The present invention relates to methods of producing a polypeptide comprising culturing a mutant of a parent cell, wherein the mutant produces less oxaloacetate hydrolase than the parent cell, wherein the oxaloacetate hydrolase (i) has an amino acid sequence that has at least 90% identity with amino acids 1-341 of SEQ ID NO: 2: (ii) is encoded by a nucleic acid sequence having at least 90% homology with a nucleotide sequence comprising nuclotides 1157-1411, 1504-1651 and 1764-2383 of SEQ ID NO: 1: (iii) is encoded by a nucleic acid sequence which hybridizes under high stringency conditions with the nucleic acid sequence of SEQ ID NO: 1, the cDNA sequence of SEQ ID NO: 1, the complementary strand of SEQ ID NO: 1, and/or the complementary strand of the cDNA sequence of SEQ ID NO: 1: and/or (iv) a subsequence of one or both of (i) and (ii), wherein the subsequence encodes a fragment that has oxaloacetate hydrolase activity.