How is milk made? It may be more complicated than you think

When you hear the question “how is milk made?” you might be tempted to answer: “By cows”.

But there are a lot of processes that happen with milk between the time a cow is milked and the time you take a bottle out of the fridge for your breakfast cereal.

So whether you buy whole, cut, or standard milk, how does the manufacturer arrive at the end result, does the nutritional value differ, and what is milk really?

All the milk you buy from stores is separated, standardized, pasteurized and homogenized. It is then formulated to make milk with different fat or cream content.


According to Anchor, once the milk arrives from a farm in a tank truck, it is first separated into cream and skim milk.

The milk is either separated by letting gravity do its job and letting the cream rise to the top, or by centrifugal separation, which involves spinning the milk very quickly to separate it.

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Some of the skimmed milk is filtered after this process to further separate it.

One of these separated parts is called permeate, which is mainly made up of water, lactose, vitamins and minerals.

The permeate is reused later in the milk making process.

A Fonterra spokesperson said separation was considered a standard step in milk processing. The milk was then standardized with added cream to produce the desired fat to protein ratio.


Milk in New Zealand is pasteurized.

Anchor said pasteurization at its plant involves heating milk to 72°C to 75°C for 12 to 15 seconds.

Milk retains its nutritional value during processing, except for some loss of B vitamins during pasteurization.


Milk retains its nutritional value during processing, except for some loss of B vitamins during pasteurization.

Dairy scientist Dr Siqi Li said that like raw meat and eggs, milk contains bacteria that can cause illness. These bacteria were much more prevalent over 100 years ago when milk pasteurization was not common.

Li said studies showed that in the early 1900s in the United States, more than 65,000 people died of tuberculosis from milk. Pasteurization solved this problem.

The nutritional content of the milk was not changed by the processes the milk went through except under heat, Li said.

Anchor said that during pasteurization, some B vitamins were reduced by 5-10%.


Farmer Logan Johnson of Farm Fresh South in Southland, which sells raw milk, doesn’t think most consumers know what milk goes through before it appears on store shelves.

Straight-bottled milk will naturally separate, Johnson says. To maintain the same taste and texture of the milk in each bottle and to avoid separation, the milk is homogenized.

Anchor says it involves squeezing the milk through a narrow space at high pressure. This process breaks down the milk fat droplets into smaller droplets. This keeps the fat evenly distributed throughout the milk.

No standardized, homogenized or pasteurized milk for this calf, but milk purchased from retail stores has all gone through several processes.

Joseph Johnson / Stuff

No standardized, homogenized or pasteurized milk for this calf, but milk purchased from retail stores has all gone through several processes.

Johnson said milk straight from a cow has seasonal variations in taste, due to changes in grazing, length of lactation and weather conditions.

Some people who buy raw milk have these differences, Johnson says.


Standardizing milk means controlling one part, such as fat or cream content, while modifying the rest so that it can be sold, for example, as full cream or filling.

This normally involved reducing the fat content by adding skimmed milk or removing the cream itself.

Anchor says it mixes cream, skim milk, retentate and permeate to make a range of different milks.

More cream is used to produce creamier types of milk, with less cream for light or low fat milk – and none for skimmed milk.

By controlling the exact fat content, or adding or reducing permeate or skimmed milk, the texture and nutritional level of the milk is kept constant.

At this point, the permeate can be added back to the skimmed milk to ensure the protein level and taste are consistent.

All milk has a price.

There are various reasons for the price differences. The raw materials played a big role, or for example, fortification and addition of calcium or additional processing to remove lactose from the milk as well as other factors regarding processing times, set-up times, cleaning, processing efficiency, storage, sell rate and more,” the Fonterra spokesperson said.

Retailers set prices at their own discretion.

Dairy standards

New Zealand’s deputy director general for food safety, Vincent Arbuckle, said the Australian and New Zealand Food Standards Code set out the regulatory requirements for milk.

“Milk” specifically meant animal milk, which was to be used for drinking or for processing.

Skim milk is specifically regulated, but there are no definitions for full cream, filling, or other terms often used on milk bottles.

Skimmed milk must not contain more than a specified amount of milk fat and not less than a specified amount of protein.

On all milk, any nutrition claims must meet the food standards code, he said.

The law also specified which vitamins or minerals could be added to milk to fortify it. Vitamin A, D, calcium and riboflavin fell within those specifications, Arbuckle said.

Arbuckle said the Department of Health has defined milk to some extent. It was considered a food that had undergone some processing, but had retained most of its physical, chemical, sensory and nutritional properties.

These foods were usually processed to make the foods safer or healthier, he said.

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