Psychrotropic bacteria can produce extracellular, heat-resistance enzymes that remain active during the thermal processing of milk. Psychrotropic populations at densities of 10⁶–10⁷ colony-forming units (cfu) per milliliter synthesize these enzymes at concentrations high enough to cause alterations in milk stability and in dairy products. These enzymes may also cause sensory defects and technological problems, such as loss of cheese texture and gelation of ultra-high-temperature (UHT) milk.