Lesson 5 - Brewing Water Composition and Impact SAQ
This lesson provides the opportunity for you to test yourself on the material covered in Lesson 4 (Brewing Water Composition and Impact) and determine the level to which you have attained the expected outcomes.
Suggested Response - Q2
**The mineral content of the base product water in your brewery is as follows:
Calcium – 30 mg/L
Sulphate – 50 mg/L
Chloride – 50 mg/L
mw of Ca is 40
mw of SO4 is 96
mw of Cl2 is 71
mw of H2O is 18
a) You would like to brew an amber lager. How would you adjust the mineral levels? Show any calculations.
b) If you added 104 mg/L of calcium sulphate (CaSO4.2H2O), what beer style/s could you brew?
Response:
a) An amber lager should ideally have a higher level of calcium. Although the levels of chloride and sulphate are fine, the ratio is wrong. The ratio of chloride:sulphate should be 2:1 to support the malt flavours of the amber lager. Therefore, the calcium and chloride levels should be increased and thus, calcium chloride needs to be added.
If the target addition for chloride is 50 mg/L, then:
The chemical formula for calcium chloride is CaCl2.2H2O, so calcium chloride has a molecular weight (mw) of 147. The chloride part of the calcium chloride molecule has a mw of 2 x 35.5 = 71.
This means that for every 147 mg of CaCl2.2H2O added, we get 71 mg of Cl in solution.
The calculation for required calcium chloride addition is then:
Required CaCl2.2H2O = mg of Cl required x (mw CaCl2.2H2O / mw of Cl2 )
Therefore:
Required CaCl2.2H2O = 50 x (147/71)
Required CaCl2.2H2O = 50 x 2.07
Required CaCl2.2H2O = 103.5 mg/L
Amount of Ca added = amount of CaCl2.2H2O added x (mw Ca / mw CaCl2.2H2O)
Therefore, the amount of calcium added is:
Amount of Ca added = 103.5 x (40/147)
Amount of Ca added = 103.5 x 0.27 = 28 mg/L
Therefore, by adding 103.5 mg/L of calcium chloride, you add 50 mg/L of chloride (taking the total amount to 100 mg/L and 28 mg/L of calcium, taking the total calcium levels up to 58 mg/L). This means that the calcium levels are now within the recommended levels of 50-75 mg/L for an amber lager. The chloride levels are in the recommended levels of 50-150, the sulphate levels are already within the recommended levels of 0-100 mg/L. The chloride:sulphate ratio is also now at the recommended 2:1 ratio for an amber lager.
b) The chemical formula for calcium sulphate is CaSO4.2H2O. This has a molecular weight (mw) of 172.
If the amount of calcium sulphate added is 104mg/L, then we can use this calculation to work out how much calcium has been added:
Amount of Ca added = amount of CaSO4.2H2O added x (mw Ca / mw CaSO4.2H2O)
Therefore, the amount of calcium added is:
Amount of Ca added = 104 x (40/172)
Amount of Ca added = 104 x 0.23 = 24 mg/L
Amount of calcium added = 24 mg/L, which takes the total calcium to 54 mg/L.
The amount of sulphate added = amount of CaSO4.2H2O added x (mw SO4 / mw CaSO4.2H2O)
Amount of sulphate added = 104 x (96 / 172)
Amount of sulphate added = 104 x (0.56) = 58 mg/L
Therefore, the amount of sulphate added is 58 mg/L, taking the total sulphate to 108 mg/L.
The mineral composition is now:
Calcium – 54 mg/L
Sulphate – 108 mg/L
Chloride – 50 mg/L
Chloride:sulphate – 1:2