Origins of the Phrase

In vino veritas:“in wine [there is the] truth".

It is also known as a Greek phrase “Ἐν οἴνῳ ἀλήθεια” En oino álétheia, which has the same meaning. The author of the Latin phrase is Pliny the Elder; the Greek phrase is attributed to the Greek poet Alcaeus. The Greek poet Alcaeus is the oldest known source for the phrase. The Roman historian Tacitus described how the Germanic peoples always drank wine while holding councils, as they believed nobody could lie effectively when drunk.

The phrase is often continued as, "In vino veritas, in aqua sanitas", i.e., "In wine there is truth, in water there is health."

Similar phrases exist across cultures and languages. In Chinese, there is the saying, "酒後吐真言" ("After wine blurts truthful speech"). The Babylonian Talmud (תלמוד בבלי) contains the passage: "נכנס יין יצא סוד", i.e., "In came wine, out went a secret".

It continues, "בשלשה דברים אדם ניכר בכוסו ובכיסו ובכעסו", i.e., "In three things is a man revealed: in his wine goblet, in his purse, and in his wrath."

(Information taken from Wikipedia)