Pasteurized milk is milk that has been heated to a specific temperature for a set period of time to kill harmful bacteria, then rapidly cooled. Nearly all milk sold in grocery stores in the United States is pasteurized. The process makes milk safer to drink without significantly changing its taste, appearance, or nutritional value.
How Pasteurization Works
Pasteurization uses heat to destroy disease-causing microorganisms in milk. The most common method used in commercial dairy processing is called High-Temperature Short-Time (HTST) pasteurization: milk is heated to 161°F (72°C) for just 15 seconds, then quickly cooled. This is the method behind most of the fresh milk in your refrigerator.
An older approach, sometimes called holder pasteurization, heats milk to a lower temperature of about 145°F (62.5°C) but holds it there for 30 minutes. This method is slower and used less often for commercial milk, though it remains the standard process for pasteurizing donated human breast milk in hospitals. A third option, ultra-high temperature (UHT) processing, heats milk well above standard pasteurization temperatures. UHT milk can be stored at room temperature in sealed containers for months, which is why you’ll sometimes find shelf-stable milk boxes in the grocery aisle rather than the refrigerated section.
To confirm that pasteurization worked, dairy plants test for a naturally occurring enzyme in milk that breaks down at the same temperatures as harmful bacteria. If the enzyme is still active, the milk wasn’t heated enough. This quick test acts as a built-in quality check on every batch.
What Pasteurization Kills
Raw milk can carry bacteria responsible for serious foodborne illnesses, including Salmonella, E. coli O157:H7, Campylobacter, and Listeria. Before pasteurization became widespread, milk was also a common vehicle for tuberculosis and brucellosis. The original goal of the process, developed by Louis Pasteur in 1864, was specifically to inactivate the bacterium that causes tuberculosis in humans.
Pasteurization eliminates the vast majority of these pathogens. It does not sterilize milk completely. Some heat-resistant bacteria, like certain species of Staphylococcus and Bacillus, can survive the process in small numbers. Under normal refrigeration, these survivors rarely cause problems. The bigger risk with pasteurized milk is contamination after the fact, during packaging or handling, which is why proper refrigeration and attention to expiration dates still matter.
Raw Milk vs. Pasteurized Milk Safety
The safety gap between raw and pasteurized milk is stark. From 1987 to 2010, the FDA documented at least 133 outbreaks linked to raw milk and raw milk products in the United States, resulting in 2,659 illnesses, 269 hospitalizations, 3 deaths, 6 stillbirths, and 2 miscarriages. What makes those numbers especially striking is that raw milk accounts for less than 1% of all milk consumed in the country. Children are particularly vulnerable to the pathogens found in raw milk.
When outbreaks have been traced to pasteurized milk, investigators have typically found that the milk was contaminated after pasteurization, often by contact with raw milk or unclean equipment. The pasteurization process itself, when done correctly, is remarkably effective.
Nutritional Impact
One of the most common concerns about pasteurization is whether it strips milk of its nutrients. The short answer: the losses are real but modest for most vitamins, and the major nutritional benefits of milk remain intact.
A large meta-analysis of existing studies found that pasteurization causes statistically significant decreases in vitamins B1, B2, C, and folate. Vitamins B12 and E also showed declines. On the other hand, vitamin A levels actually increased slightly after pasteurization. Vitamin B6 levels were not significantly affected. The minerals in milk, including calcium, phosphorus, and potassium, are heat-stable and come through pasteurization essentially unchanged.
In practical terms, milk is not a major dietary source of vitamin C or folate to begin with. The nutrients people rely on milk for, particularly calcium, protein, and vitamin D (which is added through fortification after pasteurization), are unaffected by the process.
Pasteurization vs. Homogenization
These two processes are often confused, but they do completely different things. Pasteurization is a heat treatment that kills bacteria. Homogenization is a mechanical process that breaks fat globules into smaller, uniform particles so the cream doesn’t separate and float to the top. Homogenization involves no heat, no chemicals, and no additives. It simply changes the physical structure of the fat so milk stays smooth and consistent from the first pour to the last. Most commercial milk is both pasteurized and homogenized, but the two steps are independent of each other.
Lactose Intolerance and Allergies
Pasteurization does not change the lactose content of milk. If you’re lactose intolerant, pasteurized and raw milk will cause the same digestive symptoms. The claim that raw milk is easier to digest for lactose-intolerant people has not been supported by controlled studies.
Similarly, the proteins in milk that trigger allergic reactions, primarily casein and whey, are not significantly altered by standard pasteurization temperatures. People with a true milk protein allergy will react to both raw and pasteurized milk. The allergy is to the milk itself, not to anything the processing does to it.
How Pasteurized Milk Is Labeled
In the United States, the FDA’s Grade “A” Pasteurized Milk Ordinance governs how milk is labeled and sold. Pasteurized milk containers must display the name and location (or permit number) of the processing plant, along with a “Grade A” designation. The label must also specify whether the milk has been pasteurized, ultra-pasteurized, or aseptically processed. Misleading labels or descriptive terms that could confuse consumers are prohibited under federal guidelines.
If a carton of milk in a U.S. grocery store doesn’t say “raw” on it, it has been pasteurized. The process is so standard that many people drink pasteurized milk their entire lives without ever thinking about what the word means.