You have seen the word printed on a milk carton, a juice bottle, and a carton of eggs, usually in small type near the expiration date. Lately it may have shown up somewhere less expected: the ingredient panel of a supplement that lists a "heat-treated" culture. So what is pasteurization, exactly? It is a heat process with a precise name, a specific inventor, and a history that starts with wine, not milk.

Once you know where the word came from and what it describes, the label language gets much easier to read.

In Google Trends data for the US over the past 7 days, rising searches tied to the seed term "pasteurization" were led by "when was pasteurization invented" (+250%), followed by "define pasteurization" (+130%), "pasteurization invented" (+60%), and "who invented pasteurization" (+50%). Among top searches, "milk pasteurization" scored 100, followed by "what is pasteurization" (86), "pasteurization process" (35), "pasteurization definition" (17), "louis pasteur pasteurization" (15), and "flash pasteurization" (6). A rising percentage shows growth in search interest compared with the prior period. Top scores are relative interest scaled so the top term equals 100; they are not search counts. The pattern is clear: people want the definition, the date, and the name behind it.

What is pasteurization? The definition

Start with the dictionary. Merriam-Webster defines pasteurization as partial sterilization of a substance, especially a liquid such as milk, at a temperature and for a period of exposure that destroys objectionable organisms without major chemical alteration of the substance. It lists a second, newer sense as well: the irradiation of food products.

Encyclopaedia Britannica puts it more briefly, describing pasteurization as a heat treatment that destroys disease-causing microorganisms in certain foods and beverages. The International Dairy Foods Association, a US dairy trade group, uses nearly the same wording: a process, named after the scientist Louis Pasteur, that applies heat to destroy pathogens in foods.

Read those three definitions side by side and two ideas repeat. First, pasteurization is about heat. Second, it is aimed at certain microorganisms, not at every living thing in the product. If you searched "define pasteurization" or "pasteurization definition," that is the short version: a controlled heat treatment named after Louis Pasteur.

Who invented pasteurization, and when?

The name tells you who. The story tells you it began with wine.

According to the Science History Institute, Pasteur's research turned toward fermentation in 1854, during his appointment in Lille. He went on to show that yeast, a living organism, was responsible for alcoholic fermentation. If you want the background on that process itself, our explainer on what fermentation is walks through it from the start.

The Institut Pasteur, the research foundation Pasteur established in Paris, says that in 1863 Napoleon III asked him to study the "diseases" of wine. Pasteur found that microbes were behind the spoilage and proposed heating the wine. The Science History Institute dates his finding that heat could stop wine spoilage to 1864, and the Institut Pasteur records that on 11 April 1865 he filed a patent for a process relating to the preservation of wines. Britannica summarizes the work this way: in the 1860s, Pasteur demonstrated that abnormal fermentation of wine and beer could be stopped by heating the beverages for a few minutes.

So if your search was "when was pasteurization invented," the documented answer is the mid-1860s, with 1864 as the year of the finding and 1865 as the year of the patent.

There is a fair footnote. The Institut Pasteur itself notes that heating wine was known before Pasteur. His contribution, it says, was turning the practice into a scientific process with a clear explanation behind it. That is why "louis pasteur pasteurization" is such a common pairing: the method carries his name because he explained why it worked.

How the word itself spread

The word came after the method. The Institut Pasteur says the term "pasteurization" first appeared around 1867, in Germany or Hungary. In English, Merriam-Webster dates the first known use of the verb "pasteurize" to 1881 and the noun "pasteurization" to 1886.

The method also moved beyond wine. According to the Science History Institute, Pasteur's process was used to preserve wine and beer until the mid-20th century, and by that point it had become common practice to pasteurize cow's milk as well. The Institut Pasteur adds that the method is no longer widely used for wine, because it can change the taste. That shift explains today's search data: "milk pasteurization" now sits at the top, even though the story began in a wine cellar.

Pasteurization vs sterilization

The two words are often swapped. They are not the same.

Notice the word Merriam-Webster chose: partial sterilization. Britannica and the International Dairy Foods Association both describe pasteurization as aimed at specific microorganisms. "Partial" is the tell: pasteurization goes part of the way, and sterilization is the word for going all the way.

