Debate over raw milk has been heating up in recent years, and especially the past few months. Raw milk sales are rising, despite emerging concerns over live avian flu in unpasteurized dairy, and it’s increasingly a political talking point.
Advocates of raw milk consumption claim that pasteurization reduces milk’s nutritional value and removes health benefits, despite lack of scientific support for the vast majority of these claims. At the same time, experts agree that forgoing pasteurization carries unnecessary health risks.
What is pasteurization?
In short: pasteurization “is a combination of temperature and time,” says Dennis D’Amico, an associate professor of food science who focuses on dairy safety and production at the University of Connecticut. The hotter the pasteurization temperature, the shorter the amount of time needed to kill off pathogens, and the lower the temperature the longer it takes. There are a few approved heat/time combinations in the U.S., but the most common method used for store bought, refrigerated milk is 72 degrees Celsius (161.6 degrees Fahrenheit) for 15 seconds, says D’Amico. Raw milk is simply unpasteurized.
Even before widespread pasteurization and regulations, many people would boil milk at home before drinking it to ensure its safety, notes Kerry Kaylegian, a dairy food scientist and associate research professor at Penn State University. Boiling is an even more aggressive form of heating than pasteurization, which was developed to kill pathogens while minimizing changes to milk’s flavor and composition, says John Lucey, a food science professor at the University of Wisconsin, Madison and director of the university’s Center for Dairy Research. “Boiling is a very substantial heat treatment whereas pasteurization is much gentler,” he notes. In parts of the world today where pasteurization isn’t well-regulated or universally adopted, boiling remains commonplace.
Why do we pasteurize? A brief bovine history
Pasteurization goes back to the mid-1800’s. French chemist and microbiologist, Louis Pasteur discovered that heating beer to a certain temperature for a certain amount of time prevents the growth of undesirable microbes, which spoil the batch. He sought patents for pasteurization, initially, as a means to improve the shelf life of beer and wine.
Then, a German agricultural chemist, Franz von Soxhlet, thought to apply the same process to milk in 1886. At the time, drinking dairy was often dangerous–especially for infants and children, who were frequently bottle fed cow’s milk. Harmful pathogens were commonly present in the milk supply in both Europe and the U.S. and pasteurization emerged as a way to eliminate them–particularly bovine tuberculosis, which caused waves of human infections and deaths throughout the 19th and early 20th centuries.
Milk pasteurization came on the scene just as germ theory was becoming better understood and accepted, and its adoption, along with other societal shifts, led to about a 50% decline in infant mortality–a clear public health win. Yet some detractors at the time resisted the practice, especially in the U.S. where uptake was slower. They made claims about flavor and nutrient content, similar to those still made today.
In lieu of pasteurization, these naysayers initially tried to make other aspects of dairying more sanitary–in acknowledgement that microbes were, in fact, killing people. They argued that improving farm and facility conditions, and checking for cow diseases would reduce risk, rendering pasteurization unnecessary and even that pasteurization would make farmers lax in their animal upkeep, says John Lucey, a food science professor at the University of Wisconsin, Madison and director of the Center for Dairy Research. But focusing on cleanliness and animal health alone proved a far more difficult and a less reliable way to manage safety than pasteurization, Lucey says. Animals can secrete microbes in their milk long before they appear sick, even the most diligent standard cleaning doesn’t eliminate everything, and intermittent testing does nothing to prevent what falls through the cracks.
In the early 1900’s U.S. municipalities began to require pasteurization in a piecemeal fashion. And in 1924, the federal government issued the Pasteurized Milk Ordinance (PMO), which established a national program for pasteurization. It’s a long, complicated document because, in addition to tackling time and temperature requirements, the ordinance also details equipment design, maintenance, and sanitation strategies for improving dairy safety–rolling both approaches to dairy safety into one policy. The PMO doesn’t require that all milk sold be pasteurized, but it sets standards for Grade A milk. The legality of raw milk is determined at the state level, and the majority of states allow some form of raw milk sale. As of 1973, federal law prohibits the sale of unpasteurized milk across state lines.
How risky is raw milk?
