During ripening of cheese, many biochemical processes take place, which are essential for favour development. The breakdown of caseins is a prerequisite for favour development. A good balance between proteolysis and peptidolysis prevents the formation of bitterness in the cheese. For this reason, it is necessary to focus on starter cultures with highly active peptidases, which should be active in the cheese matrix. Amino acid converting enzymes (AACEs) are involved in the degradation of amino acids, which are liberated during proteolysis. Their activity results in various volatile (favour) components; most notably the degradation of methionine results in favour active sulphur compounds. AACEs involved in degradation of methionine and other amino acids were identied and their role in (cheese) favour formation is described. At least two pathways leading to the formation of sulphur compounds were identied. Overproduction of one of the enzymes involved, results specically in a higher formation of sulphur compounds. This result, together with the observation that favour production is highly strain specic amongst various lactococcal bacteria, oers a new potential for industrial applications.