Supply of high-quality dairy products is the goal of every dairy producer throughout the world. However, psychrotrophic bacteria in raw milk, generally comprising bacterial species of the genera Pseudomonas, Acinetobacter, Aeromonas, Serratia, Bacillus, Lactococcus, Microbacterium, and Staphylococcus, are of special concern to the dairy industry because they can produce heat-stable enzymes. These enzymes may withstand various heat treatments during dairy processing, causing quality defects over the product storage period. The levels and diversity of psychrotrophic bacteria in raw milk are tightly linked to natural habitats, milking practices, and hygiene practices of farms in different countries. Most psychrotrophic bacteria can form biofilms on various milk storage and processing equipment, which serve as persistent sources of microbial contamination due to their biotransfer potential. A comprehensive review of the diversity of psychrotrophic bacteria in raw milk, the spoilage potential of these bacteria, the specific technological problems caused by biofilms and heat-resistant enzymes, and potential strategies for controlling dairy spoilage starting at the farm level is needed for improving our understanding of these spoilage bacteria.