Visual changes and bitterness were observed at apparent peptidase activities ≥ 0.05 pkat mL−1 in UHT milk. In UHT milk containing 0.03 pkat mL−1, bitterness was occasionally described after 4 months of storage. We assume that, during longer storage, these UHT milk samples would also have been classified as bitter. In previous studies, higher peptidase activities were often employed when examining the effect of enzymes added to UHT milk on the storage stability, or otherwise the peptidase activity produced during growth of Pseudomonas spp. in raw milk was not determined. In other studies, peptidase activities similar to those used in this study were added to UHT milk, and the milk was observed for signs of visual deterioration, but not for bitterness