Expert: Alan Ward - 6/17/2006

Question
Remind me again what exactly gypsum does for the brewing water?  Some older recipes say to add gypsum to every batch, but is this necessary or wise?  Thanks, john white.

Answer
The addition of gypsum is used to harden the water and reproduce a water profile. If your using gypsum then most likely you either have very soft water or you are brewing mainly English-Style Pale Ales.

One might think that water is water, but in brewing that is not quite so. The presence of the different minerals in water that make up its relative "hardness" also affect the taste of beers and ales. One of the most well known water profiles is that of Burton-on-Trent, Staffordshire England.

The characteristics of a water source can even influence the development of a classic beer style. One historical example of this process comes to mind. English-Style Pale Ales developed in Burton, an area known for water high in calcium sulfate (gypsum). The high calcium content of the water helps create the body and balance found in this style. The sulfate provides a slight sulfate "bite," and aids the extraction of bitter resins from the hops. Brewers in nearby Yorkshire County later tried to compete against the pale ales produced in high gypsum areas like Burton. The Yorkshire water contains high levels of calcium carbonate (chalk or limestone.) The calcium carbonate tends to add harsh notes to the hops, so beer produced in these areas is light on the hops. Without a strong hop flavor, the brown ales produced in places like Newcastle and Tadcaster have a strong malt flavor and character without excessive hop flavors. Thus, the water characteristics indigenous to a region have influenced the developent of many unique beer styles.


In short the gypsum is used to raise the Ca and SO4 content in the brew water.

You can get a very scientific answer at http://www.rpi.edu/dept/chem-eng/Biotech-Environ/beer/water2.htm .

I hope this helps, if not let me know and I will try and find another way to explain water profiles.  I would suggest getting a copy of your local water profile.  This can be gained usually for free from your water provider or take a sample to a pool store for analysis.

Alan