Lewis & Short

cŏ-ăcesco, ăcŭi, 3, v. inch. n., to become acid or sour (rare but in good prose).

  1. I. Prop.: genus uvae, Varr. R. R. 1, 65, 2; cf.: ut non omne vinum, sic non omnis aetas vetustate coacescit, Cic. Sen. 18, 65; Dig. 33, 6, 9 pr.: secunda mensa in imbecillo stomacho coacescit, Cels. 1, 2: si coacuit intus cibus aut computruit, id. 4, 5 fin.
  2. II. Trop (the fig. drawn from wine): quare cum integri nihil fuerit in hac gente plenā, quam valde eam putamus tot transfusionibus coacuisse? to deteriorate or become corrupt, Cic. Scaur. 22, 43 B. and K.; cf. id. Sen. 18, 65 supra.