This traditional ume concentrate, known as bainiku ekisu (plum extract), was developed in Japan a few hundred years ago to concentrate the healing properties of ume. Sour green ume plums are slowly cooked down to obtain their most active ingredients in a highly concentrated form. The resulting dark, sticky, thick liquid is usually mixed with hot water and honey and drunk as a tonic. The citric acid content of the plums is concentrated tenfold, which is equivalent to about twenty-five times the content found in lemon juice.