Bitterness, a common flavor defect in Cheddar and Gouda cheese, results from the accumulation of hydrophobic bitter peptides to concentrations higher than their taste thresholds. Formation of these peptides is directly related to the activity and specificity of the lactococcal cell envelope protease (lactocepin) and the coagulant, chymosin. Degradation of these peptides is related to the activity and specificity of peptidases derived from the starter and non-starter bacteria present in the ripening cheese. Therefore, by controlling the activity and specificity of the proteolytic enzymes of lactic acid bacteria it should be possible to control bitterness. This paper will focus on the contribution of lactocepin to the formation of bitter peptides and a method for altering lactocepin specifically. Additionally, efforts to characterize the proteolytic enzyme system of an adjunct culture known to reduce bitterness,Lactobacillus helveticus CNRZ32, will be discussed.