Bitter peptides are the bitter-tasting peptides formed during enzymic protein hydrolysis that can impair sensory quality. Casein-derived bitter peptides are a particular problem in cheesemaking, where excessive proteolysis produces harsh notes, and they can also trouble soy products and the protein hydrolysates used in sports nutrition and clinical feeds. Treatment with peptidases, especially aminopeptidases that trim hydrophobic terminal amino acids, may eliminate quality problems attributable to bitter peptides. Their management is a core skill in dairy and protein-ingredient manufacture, balancing the desired protein breakdown against the sensory penalty of going too far.