From Halopedia, the Halo wiki
Kasna was a rare alcoholic beverage produced by the San'Shyuum during the reign of the Forerunners. It was described as a greenish liquid with a pungent, sweet and sour odor. It is also noted for leaving green stains on whatever is used to serve it. It was described by Forerunners that imbibed it as burning the belly and softening the edges. The Confirmer was gifted several bottles of kasna from the San'Shyuum quarantined on their homeworld, Janjur Qom, from their finest reserves. Splendid-Dust-of-Ancient-Suns also drank it while on Installation 00 during the reintroduction in order to bring himself to speak to the other Forerunners present about secret knowledge he held.
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