🔄 Filling

Filling is the packing of finished milk into cartons, bottles, jars and cups at a dairy plant. After pasteurisation at 72–75 °C for 15–20 seconds, the milk is cooled and fed through buffer tanks to the filling machines. Under EU rules, packages are sealed immediately after filling, at the same establishment where the last heat treatment took place, and in a way that makes any opening visible.

Ultra-pasteurised (UHT) milk, heated to 135–150 °C for a few seconds, is cooled to about 20 °C and filled aseptically — into pre-sterilised packaging under sterile conditions. It is then commercially sterile and keeps without a fridge. Sterilised milk in bottles is heated above 135 °C, cooled to 30–70 °C (lower for plastic), filled into clean bottles and sterilised again once sealed. Modern aseptic machines fill up to 40,000 cartons an hour.

Milk cartons came from Sweden: Tetra Pak, founded in 1951 in Lund, delivered its first machine for tetrahedral cartons in 1952, demonstrated aseptic filling of milk in 1961 and in 1969 presented the rectangular aseptic brick-shaped carton.

Pasteurised or UHT? The difference lies in heat and filling. Pasteurised milk is heated to 72–75 °C for 15–20 seconds, packed under clean conditions and kept cold, so it lasts 7–10 days. UHT milk is heated to 135–150 °C for a few seconds and filled aseptically into pre-sterilised packaging, so it is commercially sterile and keeps without a fridge. Sterilised milk in bottles is a third route: it is heated above 135 °C, filled, and sterilised again once sealed.

Read the heat-treatment line on the pack: «pasteurised» milk sits in the chilled cabinet and carries a short date, while «UHT» or long-life milk stands on an ordinary shelf and needs the fridge only after opening. The seal must show if it was opened, and a carton with a foil layer keeps out light. Supermarkets, dairy shops and petrol-station shops sell both kinds.

Why it matters to you. Packaging needs to protect milk from light, which destroys vitamin B2 and causes a “cardboard” off-flavour. Under lighting of 1,500 lx, milk in a clear glass bottle loses about 10% of its vitamins B2 and C in 2 hours, while milk in a carton loses almost nothing. A carton with a foil layer protects almost completely against light and oxygen. Unopened pasteurised milk keeps for 7–10 days at 5–7 °C, and aseptically packed milk keeps without refrigeration as long as the package is intact.