While a cup of green tea may have around 40 milligrams of caffeine, a cup of decaf green tea may have only up to 10 milligrams of caffeine. Decaf green tea has undergone an additional process which removes nearly all of the caffeine naturally present in the green tea. Some decaffeination processes use a solvent, ethyl acetate, while others use carbon dioxide and water.
The carbon dioxide and water process results in a decaf green tea that retains a higher proportion of antioxidants, up to 95% of the powerful disease-fighting catechin EGCG. The ethyl acetate process may retain only about 30% of green tea's EGCG. Check the label or contact the manufacturer to find out about the caffeine removal process used to produce your decaf green tea.