Interactive lesson

Milk without disease, step by step

Interactive lesson: from udder to pan — clean milking, straining, chilling to 4–6 °C, pasteurising at 63 °C, washing up and signs of spoilage.

Free sample Chapters 1 and 2 (8 steps) are free. The full lesson comes with the Milk: hygiene, straining, pasteurising module. Already bought? Unlock

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The whole lesson as text

1. Why milk is so delicate

Milk is the perfect food, for people and for bacteria.

Clean from the udder — Milk from a healthy udder is almost free of bacteria. Everything else gets in on the way: from the skin of the udder, from hair and dust, from hands, from the bucket and the pans.
You can't see it — You can't see, smell or taste bacteria in milk. Milk that looks perfect can carry Brucella or listeria.
Cold, and fast — Chill milk to 4–6 °C (39–43 °F) as soon as you can, within 2 hours of milking at the latest.
Heat with a thermometer — Pasteurising: 63 °C (145 °F) for 30 minutes or 72 °C (162 °F) for 15 seconds, then chill fast. A thermometer is not optional.

Why: Milk holds sugar, fat, protein and water, at body temperature. A litre of fresh milk left a few hours somewhere warm becomes a litre in which bacteria are counted in millions. Some only sour the milk; others cause listeriosis, brucellosis, tuberculosis and severe poisoning.

Between 10 °C and 40 °C (50–104 °F) bacteria multiply fastest; some double in 20–30 minutes.
The UK, Ireland, the US and Canada are free of brucellosis in cattle, but bovine TB is common in parts of England, Wales and Ireland. Always pasteurise milk from a herd you don't know.

2. Raw milk: the decision

The risk of raw milk isn't there every day, but it is real and it isn't the same for everyone.

Pregnant women — Listeria crosses the placenta. No soft raw-milk cheese, and no cream or kajmak from unheated milk.
Young children — In children, especially under 5, E. coli is more likely to cause kidney failure. A small number of bacteria is enough.
The elderly and the sick — People over 65 and everyone with a weakened immune system: diabetes, cancer, transplants, steroids, liver and kidney disease.
The house rule — All milk for drinking, yoghurt and soft cheese is pasteurised. Nobody drinks raw milk from a herd that hasn't been tested for brucellosis and TB.

Why: A healthy adult drinking milk from a known, tested herd has a small risk. A pregnant woman, a two-year-old or a grandfather on medication has a much larger one, and the consequences can be permanent. Decide once, for the whole family, and write the rule down.

Sixty days of ripening is not a guarantee: listeria and E. coli can survive longer, especially in cheese that isn't very acidic or very salty.
When you buy from a neighbour, ask: has the herd been tested, has any animal been treated, is there any mastitis and was the milk chilled?