Magnézium Szulfát, keserű só(Epsom só) MgSO4 25g

Lowers pH slightly. 

Magnesium sulfate is similar to calcium sulfate but is not as effective as calcium in reducing the pH of the mash.

Can be used to add sulfate "crispness" to the hop bitterness. Use sparingly as too much can have a laxative effect!

Magnesium (Mg)
Magnesium is a critical yeast nutrient if used in small amounts. It also behaves as calcium in contributing to water hardness, but this is a secondary role. Levels in the 10-30 mg/l range are desirable, primarily to aid yeast. Levels above 30 mg/l will give a dry, astringent or sour bitter taste to the beer.

Sulfate (SO4)
Sulfate plays a major role in bringing out hop bitterness and adds a dry, sharp, hoppy profile to well hopped beers. It also plays a secondary role to lowering Ph of the mash, but the effect is much less than with carbonates as sulfate is only weakly alkaline. High levels of sulfate will create an astringent profile that is not desirable. Normal levels are 10-50 mg/l for pilsners and light beers and 30-70mg for most ales. Levels from 100-130 mg/l are used in Vienna and Dortmunder styles to enhance bitterness, and Burton on Trent pale ales use concentrations as high as 500 mg/l.