Laudator Temporis Acti

Dionysius of Halicarnassus, Roman Antiquities 13.11.16 (tr. Earnest Cary):

The Gauls at that time had no knowledge either of wine made from grapes or of oil such as is produced by our olive trees, but used for wine a foul-smelling liquor made from barley rotted in water, and for oil, stale lard, disgusting both in smell and taste.

οἱ δὲ Κελτοὶ οὔτε οἶνον ἀμπέλινον εἰδότες τηνικαῦτα οὔτε ἔλαιον οἷον αἱ παρ᾿ ἡμῖν ἐλαῖαι φέρουσιν, ἀλλ᾿ οἴνῳ μὲν χρώμενοι κριθῆς σαπείσης ἐν ὕδατι χυλῷ δυσώδει, ἐλαίῳ δὲ συείῳ στέατι πεπαλαιωμένῳ τήν τε ὀδμὴν καὶ τὴν γεῦσιν ἀτόπῳ...

Max Nelson, The Barbarian's Beverage: A History of Beer in Ancient Europe (London: Routledge, 2005), p. 46:

Dionysius here emphasizes his disdain for beer in one of the most virulent classical attacks on the beverage, following the notion first found in Theophrastus that beer is fundamentally rotten (presumably because of the corrupting influence of yeast, as we have seen in Chapter 3).

Diodorus Siculus 5.26.2 (tr. Earnest Cary):

Furthermore, since temperateness of climate is destroyed by the excessive cold, the land produces neither wine nor oil, and as a consequence those Gauls who are deprived of these fruits make a drink out of barley which they call zythos or beer, and they also drink the water with which they cleanse their honeycombs.

διὰ δὲ τὴν ὑπερβολὴν τοῦ ψύχους διαφθειρομένης τῆς κατὰ τὸν ἀέρα κράσεως οὔτ᾿ οἶνον οὔτ᾿ ἔλαιον φέρει· διόπερ τῶν Γαλατῶν οἱ τούτων τῶν καρπῶν στερισκόμενοι πόμα κατασκευάζουσιν ἐκ τῆς κριθῆς τὸ προσαγορευόμενον ζῦθος, καὶ τὰ κηρία πλύνοντες τῷ τούτων ἀποπλύματι χρῶνται.

Nelson, p. 51 (note omitted):

It is difficult to assess the accuracy of this statement, which is clearly again indebted to Posidonius. Diodorus seems to have misunderstood Posidonius's use of the term zūthos as a generic one for beer, taking it instead as a Gallic word for beer, which it certainly was not. There is also an ambiguity in the passage since Diodorus could be referring to one drink (a honey barley beer, made from the honeyed water remaining after honeycombs are washed) or to two drinks, namely barley beer and mead. Either interpretation is possible, especially since Posidonius speaks elsewhere of honey wheat beer, as we have seen, and since Gallic mead is known, not only from the Hochdorf grave, discussed above, but from a silver goblet (now lost) with a Gallic inscription in Greek letters which reads: 'mead of a kinsman'.