Steve Lehman, MMPA Raw Milk Compliance Manager
Milk cooling, along with sanitary milking procedures and clean equipment are the three keys to producing top quality milk. Providing top-quality milk and milk products to our customers has enabled MMPA to become a preferred supplier of raw milk and milk products across
the country. Milking procedures and equipment provide the “seed” for bacterial growth; compromised cooling magnifies the growth of bacteria that is present.
The Pasteurized Milk Ordinance (PMO) requires that milk be cooled to 50° F within 4 hours of the start of milking, and allows for an additional two hours to bring the milk to 45° F. The blend temperature must not exceed 50° F after the first milking. Keeping your mechanical cooling systems (compressors, chillers, and bulk tank interval timers) operating properly, along with maximizing well water pre-cooling enables these temperatures to be met while obtaining the maximum efficiency of energy used.
Cooling milk quickly to 36-38° F or less enables milk to be sent to high value and long-distance markets. While milk tankers are well insulated and cooling rinses are employed when practical, the milk still needs to absorb any heat remaining from tanker cleaning and storage in the summer sun.
Marc Roberts, Roberts Dairy Service Owner
Maintaining your milk cooling system’s efficiency is critical, especially when summer heat adds extra strain. Pre-cooling with well water can
significantly reduce the cooling load, removing up to 2/3 of the heat. To optimize this, flush the well water side of your pre-cooler to eliminate rust and mineral buildup that hinders heat transfer. Ensure all water lines to and from the unit are clear of obstructions caused by mineral deposits. Also, consider if your current milk flow rate exceeds your system’s capacity.
Regularly check refrigerant pressures and levels in your compressors. For water-cooled units, verify adequate water flow and a clean heat exchanger. Air-cooled compressors require clean condensers with straightened fins and unobstructed airflow. Ensure condenser fans and their controls are clean and functioning correctly. Many power providers offer rebates for cooling system tune-ups, so contact your local dairy equipment dealer for this service. Proactive maintenance ensures efficient cooling and protects milk quality during hot months.
Sudeep Jain, MMPA Director of Quality
Bacterial growth in milk depends on six factors: food, acidity, time, temperature, oxygen and moisture (FAT TOM). Milk drawn from the udder is around 101–102°F— which is also the optimum growth temperature for a variety of bacteria. Milk’s unique nutrient-rich composition (food and moisture), nearneutral pH (acidity) and dissolved oxygen make it a perfect environment for bacteria to multiply, potentially doubling every 20 minutes. To preserve the quality of milk, milk producers and processors must control the temperature by cooling the milk rapidly (time).
To maintain milk quality, rapid cooling to 36–38°F is essential. If not cooled quickly, harmful bacteria like Staphylococcus aureus can grow and produce toxins that survive pasteurization and cause illness. Spoilage causing bacteria may also grow,
creating off-flavors, lactic acid and a sour taste. Additionally, heat-stable enzymes like lipases and proteases can degrade fat and protein, reducing shelf life and affecting taste and quality.
Modern dairy processing emphasizes rapid cooling to prevent these issues, ensuring better flavor, functionality and shelf life. By controlling temperature and bacterial growth, milk producers and processors can maintain high-quality milk and dairy products.
This article was originally published in the May/June 2025 issue of the Milk Messenger. Subscribe »