Effect of calcium and sodium ions on coffee proteins and foam.

The brew is prepared by decoction in a graduated cylinder with demineralize d water containing CaCl2 or Nacl (between 0 and similar to0.1 M) and 10 % ( w/v) of ground coffee. Ca++ decreases the solubility of proteins (PR) of co ffee and its foaming power (PM) but increases foam stability ISM), probably by gel formation. Addition of Ca++ is also accompanied by a decrease of pH . Na+ has no significant effect (p > 0.05) on PR, PM, SM or pH. The measure ment of electrical conductance shows that the two ions are partially immobi lized by one and/or the other component of the brew.