Assam; khar cooking is documented as a uniquely Assamese technique; the Brahmaputra valley's abundance of banana plants made ash lye a natural, readily available cooking medium
Khar (কাৰ) is one of the most unusual cooking mediums in Indian cuisine: a strongly alkaline liquid made by filtering water through the ash of banana plant (Musa paradisiaca) stems or peels, resulting in a potassium hydroxide-rich solution that is used to cook fish, gourd, and lentils in a technique unique to Assam. The alkalinity softens fibrous plant material dramatically (the same principle as using lye in Nordic lutefisk or Japanese ramen's alkaline noodles), imparts a distinctive mineral, slightly soapy-savoury flavour note, and acts as a preservative. The dish 'khar' is also the name of the ingredient and the dish — khar fish (কাৰ মাছ) is a whole prawn or small fish cooked in the alkaline solution with raw papaya.
Khar dish (typically raw papaya or prawn) served as the first course of a traditional Assamese meal — the alkaline note is meant to stimulate digestive enzymes and prepare the palate. Eaten with rice.
{"Banana peel ash must be made fresh: dry banana peels thoroughly, burn completely to white ash (not black charcoal), filter water through the ash three times for a concentrated lye solution","Test alkalinity: a small piece of turmeric (হালধি) in the khar water turns red if the solution is sufficiently alkaline","Add khar liquid gradually — over-alkaline food becomes unpleasantly soapy; the correct amount softens the ingredient without overwhelming the dish","Do not use metal pans for khar cooking — the strongly alkaline solution reacts with aluminium and damages iron; use clay, glass, or stainless steel"}
Commercial bottled khar (সোণ হালধি কাৰ) is available in Assamese markets as a convenience product that standardises the alkalinity — a practitioner tests even commercial khar with a turmeric strip before using. The combination of khar with mustard oil and fresh green chilli creates the basic Assamese flavour template — different from any other Indian regional cuisine. Khar cooking is considered the first course of a traditional Assamese meal (থালি, thali); a small portion of khar-cooked raw papaya or fish starts the digestive process.
{"Using incompletely burned ash — black ash from smouldering contains charcoal and impurities; the ash must be completely white for a clean lye solution","Over-using khar solution — excess alkalinity makes the dish taste soapy and inedible","Using a metal pan — reactive metals corrode in alkaline solution and can contaminate the food"}