Have you ever wondered how milk is processed before it makes its way into shops?
After the milking process on a dairy farm, milk is transported to processing plants where it goes through several processes before it finally makes its way to shops.
I will go through these steps and explain how each one works.
In this article I will discuss:
What is dairy milk and where does it come from?
Dairy milk comes from cows on dairy farms where cows are milked daily, sometimes up to 3 times a day. Each cow, depending on the breed, can give anywhere between 3 and 30 liters in a day.
Dairy cows are mammals and produce milk in their udders by the mammary glands. The main function is to feed their young.
Young cattle, called calves, drink milk until they are weaned when they are old enough to start grazing grass and pastures.
The weaning age of calves is around 12 weeks and they should weigh at least around 100 kg (220 lbs).
Milk collection from the farm
After milking, the milk is stored in cooled tanks on the farm until the dairy tankers collect it. This will usually be every 24 to 48 hours.
These tankers have special insulated stainless-steel tanks that keep the milk cold during transport to dairy processing facilities.
These tanker drivers are usually accredited milk graders and they accept milk depending on sight, smell and temperature.
Milk samples are also taken from the farm storage tanks that are tested for things like milk fat content, protein content and bacterial levels.
Farmers are paid for their milk according to the grade and quality of the milk and all of these factors are taken into account.
All throughout the milk processing process the milk is kept cold to prevent bacteria from growing and spoiling the milk.
How is milk processed?
Once the tankers arrive at the milk processing facility, samples are taken again. This time the samples are tested for temperature and the presence of antibiotics.
Thereafter the milk is pumped from the tanker through cooling tubes into big stainless steel storage tanks.
These tubes cool the milk down to around 4°C (39.2°F) so it’s already cold when it enters the storage tanks.
From here there are several processes that milk goes through to end up in the final product you see on the supermarket shelves.
Milk clarification
Milk clarification is the initial process where solid particles like dirt, precipitated milk proteins and bacteria, are separated from the milk.
This is done by a machine called a clarifier. It separates all these particles from the milk through a process called centrifugation.
I talk a bit more about milk centrifugation in my article about how skimmed milk is made.
Pasteurization
Pasteurization is the process where milk is heated to 72°C (161.6°F) for at least 15 seconds, after which it is cooled down immediately. This kills any microorganism, including harmful bacteria as well as bacteria that spoils the milk.
In this way the milk has an extended shelf life and is safe to consume.
This process was originally introduced to control the bacteria in milk that causes tuberculosis.
This in no longer the main reason since stricter management controls and testing virtually eliminates these tuberculosis bacteria from the dairy supply chain.
There are other bacteria present in some milk, like Coxiella burnetiid, that causes Q fever in humans.
These bacteria are killed at 71.7°C (161.06°F) for 15 seconds or more.
A PasLite test is a test run after pasteurization to test if the process was effective.
UHT (Ultra High Temperature) is like pasteurization, but just at a much higher temperature of 135°C (275°F), after which the milk is cooled down rapidly again.
This high temperature ensures that all microorganisms and spores are eliminated for ultra-long shelf life.
Homogenization
Homogenization is the process where milk is pumped through fine nozzles under very high pressure (10 – 25 MPa /100 – 250 bar) that breaks up the milk fat globules and distributes them more evenly throughout the milk.
This prevents the milk and cream (that contains the milk fats) to separate over time, giving the milk a more uniform consistency.
Centrifugal separation
The cream (which contains most of the milk fat) and milk is separated by centrifugation.
Afterwards, these two parts are mixed back together again in certain ratios to give you the different milk types according to their fat content (full fat, reduced fat, low fat and skim milk).
You can read all about centrifugal separation in my article about skim milk.
Vitamin fortification
Some countries, like the US, have laws that require vitamins to be added to milk to increase its nutritious value. Vitamins that are mainly added are Vit A and Vit D.
Final thoughts
These are the main processes involved in getting milk from the farm to the shelf.
There are more processes, but they have more to do in the production of powdered milk, lactose-free milk, cheese, yogurt etc.
So next time you have a look at the white stuff in the supermarket, you will know all the processes and people involved in getting it there in the first place.
Happy cooking!