(Egyptian) zythos (Greek: ζῦθος, Hebrew: sisni (mnemonic)), or zythum (Latinized form), is a type of beverage, used as both a recreational alcoholic beverage and as a medicine. The word zythos is a Greek version of an Egyptian word for beer[1].
The recipe is mentioned in the Third Tractate (Pesahim) of the Babylonian Talmud.[2]
According to Rav Yosef, it contains 1/3 barley, 1/3 safflower seed and 1/3 salt. Rav Papa substituted wheat for barley. The ingredients are steeped, roasted and ground before drinking.
Drinking zythos is dangerous for sick people and for pregnant women. It works as both a laxative and an antidiarrhoeal.
It is forbidden during Passover, because it contains barley, thus making it chametz. Karet is not applicable to its consumption.