The impact of Ca2+ combination with organic acids on green tea infusions

The effect of Ca2+ in brewing water on the organic acid content, turbidity, and formation of tea cream and sediment in green tea infusions was studied. When the Ca2+ concentration of the brewing water was >40 mg L−1, the green tea infusion became more turbid. The turbidity of the tea infusion was highly negatively correlated with the contents of oxalic acid (R = −0.89, p < 0.01), quinic acid (R = −0.90, p < 0.01) and tartaric acid (R = −0.82, p < 0.01). Oxalic acid on its own interacted with Ca2+ at low concentrations, whereas polyphenols and protein did not. In conclusion, Ca2+ in brewing water influences the quality of a tea infusion by inducing tea cream and sediment formation from combination of Ca2+ and organic acids, such as oxalic acid, quinic acid and tartaric acid. Ca2+ and oxalate are the main metal ion and anion, respectively, involved in tea cream and sediment formation on tea infusion cooling or concentrating.