A new study posits that climate change occurring in Europe could impact the microbiological quality of raw milk. 

The study used a probabilistic model to quantify the concentration of Escherichia coli in raw milk and used that data to predict what might happen to raw milk supplies in France under climate change conditions. It included four modules: initial contamination, packaging, retailing, and consumer refrigeration.

"Overall, the model and its outputs provide an insight on the possible microbial raw milk quality in the future in France due to higher temperature conditions driven by climate change," says the study.

Although some organisms do not survive in the increased temperatures projected to occur with climate change, some E. coli strains are thriving. The worry is that these organisms will adapt and be able to withstand the pasteurization process. Many European consumers drink unpasteurized, raw milk, including French citizens. 

Initial microbial counts in the study were taken from 2019, from a dairy in Saudi Arabia, to reflect the impact of the temperature and climate differences and predict the changes that might occur in Europe because of climate change. The temperature of the milk cooling tank on the farm was assumed to comply with French legislation of below 4 °C. E. coli counts from bulk milk tanks were collected and analyzed as part of routine monitoring and then used to assess contamination after the milking step. 

According to the study, microbial growth was determined through different scenarios of time and temperate storage, reflecting the raw milk supply chain in France. The country has a 2 log colony forming units/ml (CFU/ml) limit for E. coli; some of the average initial concentrations of E. coli in raw milk were estimated at 1.31 log CFU/ml. These concentrations were shown to increase at the end of the supply chain depending on temperatures and public storage times. At retail, predicted E. coli concentration was 1.53 CFU log/ml after 12 hours at 8 °C (46.4 °F).

In France, dairy milk farming is a mix of small-, medium-, and large-scale operations, with small being the most prevalent. Raw milk can be sold at local markets within only 12 hours after milking, provided that the storage temperature is lower than 8 °C (46.4 °F) and is consumed within 72 hours. The French standard mandates that temperatures must be maintained at 2 °C–4 °C (35.6 °F–39.2 °F) during raw milk packing.

“The current practice of drinking raw milk in France might need to be revisited since the current hygiene criteria for packaged raw milk might be difficult to meet in the future if hotter conditions become the standard,” the study concluded.