The cooling of bulk raw milk, critical in minimising contamination of milk by spoilage bacteria, pathogens and toxins, was identified as a trending non-conformance item among dairy farms during Dairysafe audits in 2018.

Additional non-conformances aligned to the milk cooling rate also identified throughout the 2018 audit program include calibration of hand-held thermometer, monitoring of milk temperature, temperature checks and refrigeration servicing.

Why is the milk cooling rate so important?

The milk cooling rate is the critical factor in controlling the risk of harmful bacteria, known as pathogens, growing. It also controls spoilage bacteria known as Pseudomonads, which are very good at spoiling protein foods by breaking down protein into shorter chain molecules and causing bitter tastes and eventually, off odours.

They get their nutrition by sending enzymes outside their body to break down the big milk proteins into bite-sized chunks that they can bring back through the cell wall and eat. These are called extracellular enzymes and they are very heat stable, so persist through dairying processes such as pasteurisation. These enzymes cause gelling of UHT milks, reduced casein yield for cheesemaking, and shorten the shelf life of pasteurised milk.

Good dairy hygiene and reducing and keeping the temperature of raw milk as low as possible on farm, during transport to processing and during storage prior to processing takes care of extracellular enzyme problems.

Active chilling on farm involves removal of heat from milk expressed from the udder at around 40°C.

How to manage the milk cooling rate within your food safety plan

Milk must be chilled to 5°C or less within 3.5 hours from the start of milking. The dairy’s food safety program identifies how milk chilling capability is checked and the frequency of checks. Records are also kept to demonstrate these requirements are in place and monitored.

The food safety program has records that show milk is maintained at 5°C or less after the primary chilling is completed. And finally, the food safety program includes how thermometers are checked for accuracy, how frequently the checks occur, and the records to demonstrate the cooling requirements have been achieved.

Food Standards Australia New Zealand (FSANZ) guidelines for raw milk collection and cooling requirements can be found here:

The Guidelines allow manufacturers to collect milk at times and temperatures other than 5°C after 3.5 hours, provided the manufacturer undertakes a risk assessment of the milk and processes it accordingly to ensure its safety.

If milk is collected above 5˚C (for example, if the tanker arrives before chilling is complete), it is the dairy manufacturer’s responsibility to ensure that temperature control procedures are validated and demonstrate equivalent control of food safety risks. Approval of the validated temperature/time parameters is required prior to milk being collected under these arrangements. Guidance on validating the time/temperature parameters can be found on the Commonwealth Department of Agriculture and Water Resources website at and also on Dairy Australia’s Manufacturing Resource Centre website at