Effect of Water Hardness on the Scum Formed during Soup Stock Preparation

Abstract

The effect of water hardness on the scum formed during soup stock preparation was examined. Three kinds of mineral water were used for preparing the soup stock, in addition to artificial mineral water with various levels of hardness that was prepared by adding calcium sulfate or/and magnesium sulfate. The weight of scum formed with the three kinds of mineral water was statistically heavier than that formed with distilled water, although the weight of scum was not proportional to the water hardness. All samples of artificial mineral water prepared with only calcium sulfate or magnesium sulfate formed statistically heavier scum than distilled water, the weight of the scum formed being proportional to the hardness. However, calcium sulfate caused more scum formation than magnesium sulfate. In the cases of artificial mineral water prepared with mixed calcium and magnesium, the scum formation was suppressed more than in artificial mineral water containing only calcium sulfate. The calcium content in the scum was increased in accordance with that in the mineral water samples used for preparing the soup stock, although there was no substantial difference in the contents of protein and the other minerals.
It was concluded that scum formation was affected by the calcium content of the water, rather than by the water hardness up to about 1,000 hardness, and that an increase in the ratio of the magnesium content suppressed scum formation.