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Posca was a popular drink in ancient Rome and Greece, made by mixing sour wine or vinegar with water and flavouring herbs. It originated in Greece as a medicinal mixture but became an everyday drink for the Roman army and the lower classes from around the 2nd century BC, continuing to be used throughout Roman history and into the Byzantine period. It was not usually drunk by the upper classes and was associated with the peasants. It was made by reusing wine spoiled by faulty storage and had important dietary advantages. As well as being a source of liquid, it provided calories and was an antiscorbutic, helping to prevent scurvy by providing vitamin C. Its acidity killed harmful bacteria and the flavouring helped to overcome the bad taste of local water supplies.
Posca was increasingly heavily used by the Roman army during the Republican period when it became a standard beverage for soldiers. The drinking of quality wine was considered a sign of indiscipline, to the point that some generals banned imported vintage wine altogether. Appian records both posca and wine as being among the provisions of the army of Lucullus in his Spanish campaign of 153 BC. It had evidently become part of the customary rations by the 1st century AD; the Christian Gospels describe Roman soldiers offering Jesus sour wine on a sponge  during the Crucifixion. The Historia Augusta records that by Hadrian's time sour wine was a standard part of the normal "camp fare" (cibus castrensis). A decree of 360 AD instructed the lower ranks of the army to drink posca and wine on alternate days.
Although it was primarily associated with soldiers and the lower classes, some higher-ranked Romans also drank posca to express solidarity with their troops. According to Plutarch, Cato the Elder was particularly noted for liking posca. Girolamo Cardano, in his Encomium Neronis, Basel (1562), attributed the superiority of the Roman armies to only three factors: the great quantities of levies, their sturdiness and ability to carry heavy weights due to training, and good foods such as salted pork, cheese and the use of posca as a drink.
The word posca is derived from either the Latin potor (to drink) or from the Greek epoxos (very sharp). It was an unfamiliar beverage in the largely Greek-speaking eastern Mediterranean region, where sweet wines were preferred. As the Greeks lacked a word for posca, sources written in Greek, such as Plutarch and the Gospels, use the word οξος (oxos, vinegar) in its place (translated as acetum in the Vulgate Bible). The word eventually migrated into Greek from about the 6th century AD onwards as the Byzantine army continued the Roman tradition of drinking what they termed phouska.
No recipes for posca are known to have survived. An approximate recreation of the beverage can be made by combining 1½ cups of vinegar with ½ cup of honey, 1 tablespoon of crushed coriander seed and 4 cups of water. The mixture should be boiled in a saucepan to dissolve the honey before being allowed to cool to room temperature. After straining out the coriander seeds, it can be served.
- Showalter, Dennis E. Soldiers' Lives Through History, pp. 36-37. Greenwood Publishing Group, 2007. ISBN 0-313-33348-3
- Luke 23:36
- Cardano, Girolamo. Nero, An Exemplary Life (translated by Angelo Paratico) pp.185-6, Inkstone Books, Hong Kong, 2012. ISBN 978-988-99939-6-2
- Kaufman, Cathy K. Cooking in Ancient Civilizations, p. 182. Greenwood Publishing Group, 2006. ISBN 0-313-33204-5