Bacteria from milk tankers can form multispecies biofilms and produce heat-stable enzymes. In this study, milk was exposed to multispecies biofilms in stainless steel vessels and was then used to produce ultra-heat-treated (UHT) milk, which was stored for 5 months. The UHT milks were assessed for microbial counts, free peptide concentration and pH. The free peptide concentration, which indicated proteolysis, was higher in UHT milk that had been exposed to multispecies biofilms than in untreated UHT milk. Biofilm formation may be promoted in milk tankers that are not properly cleaned, which may compromise the quality of the final dairy product.