What Is pasteurization? history, methods, and how It works

Pasteurization has saved countless lives since Louis Pasteur introduced it in the 1860s. With the raw milk debate more heated than ever in 2026, here's what pasteurization actually does, how it works, and why the science behind it has never been stronger.

What Is pasteurization?

Pasteurization is the process of heating a food or beverage to a specific temperature for a defined period of time to destroy harmful bacteria, viruses, and other pathogens, without fully sterilizing the product or significantly altering its flavor and nutritional value.

The process is named after French scientist Louis Pasteur, who first demonstrated it in the 1860s. Today, pasteurization is required by law for milk sold in interstate commerce in the United States, and is applied to a wide range of products including juice, eggs, beer, wine, canned goods, honey, and some deli meats.

It is one of the most consequential food safety innovations in history, and in 2026, it is more relevant than ever. The ongoing debate over raw milk, the H5N1 bird flu outbreak in U.S. dairy cattle, and shifting federal policy under HHS Secretary Robert F. Kennedy Jr. have pushed pasteurization back into the national conversation in ways not seen in decades.

Louis Pasteur and the invention of pasteurization

Louis Pasteur (December 27, 1822 - September 28, 1895) was a French biologist, microbiologist, and chemist whose contributions to science changed the world. Most people associate him with pasteurization, but it was his work on germ theory that made everything else possible.

Disproving spontaneous generation

Before Pasteur's landmark research, the scientific community widely accepted the theory of spontaneous generation: the idea that microorganisms could arise on their own from nonliving matter. Pasteur's experiments with microbial fermentation in the 1850s and 1860s demolished this theory. Using sterilized, sealed flasks, he showed that microorganisms only developed when contamination was introduced from the outside. Without contamination, nothing grew.

This was the foundation of germ theory: the now-accepted understanding that diseases are caused by specific microorganisms, not by mystical spontaneous processes. Pasteur's evidence convinced the European and American scientific communities, and from that point on, the focus of medicine shifted toward preventing pathogens from entering the human body in the first place.

From wine to milk: The first pasteurization

Pasteur's experiments with fermentation led directly to a practical discovery. He found that bacteria were responsible for souring wine into vinegar, and that heating wine to between 60 and 100°C killed those bacteria without ruining the wine. He completed the first successful pasteurization test on April 20, 1862, eventually patenting the method.

The process was quickly applied to beer, juice, eggs, and most famously, milk. By killing most yeasts and molds without causing a phase change in the product, pasteurization extended shelf life while preserving flavor and nutritional quality. The food safety implications were enormous.

The four main methods of pasteurization

Since Pasteur's original discovery, food scientists have developed several methods of pasteurization, each optimized for different products, shelf life requirements, and processing needs.

Traditional pasteurization methods

• Vat pasteurization is the original method, still used for making starter cultures in cheese, yogurt, and buttermilk production. It heats liquid milk in a large tank to 145°F for at least 30 minutes, then cools it.
• High-temperature short-time (HTST) pasteurization is the most common method in the United States today. It uses metal plates and hot water to raise temperatures to at least 161°F for no less than 15 seconds, followed by rapid cooling, producing a refrigerated shelf life of approximately two weeks.
• Higher heat shorter time (HHST) pasteurization is similar to HTST but uses various combinations of higher temperatures and shorter durations, offering flexibility for different products.
• Ultra pasteurization (UP) heats liquids to at least 280°F for 1-2 seconds, extending refrigerated shelf life to approximately three months.

FDA recognized pasteurization temperature and time combinations

The following are the FDA-approved time and temperature combinations for milk pasteurization, as defined in the Pasteurized Milk Ordinance (PMO):

Source: International Dairy Foods Association (IDFA)

Newer pasteurization technologies

Beyond traditional heat-based methods, newer technologies extend shelf life, better preserve nutrients, and reduce the sensory impact of heating:

• Ultra-high-temperature (UHT) pasteurization, also known as aseptic processing, heats liquids with commercially sterile equipment and seals them in hermetically sealed packaging, producing shelf-stable products that don't require refrigeration until opened.
• Microwave volumetric heating (MVH) pasteurization uses microwaves to heat liquids, suspensions, or semi-solids continuously, delivering energy evenly throughout the product for gentler, shorter heating that better preserves heat-sensitive nutrients.
• Low temperature, short time (LTST) pasteurization sprays fine droplets in a chamber heated just below standard pasteurization temperatures for a few thousandths of a second, extending shelf life to 50 days or more while minimizing flavor changes.
• High-pressure processing (HPP) is an emerging non-thermal technique that uses pressure rather than heat to inactivate pathogens, preserving flavor and nutrients more effectively than conventional pasteurization. Its use in dairy products is growing rapidly.

The raw milk debate in 2026

Pasteurization has been uncontroversial for most of its 160-year history. That changed significantly in 2024 and 2025. A combination of factors, including an H5N1 bird flu outbreak in U.S. dairy herds, growing political opposition to food safety regulations, and the rise of a health freedom movement around raw dairy, has made pasteurization one of the most debated food safety topics in the country.

The H5N1 factor

In March 2024, the USDA, FDA, and CDC confirmed that highly pathogenic avian influenza (HPAI) H5N1 had been detected in U.S. dairy cattle for the first time, eventually spreading to herds in at least 19 states. The virus was found in raw milk from infected cows, raising immediate public health concerns.

