The Pasteurising Process
The Pasteurising Process
EVERYONE KNOWS THAT THE MILK YOU FIND IN THE SHOPS COMES FROM COWS. BUT HAVE YOU EVER THOUGHT ABOUT WHAT HAPPENS TO MILK FROM THE TIME IT LEAVES THE COW TO THE TIME YOU POUR IT INTO YOUR GLASS?
One place to find out is at Southview Farm. It's a small family-run dairy and milk plant in Bury, West Sussex.
Most dairies send their milk to another location to be processed. But at Southview Farm, we have been processing and bottling pasteurised milk on the farm since 2003, Raw-untreated milk has been bottled and sold form the farm since 1980.
PASTEURISATION The process of pasteurisation was invented by French chemist Louis Pasteur (1822-1895).
We process and bottle milk from our cows three days a week. On bottling days, we're able to get milk that came out of the cows that morning on the shop shelf the same morning.
The first step is to milk the cows. At Southview Farm, that's done automatically. Since 2012 two robots allow the cows to be milked whenever they want. This cutting edge technology gives the cows and staff more freedom without compromising cow welfare and milk hygiene. The cows actually visit more often, give more milk and are healthier now that they choose when to be milked. The Milking machines take the milk directly from the cows' udders to a storage tank, where it is kept at a temperature of 3 - 5C°.
All of the processing work takes place in the milk plant. That's in a separate building from where the cows are milked.
If it's time to bottle whole milk, the first thing that happens once the milk is pumped into the plant is pasteurization. In this process, milk is heated to kill bacteria and other microorganisms. It also makes milk stay fresh longer. Southview Farm uses a method called high-temperature, short-time pasteurization. That means the milk is heated to a high temperature for a just a few seconds and then cooled.
From the pasteurizing vats, milk is pumped to a homogenizer. That's a large, squat machine that blends cream particles into the rest of the milk. Normally, whole milk contains between 4 and 5 percent cream. Without homogenization, that cream would rise to the top of a container of milk because it's less dense. The homogenizer breaks down the fat molecules in the cream. It does this through a motor that drives a set of pistons that pump back and forth like the pistons in a car engine.
The pistons help pump the milk in high-pressure streams of 2,000 pounds per square inch through small tubes. This causes the larger fat molecules in the cream to break into smaller molecules. They become heavier and then are no longer able to float to the top.
If the Hughes’s aren't processing whole milk, however, they don't want that cream in the milk in the first place. To make skimmed or skim milk, they separate the cream from the milk before pasteurization using in a machine called a cream separator. Whole milk goes in, and out comes 60 percent skim milk and 40 percent cream. The separated cream is pasteurized, but not homogenized. Then it is bottled individually for sale as cream. Or it may use it to make ice cream. After the cream is removed, skim milk is processed just as whole milk is.
Milk is bottled by a machine that can be adapted to handle various sizes of containers – 2 litres, 1 litres and 500ml. Once the milk is bottled, it's stacked in crates and taken to cool storage to be delivered to local stores, restaurants, nursing homes and schools.
On bottling days, the work starts while you're still asleep in bed: One of the Hughes’s has to get up by 5 a.m. – sometimes earlier – to start processing milk! Around 7 a.m., two employees come in to help, and the three of them process milk until around 11 a.m. Then it's time pot cream or help out with the other farm chores.
We've had [older] people tell me our milk tastes like milk used to when they were growing up.