⚙️ Bulk milk cooler

A bulk milk cooler is a large stainless steel tank. On the farm, milk is cooled in it and stored until the milk tanker arrives. The tank has double walls with polyurethane foam insulation between them. Inside, a stirrer runs: it keeps the temperature even throughout and stops the cream from rising.

Milk comes out of the udder warm, at about 37 °C. It has to be cooled to +4 °C as fast as possible, usually within 2–3 hours after milking. The Tetra Pak handbook advises doing it within 2 hours at most. A plate pre-cooler is often fitted before the tank: the milk first gives off heat to cold water and is then cooled the rest of the way in the tank. This saves electricity and keeps the quality better.

Tanks range from 150 litres on a small farm to 10,000 litres and more. The size is worked out from the number of milkings: a “two-milking” tank receives half its volume at a time, a “four-milking” one a quarter. Milk is stored at 3–4 °C. The tanker collects it once a day or every other day. After each emptying, the tank is washed, often automatically.