You need 50 ppm calcium in your brewing water to make good beer. That’s a fact. You can look it up in How To Brew 2, or in Bru’n Water’s Water Knowledge Page1, or even in the book on brewing water 3.

Once you do lookup the fact that you need 50ppm calcium, you may wonder: who proved this? Who made this fact a fact? I haven’t been able to find that answer. Not that I’ve really looked all that hard for the answer, but shouldn’t it be just as easy to find as the fact itself? Oh, OK, W.F. McWhozitz proved the 50ppm calcium thing in 1804 after his expedition to Tanzania…that seems right.

I don’t understand how you can get away not citing sources for stuff like this?

“I mean, if I went ‘round saying I was an emperor, just because some moistened bint had lobbed a scimitar at me, they’d put me away!”
– Dennis

At this point it’s a logical fallacy to even say that the 50 ppm fact is, in fact, factual (see: argument from authority). It’s just another piece of brewing dogma.

Not. Good. Enough.

However, before committing to any kind of full-blown, multi-week, experiment, we first must examine if there is even a reason to doubt that you need 50ppm calcium.

The oft-cited reasons for needing 50ppm calcium in brewing water:

  1. Enzymatic activity in the mash
  2. Yeast health/activity
  3. Protein coagulation in the fermenter

The results of these problems, in practical terms, are, respectively:

  1. Your grain’s starch will not convert to sugar in the mash.
  2. Your beer won’t ferment, or will have significant problems fermenting.
  3. Your final beer will be hazy.

If you could disprove one of those things, maybe it’s worth designing an actual experiment to test the effect of calcium on brewing and the beer it creates.


  • If a mash passes an iodine test, it’s starch has been converted.
  • If a mash made with distilled water passes an iodine test, then calcium from water is not strictly necessary for mashing.


  • 300mL Distilled Water (plus bunches more—see Methods) water 300g

  • 150g Crisp Marris Otter Malt (only base malt on-hand) grain 150g
  • Big MF’n Thermos thing for use as a mash tun
  • iodine
  • Thermopen and lab thermometer
  • White dish on which to test for conversion


I aimed for a mash temperature of 152°F, I did a calculation in Beer Alchemy that showed that the water should be heated to 165°F to achieve a mash temp of 152°F. Then I thought, I’m smarter than you Beer Alchemy and went with a strike temp of 160°F which, ultimately, resulted in a mash temp of 145°F…you win this round Beer Alchemy.

Water temp Mash temp

I then checked for conversion every 15 minutes and made observations about what I saw:

  1. 15 Minutes:

    Iodine test 15mins
    Iodine test 15mins
    • Mash temp: 142°F
    • Iodine test: positive for starch
    • Observations: Smells starchy, a little visible foam indicating CO2 release
  2. 30 Minutes:

    Iodine test 30mins
    Iodine test 30mins
    • Added 60mL boiling water as temp had dropped below 140°F
    • Mash temp: 143°F
    • Iodine test: positive for starch
    • Observations: Thermos thing sucks
  3. 35 Minutes: Added another 75mL boiling water. Temp now 146°F, FML.

  4. 45 Minutes:

    Iodine test 45mins
    Iodine test 45mins
    • Mash Temp: 143°F (Really!? Really mash temp? Fucking, Really!?)
    • Iodine test: positive for starch
    • Observations: I hate this Thermos thing with the power of 1000 suns; I’m gettting better at iodine tests :)
  5. 50 Minutes: Added 100mL boiling water (YOLO!) to raise mash temp to 150°F, YAY!

  6. 60 Minutes:

    Iodine test 45mins
    Iodine test 45mins
    • Mash temp: 146°F
    • Iodine test: negative for starch
    • Observations: Smells and tastes sweet


  1. I am not smarter than Beer Alchemy
  2. While the mash did take a long time to convert, the mash was only solidly in the correct temperature range for alpha-amylase activity for 15 minutes during which time the mash fully converted the remaining starch.
  3. The only solid iodine test, IMO, was the last. The photos tell that story.
  4. Water-derived calcium is likely not strictly necessary for the conversion of starch in the mash.
  5. Actual experiment is in order…
Starting gravity
Starting gravity

  1. Brungard, Martin. “Water Knowledge.” Web.
  2. Palmer, John. “Understanding Mash pH. Reading a water report. Calcium.” How To Brew. Web.
  3. Palmer, John and Colin Kaminski. Water: A Comprehensive Guide for Brewers. pg. 33. Print.