Here’s How Milk Gets From the Cow to Your Supermarket

It’s easy to grab a jug of milk from your local grocery store without thinking about how it got there. But recent news about the U.S. Department of Agriculture testing the national milk supply for bird flu has raised plenty of questions about how milk is extracted, processed, and handled before getting to consumers.  

Dairy industry experts stress that this is a tightly regulated process. “Milk is probably the most tested product on the market — it is extremely safe,” says Jeff Semler, principal agent with University of Maryland Extension. Martin Wiedmann, DVM, PhD, veterinarian, food scientist, and professor at Cornell University College of Agriculture and Life Sciences, agrees. “It’s one of the most highly regulated foods in the U.S.,” he says.

With that in mind, Food & Wine tapped six dairy experts, along with an infectious disease physician, to break down exactly how milk gets from the cow to store shelves. 

Milk is first collected from cows using a vacuum system

While the process of milking cows used to be done by hand, modern dairy farms will typically use milking machines. “The whole process is done in the milking parlor, where milking operators follow proper milking procedures to ensure harvesting milk of high quality,” says Izabella Maria Michelon Toledo, PhD, extension assistant scientist at University of Florida Institute of Food and Agricultural Sciences. 

The exact procedures vary slightly by dairy farm, says Kelly Nichols, PhD, assistant professor at the University of California Davis Department of Animal Science. In some farms, a farm worker will clean the cows’ udders before attaching a milking machine. “Alternatively, some dairy farms use automated milking systems which employ robotic arms and sensors to clean the udder and place the milking machine,” Nichols says. “In these systems, cows can visit the milking system on their own schedule.”

The milking machine is designed to be comfortable for the cow, Nichols says. “It uses a sequence of suction and pulsations to stimulate let-down of milk from the udder,” she says. 

Cows are usually milked two to three times a day and, once they’re in the milk parlor, the collection process takes about 10 minutes, Toledo says. 

“The milk flows directly from the cows to a refrigerated holding tank to maintain freshness and quality,” says Efrain Valenzuela, dairy agricultural literacy director from Dairy Council of California.

Milk briefly sits in a holding tank before it’s collected

Most farmers sell their milk to a processor, says Steven Beckman, MS, manager of the Davis Dairy Plant at South Dakota State University. “For those farms, cooled milk in the bulk holding tank at the farm is transferred to a milk truck by a licensed and inspected milk hauler, typically within 24 hours of milk collection,” he says. Depending on how busy a dairy farm is, the milk collection truck may visit once or several times a day. 

A sample of milk is taken to be tested for bacteria, antibiotics, and other substances that are not allowed in the human food supply, Wiedmann says. The milk is also tested again once it arrives at the plant, Valenzuela says. 

“The milk is not unloaded at the plant until that test comes back negative,” Semler says. If the test is positive for contaminants, “the farmer just bought himself a load of milk,” Semler says, noting that the milk will be returned to the farm. 

If the test is negative (meaning, it doesn’t have contaminants), the milk will be transferred into the processing facility’s raw milk holding tanks, Beckman says. “The entirety of this process is highly regulated by the USDA and Food and Drug Administration Grade A Pasteurized Milk Ordinance, and is typically overseen locally by state departments of agriculture,” Beckman says. 

Pasteurization comes next 

Pasteurization is a process that involves heating food products (in this case, milk) to a specific temperature for a certain amount of time to kill off bacteria and extend the shelf life of the product. 

“Pasteurization does not impact the nutritional properties of milk but does ensure milk safety by killing bacteria,” Nichols says. “This is similar to cooking meat before consuming it.” Even if bird flu were in commercial milk, pasteurization would inactivate the virus, says infectious disease expert Amesh A. Adalja, MD, senior scholar at the Johns Hopkins Center for Health Security. 

The milk is separated after that 

The milk can then be separated depending on which dairy products it will be used to create, including fluid milk, cheese, and yogurt.

For fluid milk, the cream is usually removed and then added back in at a certain concentration, depending on whether the milk will be skim, 1%, 2%, or full-fat, Wiedmann says. From there, the milk will be homogenized, which is the process of forcing milk under high pressure through a valve that breaks up fat globules to a size that they will not stick together, creating a smooth liquid, Nichols says. “This is done for practical purposes to prevent cream from rising to the top of milk,” she explains, noting that homogenization does not affect the nutrition or quality of the product. Some milk will then be fortified with extra vitamins, minerals, protein, or flavors, Nichols says.

From there, the milk is bottled

There are more quality control tests done before the milk is bottled, Nichols says. It’s then bottled and shipped to retailers in refrigerated trucks. The whole timeline from cow to the store is short. “It usually takes about two days from the farm to the shelf,” Toledo says. 

Wiedmann stresses that processed milk is tightly regulated and safe. “It’s probably one of the safest products in the U.S. that you can have,” he says.