Raw Milk: Unpasteurized Science

Few food safety topics generate more heat than raw milk. On one side, people who view unpasteurized milk as a natural, nutritionally superior food with a long traditional history. On the other, public health agencies pointing to outbreak data and pathogen risk. Both sides are talking past each other partly because they’re measuring different things.

Here’s what the science actually says: on pasteurization, on the health benefit claims, and on the genuine risk.

What Pasteurization Is and How It Works

Pasteurization was developed by Louis Pasteur in the 1860s to kill spoilage organisms in wine and beer. The core principle: heat food to a temperature that kills pathogens without completely altering its character.

For milk, there are several commercial pasteurization methods. The two most common are:

HTST (High Temperature, Short Time): 161°F / 71.7°C for 15 seconds. This is the standard for most commercial milk. It kills pathogens while minimally affecting taste and nutritional composition. Milk is still perishable after HTST and requires refrigeration.

UHT (Ultra-High Temperature): 280°F / 138°C for 2 to 4 seconds. This produces shelf-stable milk that can sit unrefrigerated for months. It has a more “cooked” flavor that’s noticeable to some palates. It’s extremely common in Europe and increasingly available in the US.

Vat pasteurization (low-temp): 145°F / 63°C for 30 minutes. A slower method sometimes used by smaller operations. Still effective at killing pathogens.

The mechanism in all cases is protein denaturation. The heat disrupts the three-dimensional structure of proteins in bacterial cell walls and enzymes, killing the cells. This is the same process that changes the texture of a cooked egg white, applied to bacteria. The denaturation article explains the underlying chemistry.

The Health Claims: Examined One by One

Proponents of raw milk make several specific claims. Each deserves an honest look.

“Raw milk has beneficial enzymes that are destroyed by pasteurization”

True that enzymes are denatured by pasteurization. False that it matters.

The stomach is a highly acidic environment (pH 1.5 to 3.5 during active digestion). Proteins (including enzymes) are unfolded and broken down by both the acid and by pepsin, a stomach enzyme. The vast majority of ingested enzymes from any source (raw milk, raw vegetables, raw anything) are denatured and broken into amino acids before they reach the small intestine.

The claim that lactase in raw milk helps lactose-intolerant people digest it better has been tested directly. A 2014 study in the Annals of Family Medicine found no difference in lactose digestion symptoms between raw and pasteurized milk in self-identified lactose-intolerant adults.

“Pasteurization reduces the bioavailability of nutrients”

Some heat-sensitive vitamins, primarily vitamin C and some B vitamins, are reduced by pasteurization. The reduction is real but small (10 to 25 percent for the most heat-sensitive). Milk is not a significant source of vitamin C in most diets. Calcium, phosphorus, protein, and fat are essentially unaffected.

Multiple controlled studies comparing raw and pasteurized milk have found no meaningful difference in nutritional bioavailability for the nutrients milk is actually used for: calcium, protein, riboflavin, vitamin D (added, not affected by pasteurization), and vitamin A.

“Raw milk contains beneficial bacteria that improve gut health”

This claim requires distinguishing between “bacteria are present” (true) and “those bacteria survive and colonize your gut” (not demonstrated).

Raw milk does contain Lactobacillus and other bacteria associated with fermented dairy products. But milk straight from a cow also contains whatever microorganisms were on the udder, in the milking equipment, and in the environment. A 2018 analysis found that the dominant bacteria in raw milk are environmental contaminants from the dairy environment, not beneficial probiotic strains.

Commercial fermented dairy products (yogurt, kefir, aged cheese) deliver lactic acid bacteria in much higher, more controlled concentrations, in formats where those bacteria have already modified the substrate in beneficial ways.

“Raw milk tastes better”

This one is genuinely subjective, and for many people it’s true. Raw milk has a fuller, sometimes grassy flavor profile that comes from the fat structure and from microorganisms that haven’t been killed. UHT pasteurization does produce off-flavors. HTST pasteurization has minimal flavor impact, but raw milk from a farm where cows graze on varied pasture will taste different from commodity pasteurized milk from grain-fed confinement cows. That flavor difference is mostly about diet and freshness, not pasteurization.

The Actual Pathogen Risk

The CDC publishes data on dairy-related outbreaks. The numbers are consistent.

Raw milk products are responsible for a disproportionate share of dairy-related foodborne illness, given how small a fraction of total milk consumption they represent. The CDC’s analysis found that raw milk was 150 times more likely to cause illness and 13 times more likely to cause hospitalization than pasteurized milk.

Between 2009 and 2014, raw milk and raw milk products caused 81 percent of all dairy-related illness outbreaks in the US, while representing an estimated 1 to 3 percent of milk consumed.

The pathogens responsible for these outbreaks include:

• Campylobacter: The most common bacterial cause of diarrheal illness in the US. Common in cattle. Causes bloody diarrhea, abdominal cramps, fever. Most people recover in 1 to 2 weeks. Can trigger reactive arthritis and Guillain-Barre syndrome in rare cases.
• Salmonella: Causes gastroenteritis. Usually self-limiting in healthy adults, but dangerous for vulnerable populations.
• E. coli O157:H7: Produces Shiga toxin. In some cases, especially in children, causes hemolytic uremic syndrome (HUS), which can lead to kidney failure.
• Listeria monocytogenes: Can grow at refrigerator temperatures. Particularly dangerous in pregnancy, where it can cause miscarriage, stillbirth, and neonatal illness.

The critical point about E. coli O157:H7 and Listeria is that these bacteria can be present in milk from healthy, apparently clean cattle. Contamination isn’t a sign of poor farm management. It’s a function of the biology of cattle and their environment. Even well-managed raw milk operations carry these risks. Testing raw milk before sale reduces but doesn’t eliminate the risk, because contamination can occur after testing.

Honest Risk Framing

Adults are allowed to make choices that involve risk. You can choose to ride motorcycles, free climb rocks, eat rare steak, or drink raw milk. These are legal choices in many jurisdictions, and the argument that adults should control their own food choices is coherent.

The honest framing for raw milk is:

1. The health benefit claims are largely not supported by evidence
2. The pathogen risk is real, documented, and significantly higher than pasteurized milk
3. The risk falls hardest on people who can’t make the choice themselves: children, fetuses, immunocompromised people
4. “The farm I buy from is clean and tested” doesn’t eliminate the risk. It reduces it somewhat, but testing can’t guarantee every batch is free of dangerous pathogens.

The comparison to pasteurization being controversial when it was introduced is historically accurate. In the 1890s and early 1900s, pasteurization was opposed by some dairy farmers and some consumers on similar grounds. The infant mortality data from milk-borne illness in that era is what drove its adoption. Tuberculosis, typhoid fever, and scarlet fever spread extensively through raw milk before pasteurization became standard.

That historical context doesn’t tell you what you should personally choose. It does tell you that the risk is real enough that it changed public health policy across the developed world. The science since then hasn’t changed that assessment.