The good news: pasteurization works against H5N1. The FDA tested 464 pasteurized dairy products including milk, cheese, butter, and ice cream, and found zero viable H5N1 virus in any of them. A joint FDA and USDA study published in 2024 confirmed that standard HTST pasteurization completely inactivated the virus. A 2025 study published in Nature Communications further confirmed efficient inactivation across all tested pasteurization conditions.

The political dimension

HHS Secretary Robert F. Kennedy Jr. has been a vocal critic of what he calls the FDA's aggressive suppression of raw milk, and has signaled interest in expanding access to unpasteurized dairy products. In April 2025, the FDA suspended oversight of the labs that conduct safety and quality testing on the nation's milk supply, a move that drew concern from food safety researchers and public health officials.

As of mid-2026, some 30 states allow raw milk sales in some form, and a dozen states have laws pending that would further expand access. Raw milk sales were reported to have risen 65% in 2024. The scientific consensus, however, has not shifted: the CDC and FDA continue to affirm that pasteurized milk is significantly safer than raw milk.

What the science says: busting raw milk myths

The FDA has published an official page debunking common raw milk myths. Here's what the evidence shows:

• Myth  Pasteurization causes lactose intolerance and allergic reactions. The FDA says this is false. Pasteurization does not alter lactose content or the proteins that trigger allergic reactions.
• Myth  Raw milk kills dangerous pathogens by itself. It does not. Raw milk can and does carry Salmonella, E. coli, Listeria, Campylobacter, and H5N1.
• Myth  Pasteurization significantly reduces milk's nutritional value. Multiple studies confirm it does not. The FDA states pasteurization does not meaningfully change milk's vitamins, minerals, or protein content.
  

• Fact  The risk of listeriosis from raw milk is 156 times higher than from pasteurized milk, according to Virginia Tech research published in 2024.
• Fact  Pasteurization kills H5N1 bird flu virus. FDA testing of 464 pasteurized dairy products in 2024 found zero viable H5N1 in any sample.
• Fact  Pasteurization saves lives. After NYC mandated milk pasteurization in 1910, childhood deaths from contaminated milk dropped dramatically. By 1973, the federal government required pasteurization of all milk in interstate commerce.

The legacy of Louis Pasteur

For his proof of germ theory, his discovery of microbial fermentation, and his invention of pasteurization, Louis Pasteur was a French national hero by age 55. His name is a household word around the world more than 130 years after his death.

Pasteur's work didn't stop at food safety. He also developed vaccines for anthrax and rabies, laying the groundwork for the entire field of immunology. His contributions rank among history's greatest scientific achievements. The UNESCO/Institut Pasteur Medal, created on the centenary of his death, is awarded every two years "in recognition of outstanding research contributing to a beneficial impact on human health."

In 2026, as debates about raw milk, food safety regulation, and public health institutions play out in real time, Pasteur's core insight is worth remembering: invisible microorganisms cause disease, and we have the tools to stop them. Pasteurization is 160 years old and still doing its job.

For food service operators, the lesson is practical. Maintaining the cold chain and proper temperature controls throughout storage and handling is what keeps pasteurization's protection intact. The heat treatment at the processing facility is only as good as the refrigeration that follows it.

Frequently Asked Questions

What is pasteurization?

Pasteurization is the process of heating a food or beverage to a specific temperature for a set period of time to kill harmful bacteria, viruses, and other pathogens. It was invented by French scientist Louis Pasteur in the 1860s and is now required by law for milk sold in interstate commerce in the United States.

What foods are pasteurized?

The most commonly pasteurized foods include milk and dairy products, fruit juices, eggs, beer, wine, canned goods, honey, flour, and some deli meats. In the U.S., all milk sold across state lines must be pasteurized by federal law. Many products in the refrigerated section of a grocery store, including liquid eggs and prepared juices, are also pasteurized.

Does pasteurization kill all bacteria?

No. Pasteurization kills most harmful pathogens including Salmonella, E. coli, Listeria, and H5N1 bird flu virus, but it is not sterilization. Some heat-resistant bacteria and spores can survive. This is why pasteurized products still require refrigeration and have a finite shelf life.

What is the difference between pasteurization and sterilization?

Pasteurization uses moderate heat to kill most harmful pathogens while preserving flavor and nutritional quality. Sterilization uses much higher heat to eliminate all microorganisms including heat-resistant spores, but can alter taste and nutrients. Canned goods are sterilized; milk and juice are pasteurized.

Is raw milk safer than pasteurized milk?

No. The CDC and FDA consistently affirm that raw milk is significantly less safe than pasteurized milk. Raw milk can carry dangerous pathogens including Salmonella, E. coli, Listeria, and H5N1 bird flu virus. The risk of contracting listeriosis from raw milk is 156 times higher than from pasteurized milk.

Does pasteurization reduce the nutritional value of milk?

No. The FDA and CDC confirm that pasteurization does not meaningfully reduce milk's nutritional value, does not cause lactose intolerance or allergic reactions, and does not make milk less digestible. These are common raw milk myths that lack scientific support.

Does pasteurization kill H5N1 bird flu virus in milk?

Yes. Multiple studies including FDA and USDA research published in 2024 and 2025 confirmed that standard pasteurization effectively inactivates H5N1 in milk. The FDA tested 464 pasteurized dairy products and found zero viable H5N1 virus. Raw milk, however, has tested positive for the virus.