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I'm brewing from an Austin Homebrew extract kit, and it came with some gypsum. I thought gypsum was only for modifying water chemistry, but there seems to be some other schools of thought around.

So:

  • What does it affect?
  • When/how should it be added?
  • How much should be added?
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3 Answers 3

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Gyspum (CaSO4) does a couple different things. If you add it to the mash, it can lower the pH. The added sulfate content will also accentuate the bitterness of your beer. If you want to increase the sulfate for bitterness enhancement but don't want to change your mash pH, you can add it directly to the kettle. The best way to decide how much to add is to get a water analysis so you know what your baseline is and how much gypsum you might need. You should never add water treatments just because a recipe says so. Know your water, then you'll know if you need them and how much you need.

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    Once you get your water report - 1 gram of gypsum per gallon adds 62 ppm calcium, 147 ppm sulfate
    – Northern Brewer Chris
    Nov 23, 2010 at 21:49
  • Don't forget that calcium is a vital ion required for yeast flocculation. Otherwise, great answer.
    – brewchez
    Nov 23, 2010 at 21:49
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Austin Homebrew's kits are top notch as is their support. I strongly suggest you contact them if you have any questions regarding one of their kits. If they added it, it wasn't done arbitrarily. It may be a particular style of beer may benefit from it, such as a stout.

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    In general, a stout would not benefit from gypsum. It would more likely benefit from CaCO3. And I guess I wouldn't be so sure that it wasn't an arbitrary addition to the kit. How would they know what the brewer's water was like?
    – Denny Conn
    Nov 24, 2010 at 16:15
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Stouts dont need water adjustments, the higher the pH the better - dark malts absorb alkalinity and levels the pH automatically.

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    Not everyone has alkaline water - if I brew a stout I have to add chalk or baking soda to balance the acidity of the roasted malt.
    – mdma
    May 29, 2013 at 16:42
  • That's a pretty broad assumption, and a little inaccurate. Yes, using dark/roasted malts in moderate percentages will bring down the pH (it's estimated that 20% dark crystal or roasted malts will reduce the pH by .5). To say that it levels it is not always true given all the other variables in the equation.
    – Scott
    Jun 5, 2013 at 0:05

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