Effect of different brewing times on soluble oxalate content of loose-packed black teas and tea bags.

Abstract

Because of the postulated role of increased dietary oxalate intake in calcium oxalate stone formation, the effect of different brewing times on soluble oxalate contents of loose-packed black tea and tea bags was studied. The oxalate content of 25 different samples of loose-packed black teas after brewing at 5, 10, 15, 30, and 60آ min and of ten brands of tea bags after infusion for 1, 2, 3, 4, and 5آ min was measured by enzymatic assay. The oxalate concentration resulting from different brewing times ranged from 4.3 to 6.2آ mg/240آ ml for loose-packed black teas and from 2.7 to 4.8آ mg/240آ ml for tea bags. There was a stepwise increase in oxalate concentration associated with increased brewing times.