mash.  This got me thinking about how incredibly accurate traditional brewers managed to be, long before the arrival of chemistry, biology, or scientific measuring tools.  This particular trick might be obvious to people with a stronger background in physics, but I thought it was pretty amazing.  So, a puzzle…

Hans is a 17th century German brewer.  He wants to attract a loyal customer base who will seek out his beer in preference to that of competitors.  To achieve this, he must:

  1. Make beer that people like to drink
  2. Make it the same way every time, so customers come to trust the quality of his product

One of the key steps in brewing is heating a mix of water and crushed malted barley (called the "mash") to 152 °F, where amylase enzymes will convert starch molecules into sugars that yeast can later ferment into alcohol.  But Hans does not have access to a thermometer, so he has no way to accurately hit the right temperature.  He can estimate by sticking his finger in the mash, but even with lots of practice this is horribly inaccurate.  Sometimes he ends up at 148 °F, which produces a dry, thin beer.  Other days he ends up at 158 °F, which gives a thick, syrupy end result.  One time he overshot all the way to 170 °F, which accidentally denatured the enzymes, leaving him with a couple of tons of watery grain that could no longer be used to make beer at all!

Is it possible to do better?  How can Hans heat his mash to exactly 152 °F without the use of a thermometer?

Comments (7)

  1. Clayton says:

    This is probably going about it the wrong way, but I don't suppose the answer has anything to do with Methanol's boiling point of 151F (at one atmosphere).

    152F happens to be 2/3 of the way between 0C and 100C, so Hans could mix 2 parts just-boiled water with 1 part just-frozen… and uh, somehow keep it at that temperature.

    I really know nothing about brewing.

  2. desadoc says:

    Maybe if he could keep a constant heat supply, the mix would eventually reach an equilibrium where it irradiates and transmits the same energy it receives. A stronger heat source would raise the temperature.

  3. Tony Yates says:

    Alternatively, you build a HERMs system like I have. 😉 From TheElectricBrewery.com

  4. mantis says:

    (It's easier for me to think in Celsius about these). 152 K is 66.(6) Celsius. At 100 degrees C water boils, at 0 it freezes. Take 2 parts boiling water, 1 part freezing, and compare the temperature to that of the brew?

  5. dgschrei says:

    Since water like all other substances expands when you heat it, and you said it had to do with physics, I'm assuming you have two marked lines on the boiler.

    The first one is the mark to which you have to fill the boiler, the second one is the line to which the water will have expanded when it hits 152° F. Once the water reaches that line you know you have the right temperature.

    I'm just not sure how accurate that would be. Water in it's liquid form really doesn't expand all that much.

  6. Weight the mixture, lets say 10 kilos, take 3.3 kilos of water and heat it until they boil, return to the mixture and remove… make sure the pot is well isolated so heat doesnt scape.

  7. BlueRaja says:

    mantis has it, with two caveats:  1. Make sure you go by *mass*, not *volume* (water expands when freezing, so the same volume of ice will have lower mass), and 2. You have to make sure the water is just *barely* freezing (it's not possible for water to be over 100° C, but it *is* possible for it to be below 0° C)

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