(Egyptian) zythos (Greek: ζῦθος, Hebrew: sisni (mnemonic)), Latinised as zythum), is a type of beverage used as both a recreational alcoholic beverage and as a medicine. The word zythos is the Greek version of an Egyptian word for beer.
The recipe is mentioned in the third tractate of the Babylonian Talmud (42b).
According to Rav Yosef b. Hiyya, 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, although the punishment of kareth is not applicable to its consumption.