❄️ Cold chain

The cold chain is the unbroken cooling of a product all the way from the farm to the home fridge. For milk, that means the cooling tank on the farm, the insulated tanker of the milk lorry, the dairy's cold rooms, the refrigerated truck, the chilled display case and the fridge at home. If even one link fails to hold the temperature, the chain is said to be broken.

Milk from a healthy udder is almost sterile, and natural protective substances such as lactoferrin and lactoperoxidase hold back bacteria for another 3–4 hours after milking. FAO calls cooling to 4 °C within this time the best way to preserve quality. The Codex Alimentarius recognises only two ways of preserving raw milk: cold and the lactoperoxidase system, which at 30 °C extends its life by 7–8 hours.

In the EU, the requirements are set out in Regulation (EC) No 853/2004: straight after milking, milk is cooled to 8 °C if it is collected daily, or to 6 °C if less often; the cold chain may not be broken in transit, and milk has to reach the dairy no warmer than 10 °C. There it is quickly cooled to 6 °C if processing will not begin within 4 hours. Pasteurised milk in closed packaging keeps for 7–10 days at 5–7 °C, while for extended-shelf-life milk even brief warming above 8 °C sets off bacterial growth. As the Tetra Pak handbook puts it, the technology is only as strong as the weakest link in the chain.

Cold chain or just a fridge? A fridge or a cold room is one link, while the cold chain is the continuity of cooling across all of them, from the farm tank to your shelf. Cold is also not the same as pasteurisation: pasteurised milk in closed packaging still keeps only 7–10 days at 5–7 °C. The Codex Alimentarius recognises two ways of preserving raw milk, cold and the lactoperoxidase system, which at 30 °C extends its life by 7–8 hours. Tetra Pak puts it this way: the technology is only as strong as the weakest link.

You cannot see the chain itself, but you can see its last links. Milk and dairy products should stand in a chilled display case, not on an open shelf, and the pack should say to keep it refrigerated. Take them last at the supermarket, carry them home without delay and put them in the fridge, which should be set between 0 and 5 °C. Extended-shelf-life milk is the most sensitive to warming above 8 °C, so check that it feels cold.

In many developing countries cold is scarce: FAO notes that cooling facilities are expensive for small-scale producers there, and that milk is often carried in milk cans from simple shaded collection points. Collection and transport often account for more than 30% of processing costs, and organised producers' groups can make collection easier.