Drinking raw milk carries “a significant risk,” says Lucey. It’s not that any amount of raw milk consumption guarantees illness, but every glass of raw milk is a small gamble. Prior to widespread pasteurization, milk was responsible for a quarter of all food and waterborne disease outbreaks, according to FDA data.
Contracting tuberculosis is no longer a primary concern for milk drinkers (largely thanks to pasteurization, USDA surveillance, and an ongoing disease eradication program). Yet other pathogens have become common in raw milk including listeria, some especially dangerous strains of E. coli, salmonella, campylobacter, and toxin-producing Staphylococcus aureus, says D’Amico.
As avian influenza continues to spread among dairy herds, milk now also frequently tests positive for the virus. Though there haven’t yet been confirmed human cases of bird flu acquired through raw milk consumption, there have been reports of cats becoming ill and dying after being fed raw milk from sick cows.
[ Related: Can we prevent a bird flu pandemic in humans? ]
The presence of pathogens in dairy is not necessarily a function of the scale or type of farming facility, says Kaylegian. Both small and large processors can produce contaminated and uncontaminated milk, she emphasizes. Microbes come from the soil, the animals, the human workers, equipment, containers, and even the air. “We find bacteria everywhere…no farm is a sterile environment,” says Lucey. Some assessments find that a third of raw milk samples contain pathogens, according to a 2015 review authored by Lucey.
Thresholds for detection and for human infection can differ, and different people have different abilities to fight off infection, so that doesn’t mean one third of raw milk will make people sick. Yet it means illness is an ever-present possibility. Calculating exact risk and incidence rate is difficult, says Lucey, because with a fresh product that gets consumed or spoils within a matter of days like raw milk, confirming contamination or the source of an outbreak after the fact is often impossible. Recalls are contingent on chance, he adds–where testing is lucky enough to capture evidence that a facility or farm was the origin of someone’s illness days or weeks after the fact.
But here are some numbers anyway. About 1% of Americans–or around 3.3 million people report consuming raw milk on a weekly basis, per a 2022 FDA report. One 2017 analysis found that dairy causes an average of 760 confirmed cases of illness per year, and that unpasteurized dairy constituted 96% of those cases. Or, in other words, that raw milk was 840 times more likely to cause illness and 45 times more likely to lead to hospitalization.
Now, 96% of 760 is about 730. 730 out of 3.3 million is not a huge number, it amounts to a 1 in ~4,520 chance of falling ill from consuming raw milk. Yet an important caveat is that those confirmed cases are likely a major undercount, says Lucey: “It’s the tip of the iceberg.” In addition to the aforementioned difficulty of confirming milk-related outbreaks, many people don’t report illness or don’t realize it may have stemmed from drinking raw milk. One analysis of 10-years worth of food poisoning cases in Minnesota estimated that about 17% of people who drink raw milk may become ill from it.
Healthy adults might just suffer a few days of gastrointestinal distress from milk-borne illness. But children, people over 65, and those who are pregnant or immunocompromised are at much higher risk of severe consequences from the pathogens often present in raw milk–including death, long-term kidney damage, and pregnancy loss. And pregnant and very young people are especially encouraged to drink milk for its calcium content, notes Lucey.
In Pennsylvania, where Kaylegian lives and works, selling raw milk is legal via a licensing process. It’s also a state where illness outbreaks due to raw milk happen often. “The more raw milk consumed, the more frequent the outbreaks are. And they’re constant,” Kaylegian says. “Every couple of months, somebody else is getting sick…or pathogens have been found, and there’s another recall.”
In 2024, there’ve been 10 recalls related to raw dairy products so far, according to the Center for Dairy Research. At the end of 2023, one salmonella outbreak linked to unpasteurized dairy from a California farm resulted in at least 171 sick people and 22 hospitalizations. The company responsible for this outbreak, Raw Farm LLC (formerly Organic Pastures Dairy Company), is headed by Mark McAfee, who also founded and chairs the Raw Milk Institute. This non-profit organization offers guidance to farms and promotes standards intended to ostensibly lower the risk of raw milk production. Yet, despite the Raw Milk Institute’s claims of “clean, safe raw milk,” the CEO’s own farm has been at the center of 11 illness outbreaks and subject to as many product recalls since 2006. “In most other sectors, they would be long-gone and closed out, and they’re still producing product,” says Lucey.
