As the weather heats up, keeping milk cool becomes critical. Food safety, product flavor and shelf life - and, ultimately, consumer satisfaction - depend upon quickly cooling milk and holding it at the proper temperature. The FDA's Pasteurized Milk Ordinance (PMO) states that milk must be cooled to 45 degrees or less and maintained at that level; check with your milk marketer, though, as many require lower temperatures. Distance to market, product manufactured and customer specifications all factor into desired milk temperatures.
We've outlined a milk cooling system checklist and shared top tips to help you avoid cooling issues and keep milk at peak quality:
1. Clean compressor radiators. Over time, the radiators become dusty and should be blown out with compressed air. To remove stubborn buildup, some service people use a special spray foam cleaner and water. Be careful to keep all electrical connections and fan motors dry. Check radiator fins to make sure they have not been bent by a loose fan blade or other mishap. They can be straightened with a tool specialized for this purpose.
2. Are the compressor's cooling fans operating correctly? Check that airflow around the compressors is adequate. If the area around the compressors has been closed for winter, make sure that it is opened to enable good airflow.
3. Ensure that Freon levels are adequate for the cooling system. Some systems have sight glasses to indicate low levels, but others do not. If cooling is taking longer than usual and airflow is not an issue, call a service technician to check Freon levels. Fix any Freon leaks detected during servicing. Putting off the repair only delays the inevitable and risks a cooling system failure.
4. Monitor milk temperatures closely. We recommend that the bulk tank shuts off at a maximum of 38 degrees. The bulk tank thermometer should be checked for accuracy and adjusted or, at the very least, note the deviation from the accurate thermometer.
5. Turn on the bulk tank following the manufacturer's recommendations. Typically, if the bulk tank is empty, start the tank after milk from a few cows has gone into it. If there is milk in the tank, and depending on the agitator control, you may need to manually start the agitator to blend the warm milk with the cold milk as you start milking.
6. Use a temperature recording device. The PMO requires any bulk tank manufactured after January 1, 2000, to have a chart or temperature recorder. Many bulk tanks manufactured prior to this date still are in use and can be retrofitted with temperature recorders.
The main benefit of a temperature recorder is that it provides documentation of temperatures. Both cooling and wash temperatures are recorded on a time scale. Events that can be observed are: when the bulk tank was turned on, how long the milk took to cool, when the milk was picked up, when the wash cycle started and its temperatures.
7. Communicate to employees and family members the importance of milk cooling. Explain the need to contact management, the milk purchaser and service technicians if something goes wrong. In the event of a milk cooling problem, notify your milk buyer as soon as possible so that they can test milk quality. In many areas, if a producer's milk damages any other milk on the truck or in the plant, the producer may be liable for the costs of any damaged milk.
Data triggers awareness
A Minnesota producer installed a temperature recorder in an older bulk tank about two years ago. He says it is the first thing he looks at when entering the milk house to monitor the cooling and wash cycles. Any changes in the wash temperatures lead him to check the hot water supply. If temperatures during cooling are higher than usual, or it is taking longer to cool than normal, the cooling system is checked.
Temperature recorders are installed with one of two chart options: two-day or seven-day charts. These charts need to be changed at either the two- or seven- day interval. The charts need to be signed by the person changing it, and it must identify the producer. They also need to indicate the date they were installed and which tank the chart is for, if there is more than one tank. The PMO requires that the old charts be filed for six months for possible inspection.
Temperature data loggers (such as the HOBO brand) can assist in troubleshooting cooling and cleaning challenges. The data loggers can be deployed in a bulk tank and set to record at varying intervals, then downloaded to a laptop to graph the temperature events.
When troubleshooting bacteria, we typically set the data logger to take a reading every 60 seconds. This provides tremendous data, down to even how the cooling system performs with different groups of cows, and the loading rate of milk.
Another nice feature of using a data logger is that, after downloading data and graphing the events, we print a copy for the dairy producer and save the information for future comparison. We also email a copy to the service company involved so that they can see exactly where the cooling system deficiencies are.
We recently used a data logger on a Pennsylvania farm to determine whether high bacteria counts were caused by milk cooling issues. After reading the device on the farm, the producer could visually see the problems. His milk was taking too long to cool, and his blend temperatures exceeded 45 degrees. He called his service company for a complete evaluation of the cooling system. After the repairs, we again used the data logger to confirm the cooling issue was resolved.
There are a number of other technologies available to cool milk. Plate coolers use well water in a single- or dual-pass process to remove heat from the milk before it enters the tank, allowing the tank to cool more efficiently. Chillers use food-grade glycol and water in a dual-pass system to rapidly cool milk. They are more common on large dairies, which directly pipe milk into tankers or into on-farm storage silos. When plate coolers or chillers fail, a refrigeration specialist is usually required.
Additionally, there are a number of alarm systems that can be installed on the farm to let the producer know when milk is not being cooled properly. Alarms can be as basic as a colored lightbulb indicating that the bulk tank is on or off, to computerized systems that can notify the producer via text messages that the milk is not cold.
Once a cooling issue occurs, the results likely are irreversible, and milk quality is degraded. As a guideline, if cooling problems occur on the first milking, cooling it down and adding additional milkings will not help the situation. This checklist is a great place to start to prevent summertime cooling issues.