Kwatha Kalpana or Kashaya as is popularly known, is amongst the most used ayurvedic potions and treatment methodologies. In fact, Kashaya is one amongst the five kalpanas of ayurvedic medicine, the other four being Swarasa (Fresh juice), Kalka (Herbal paste), Hima (Cold water infusion), and Phant (Hot water infusion).The origin of the word Kwatha is from its root, ‘kwathate’ meaning to boil or prepare by heating.
Different acharyas of ayurvedic medicine, viz.. Sharangadhara, Vagbhata and Sushruta, have explained different methods for preparing kashaya from various herbs, but the basic methodology remains the same. It is basically a simple method wherein the herb is added to water and reduced till all the essence of the herb is captured and the resulting concoction is used. While Sharangadha advises that water be taken depending upon the nature of herb, charaka advises that cow’s urine be added during preparation for its exquisite medicinal properties. Sushruta meanwhile proposes that the herb be dried before commencement of preparation. According to Harita, kwatha is classified based on the quantum of heating used. In most cases, the agni is mridu-agni, or moderate fire, which is less than 100 degree C.
Most of the kashayas marketed in ayurvedic medicine are made in bulk quantities by reduction upto 1/8th part and do not have a very high shelf life. A bottle of kashaya, once opened, needs to be finished and is not advised to be stored for a long duration. Leading ayurvedic hospitals in Kerala make their own kashayas and hence for better shelf life, even some safe and permissible preservatives are added.