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Āsavas and Ariṣṭas are medicinal preparations made by soaking the drugs, either in coarse powder form or in the form of decoction (Kaṣāya), in a solution of sugar or jaggery, as the case may be, for a specified period of time, during which it undergoes a process of fermentation generating alcohol, thus facilitating the extraction of the active principles contained in the drugs. The alcohol, so generated, also serves as a preservative.
Method of preparation
The required quantity of water, to which jaggery or sugar as prescribed in the formula is added, is boiled and cooled. This is poured into the fermentation pot, vessel or barrel. Fine powders of the drugs mentioned in the formula are added. The container is covered with a lid and the edges are sealed with clay-smeared cloth wound in seven consecutive layers. The rest of the process is as in the case of Ariṣṭa. If the fermentation is to be carried in an earthen vessel, it should not be new. Water should be boiled first in the vessel. Absolute cleanliness is required during the process. Each time, the inner surface of the fermentation vessel should be fumigated with Pippalī Cūrṇa and smeared with ghee before the liquids poured into it (in large scale manufacture, wooden-vats, porcelain-jars or metal vessels are used in place of earthen vessels.). 
- The filtered Āsava or Ariṣṭa should be clear without froth at the top. It should not become sour (Cukra). The preparation has the characteristics of aromatic alcoholic odour.
- Āsavas and Ariṣṭas can be kept indefinitely. They should be kept in well-stoppered bottles or jars.
- THE AYURVEDIC PHARMACOPOEIA OF INDIA, PART-II, VOLUME-II, page no 1.
- The Ayurvedic formulary of India Part-III page no 4.