Pasteurization is important because it eliminates dangerous bacteria from milk and other beverages while keeping their nutritional value largely intact. Unpasteurized dairy products cause 840 times more illnesses than pasteurized ones, according to CDC data, despite being consumed by only a tiny fraction of the population. That single statistic captures why this process, developed in the 1800s, remains one of the most effective food safety measures in the modern world.
How Heat Kills Harmful Bacteria
Pasteurization works by using heat to destroy the internal structure of bacteria and other pathogens. When milk is heated above 60°C (140°F), the proteins inside microorganisms begin to unfold, a process called denaturation. These proteins lose their original shape, which means they can no longer function. The unfolded proteins clump together irreversibly, effectively killing the organism. The same process also deactivates certain enzymes naturally present in raw milk.
This is not sterilization. Pasteurization doesn’t kill every microorganism in milk. Instead, it targets the specific temperature and time combination needed to destroy the most heat-resistant pathogen commonly found in milk, while preserving as much of the milk’s original character as possible.
Pathogens Found in Raw Milk
Raw milk can harbor a long list of bacteria that cause serious illness. The FDA identifies E. coli O157:H7, Salmonella, Campylobacter, Listeria, Staphylococcus aureus, and the bacteria responsible for tuberculosis (Mycobacterium tuberculosis) among the pathogens that have been found in unpasteurized milk. It also carries Coxiella burnetii, the organism that causes Q fever, a disease that can lead to chronic heart infections.
These aren’t theoretical risks. Between 2009 and 2014, unpasteurized milk and cheese, consumed by only about 3.2% and 1.6% of the U.S. population respectively, were responsible for 96% of all illnesses caused by contaminated dairy products. Put another way, people drinking raw milk faced 840 times the illness rate and 45 times the hospitalization rate compared to those consuming pasteurized products.
Standard Pasteurization Methods
The most common method used in commercial dairy processing is High-Temperature Short-Time (HTST) pasteurization. Milk flows continuously through a heat exchanger and is heated to at least 72°C (161°F) for 15 seconds. That brief exposure is enough to destroy the dangerous pathogens listed above. An older method, Low-Temperature Long-Time (LTLT) pasteurization, holds milk at 63°C (145°F) for 30 minutes and is still used by some smaller dairies.
Ultra-High Temperature (UHT) processing goes further, heating milk above 135°C (275°F) for just a few seconds. This kills virtually all microorganisms, not just pathogens, which is why UHT milk can sit unopened on a shelf at room temperature for months. Stored at refrigerator temperature (4°C), UHT milk lasts 34 to 36 weeks. Even at warmer room temperatures around 30°C, it holds for 16 to 20 weeks. Standard HTST pasteurized milk, by contrast, needs refrigeration and typically lasts two to three weeks.
What Pasteurization Does to Nutrients
One of the most persistent concerns about pasteurization is that it strips milk of its nutritional value. The FDA states directly that pasteurization kills pathogens “without any significant impact on milk nutritional quality.” The major nutrients people drink milk for, including protein, calcium, and fat, survive the process without meaningful losses.
Heat-sensitive vitamins do take a hit, but the losses are modest and largely limited to vitamins that milk isn’t a major dietary source of anyway. Research on holder pasteurization (the LTLT method) found that vitamin C dropped by about 36%, folate by 31%, and vitamin B6 by 15%. Those percentages sound significant in isolation, but most people get their vitamin C from fruits and vegetables, not milk. The core nutritional profile of pasteurized milk, the calcium, protein, vitamin D, and vitamin A that make it a dietary staple, remains essentially unchanged.
Heat does denature whey proteins in milk, causing them to unfold and interact with other proteins. This changes the milk’s physical properties slightly (it’s part of why pasteurized milk tastes a bit different from raw) but doesn’t reduce the protein’s nutritional value to your body. Your digestive system breaks proteins down into amino acids regardless of whether they arrive folded or unfolded.
Why Raw Milk Claims Don’t Hold Up
Advocates for raw milk often argue that pasteurization destroys beneficial enzymes like lipase and phosphatase that aid digestion. It’s true that heat inactivates these enzymes. But there’s no credible evidence that the enzymes naturally present in cow’s milk play a meaningful role in human digestion. Your body produces its own digestive enzymes in abundance. The loss of alkaline phosphatase in milk is actually used as a test to confirm pasteurization was successful, not because the enzyme matters nutritionally, but because its absence proves the milk reached a sufficient temperature.
Another common claim is that raw milk is safer when it comes from clean, grass-fed farms. While good farming practices reduce contamination risk, they cannot eliminate it. Bacteria like Campylobacter and E. coli can be present in healthy cows with no signs of illness, and even a single contamination event during milking can introduce pathogens. The CDC outbreak data makes clear that even in a country with modern farming standards, raw milk remains a significant source of foodborne illness.
Beyond Milk
Pasteurization isn’t limited to dairy. The same principle of applying controlled heat to destroy pathogens is used for fruit juices, egg products, beer, wine, and canned foods. After several outbreaks of E. coli and Salmonella linked to unpasteurized apple cider and orange juice in the 1990s, the FDA began requiring warning labels on unpasteurized juices. The logic is identical to milk: a brief, precisely controlled application of heat eliminates the organisms most likely to cause illness, with minimal effect on flavor or nutrition.
The simplicity of pasteurization is part of what makes it so important. It requires no chemical additives, no irradiation, and no genetic modification. It’s just heat, applied at the right temperature for the right duration, doing what it has done reliably for over 150 years.