Magnesium Sulphate (MgSO4), commonly known as Epsom Salts, is typically the secondary ion in hardness in water.
Magnesium, like calcium, will help to reduce mash pH, however it is not as effective in lowering pH as calcium.
It accentuates flavour with a sour bitterness, when present in low concentrations and can be used very effectively in pale ales and IPA's.
Magnesium is also an important yeast nutrient aiding in flocculation, however sufficient magnesium should be supplied by the malt during the mash. As such it should only be added to brewing water for its flavour effects.
Before adding salts to your brewing water you should obtain a water analysis report to enable you to calculate the amount of salts in your brewing water after making any additions. Refer to theBrewing Resourcespage for some links to water chemistry calculators.
Clickhereto read the Bru'n Water Water Knowledge page, which contains everything you need to know about brewing water.