When it comes to drinking raw milk, “I’m one of those folks that thinks the risk is not worth it,” says D’Amico. Both Lucey and Kaylegian agree.
Cheese, however, is a slightly different story. Cheesemaking involves salt, acid, drying, and aging–all processes which kill off a meaningful portion of harmful microbes, says D’Amico. Hard cheeses, aged 60 days or more that are made with raw milk are relatively safe, even if the milk was initially contaminated, he notes, and he happily enjoys them. Soft and fresh cheeses made from raw milk, on the other hand, are “much less safe,” adds D’Amico. “I wouldn’t eat those.”
But is raw milk good for you?
For many, the question of risk is only half the conversation when it comes to raw milk. Pasteurization’s detractors promote the idea that unpasteurized dairy carries big health benefits over pasteurized milk, and fashion raw milk as a superfood. Yet all of the experts Popular Science spoke with note that these claims are not well-supported by scientific evidence, and that there is no scientific consensus backing any particular benefits to raw milk.
Some of the most popular talking points are that unpasteurized milk is more nutritious, reduces lactose intolerance, aids digestion, reduces asthma and allergy risks, promotes a healthy immune system, and boosts the gut microbiome. Most of these claims can be traced back to particular misunderstandings or misinterpretations of science, notes Lucey.
Pasteurization does affect the amount of some of the vitamins in milk. Some nutrients, like vitamin C, are heat-sensitive. Pasteurization might reduce vitamin C content by about 20% in milk, says D’Amico. But critically: vitamin C is present in milk only in very small quantities, he adds. Milk is not a major source of any heat-sensitive nutrients (with the possible exception of riboflavin, which is widely available in other foods). Plus, these vitamin losses from pasteurization are far exceeded by the losses that result from storing milk in clear glass bottles, which are open to light, says Lucey. None of the proteins, fats, or minerals in milk are significantly degraded by standard pasteurization, he adds. However, the way cows are fed does influence milk’s nutrient content. Grass-fed cows produce milk with a higher omega-3 content, according to one 2018 study and multiple, older analyses. The benefits of pasture-feeding shouldn’t be mistaken for downsides of pasteurization.
Raw milk also has nothing to do with lactose intolerance, says Kaylegian. That’s determined solely by whether or not your own body produces lactase, the enzyme responsible for breaking down lactose. Milk itself does not naturally contain any lactase, and raw milk does not help with dairy digestion, she says. It also doesn’t contain any probiotics.
Some correlative studies performed in Europe have found that people who consume raw or farm milk have a reduced risk of disorders like asthma. However, Lucey points out that these studies only found a difference between raw milk and the ultra-high temperature treated, sterilized, shelf-stable milk common across Europe–not pasteurized milk according to U.S. standards.
In some cases, this research also conflates boiled farm milk with raw milk. And most studies fail to separate the effects of the traditional farming ways with drinking unpasteurized dairy. Children who grow up on farms, with lots of animal contact and outdoor exposure are less likely to end up with allergies or asthma. Yet data doesn’t indicate raw milk plays a role. Both Mennonite and Amish children have high rates of raw milk consumption. However, Mennonites have significantly higher asthma rates than Amish children, according to a 2018 study. The difference likely comes down to lifestyle, says Lucey. Mennonite children, he notes, have less contact with animals.
Science is not set in stone. New research can bring new data to light, and it’s possible that down the line, reviews and meta analyses may eventually reveal some small benefit to raw milk consumption. But meanwhile the potential danger, especially for children, are well-established. When it comes to milk, we have an easy, well-proven way of mitigating the harm without any proven downsides. Why not use it?
This story is part of Popular Science’s Ask Us Anything series, where we answer your most outlandish, mind-burning questions, from the ordinary to the off-the-wall. Have something you’ve always wanted to know? Ask us.
