The present application discloses the identification of novel I. orientalis ADH1, ADHa, and ADHb genes, and the production and characterization of genetically modified yeast cells in which these genes were altered. Provided herein are isolated I. orientalis ADH1, ADHa, and ADHb polynucleotides and polypeptides, genetically modified yeast cells that overexpress I. orientalis ADH1 and/or contain deletions or disruptions of ADHa and/or ADHb, and methods of using culturing these modified cells to produce ethanol.