Cultured milk and pasteurized milk are not the same thing. Cultured milk refers to milk that has been fermented with bacteria, while pasteurized milk refers to milk that has been heat-treated to kill harmful germs. However, in practice, the two processes are closely linked: in the United States, commercially sold cultured milk products like yogurt, kefir, and cultured buttermilk are almost always made from milk that was pasteurized first, before the bacterial cultures were added.
What Pasteurization Actually Does
Pasteurization is a heat treatment designed to kill dangerous bacteria in raw milk. The most common method heats milk to 72°C (161°F) for 15 seconds, though slower methods hold it at 63°C (145°F) for 30 minutes. Both achieve the same goal: eliminating pathogens like Salmonella, E. coli, Listeria, and Campylobacter without significantly changing the milk’s nutritional profile. One study found that standard high-temperature pasteurization caused only about 1% breakdown of immunoglobulin G, a key immune protein in milk.
What Culturing Actually Does
Culturing is a completely separate process. Specific strains of lactic acid bacteria are added to milk, where they feed on lactose (milk sugar) and convert it into lactic acid. This drops the pH of the milk, making it acidic. That acidity thickens the milk, gives it a tangy flavor, and creates an environment hostile to many harmful microorganisms.
The organic acids produced during fermentation do offer some natural protection. Lactic and acetic acids interfere with the metabolism of pathogenic bacteria, damage their cell membranes, and can reduce or even eliminate populations of harmful organisms like Enterobacteriaceae. Some beneficial strains, particularly certain Lactobacillus species, produce antimicrobial compounds that actively inhibit pathogen growth.
But this protection has limits. Fermentation alone does not reliably kill every dangerous pathogen that might be present in raw milk. The FDA is explicit on this point: raw milk does not kill dangerous pathogens by itself, and products made from unpasteurized milk, including yogurt, are considered high-risk foods.
Why Commercial Cultured Milk Is Pasteurized First
Under the FDA’s Grade “A” Pasteurized Milk Ordinance, milk and milk products sold commercially must meet pasteurization standards. Cultured buttermilk, for example, must be made from cream that has been pasteurized before use. Yogurt must reach an initial pH of 4.80 or below at filling and is subject to the same pasteurization requirements for its base milk.
The standard production sequence works like this: raw milk is pasteurized to eliminate pathogens, then cooled to a temperature suitable for bacterial growth, and then the live cultures are added. This order matters. Pasteurizing after culturing would kill the beneficial bacteria you just introduced. The goal is a product that starts clean (thanks to pasteurization) and then gains its flavor, texture, and probiotic benefits from controlled fermentation.
Products with higher fat content (10% or above) or higher total solids (18% or above) must be pasteurized at temperatures 3°C (5°F) higher than the standard chart to ensure safety.
Does Culturing Make Pasteurization Unnecessary?
No. While the low pH environment created by fermentation does suppress many pathogens, it is not a substitute for pasteurization. The FDA lists yogurt made from unpasteurized milk, unpasteurized soft and hard cheeses, and unpasteurized cream as high-risk foods. Pregnant women, young children, older adults, and people with weakened immune systems face the greatest danger from these products.
Some traditional food systems around the world rely on fermentation alone for safety, and research on spontaneous fermentation in rural communities has shown considerable reductions in harmful bacteria counts. But “considerable reduction” is not the same as reliable elimination. Pasteurization achieves a consistent kill of pathogens that fermentation alone cannot guarantee.
What About Live Cultures After Processing?
One reason cultured milk is not pasteurized after fermentation is to preserve the live bacteria that provide health benefits. Fermented dairy products, particularly yogurt, have been shown to ease symptoms of lactose intolerance. The bacteria in yogurt (typically Streptococcus thermophilus and Lactobacillus bulgaricus at concentrations of 10 million colony-forming units per milliliter or higher) release an enzyme in your intestine that helps break down lactose.
Some manufacturers do use high-pressure processing as a final step to extend shelf life without traditional heat. Research shows this can reduce probiotic counts modestly, by about 0.5 to 1.2 log units, at pressures up to 300 MPa while keeping cultures above minimum required levels. Push the pressure to 400 MPa, though, and probiotic counts drop below acceptable thresholds. This is why you will sometimes see “contains live and active cultures” on a label and sometimes not. If a cultured product has been heat-treated or heavily processed after fermentation, those beneficial bacteria may no longer be alive.
How to Tell What You’re Buying
If you are buying cultured milk from a grocery store in the U.S., the base milk was almost certainly pasteurized before culturing. The label will typically say “cultured pasteurized milk” or list pasteurized milk as the first ingredient. If you see “contains live and active cultures,” the product was not heat-treated after fermentation, meaning the beneficial bacteria are still viable.
At farmers’ markets or from small producers, the rules vary by state. Some states allow the sale of raw milk and raw milk products, including cultured ones. If the label says “raw” or does not mention pasteurization, the milk was not heat-treated before or after culturing. These products carry a higher risk of containing harmful bacteria regardless of the fermentation process.
The short version: cultured and pasteurized describe two different things done to milk for two different reasons. But in commercial production, you almost always get both. The milk is pasteurized for safety, then cultured for flavor, texture, and the benefits of live bacteria.