You can see the difference in how the dairy trade group sorts its methods. It describes ultra-pasteurized products as lasting longer but still needing refrigeration. It reserves "commercially sterile" language for aseptic processing, where milk is heat-treated in sterile equipment and filled into hermetically sealed packaging, and the product is shelf stable until opened. Same family of heat processes, different end points.

The pasteurization process: the named methods

"Pasteurization process" is a top search, and the answer is that there is more than one. Here is how the International Dairy Foods Association describes the main methods for dairy, in general terms:

• Vat, or batch, pasteurization: the original method. Milk is heated in a large tank and held for a set time. The trade group says it is now used mainly for some cheese, yogurt, and buttermilk starter cultures and some ice cream mixes.
• High temperature short time (HTST): milk flows between metal plates warmed by hot water, is held briefly, and is then cooled quickly. The trade group calls it the most common method in the United States today.
• Higher heat shorter time (HHST): a variant of HTST that uses different equipment, higher heat, and even shorter times.
• Ultra-pasteurization: higher heat again, for a product that keeps longer but still needs refrigeration.
• Aseptic processing (UHT): heat treatment in commercially sterile equipment, followed by sealed packaging, for a shelf-stable product.

The US Department of Agriculture's National Agricultural Library thesaurus defines HTST as the time and temperature combination used for pasteurizing milk and milk products, and files it under the broader heading of pasteurization. In everyday dairy usage, "flash pasteurization" is the informal name for this HTST approach: a quick, high-heat pass rather than a long, slow hold. The pattern across every method is the same trade-off. More heat means less time.

Why "heat-treated" shows up on some probiotic labels

Here is where the heat process meets the supplement aisle. Some labels list a culture as "heat-treated." That phrase means what it says: the culture was deliberately exposed to heat during production, so the label is describing a processing step, the same broad idea Pasteur applied to wine.

Researchers have used several names for cultures that are no longer alive. A 2022 review in the journal Foods, written by members of the International Scientific Association for Probiotics and Prebiotics (ISAPP), lists older terms including "non-viable probiotics," "heat-killed probiotics," "tyndallized probiotics," and "paraprobiotics," and notes they were used inconsistently before ISAPP's 2021 consensus definition. The same review gives a food example of the idea: ambient yogurt that is heat-treated after fermentation to inactivate its starter cultures. The term that consensus settled on is postbiotic, which our guide to prebiotic, probiotic, and postbiotic meaning defines alongside the other two label words.

The takeaway for reading a label: "heat-treated" tells you how a culture was processed. It is a manufacturing description, and now you know the history behind it.

Our take on reading "pasteurized" and "heat-treated"

We like words with a clear origin. Pasteurization is one of the best: a named scientist, a dated patent, and a process you can describe in one sentence.

We think the most useful habit is to read process words as process words. "Pasteurized," "ultra-pasteurized," and "heat-treated" each tell you what happened during production. They describe a step, not a promise.

And when two words get swapped, like pasteurization and sterilization, go back to the dictionary. The difference is usually sitting in a single word, like "partial."

Why we carry it at PRSPR

The phrase "heat-treated" appears on the listing for our FLORÉ Probiotic, which is part of why we wrote this piece about the heat process and its history. Here is what the listing states about the product itself:

• What it is: a daily synbiotic with saffron.
• Format: 30 capsules, one capsule per serving, for 30 servings.
• On the label: its ingredient list includes Lactobacillus rhamnosus, listed as a heat-treated culture.
• Price: $61.36.

It is made in a GMP-certified facility and third-party batch tested. You can see it with related products in our Gut & Digestion collection.

See the FLORÉ Probiotic at PRSPR

FAQ

What is pasteurization?

Pasteurization is a controlled heat treatment named after Louis Pasteur. Merriam-Webster defines it as partial sterilization of a substance, especially a liquid such as milk, that destroys objectionable organisms without major chemical alteration of the substance.

Who invented pasteurization?

The process is named for the French scientist Louis Pasteur. The Institut Pasteur records that he filed a patent for a wine preservation process on 11 April 1865, while noting that heating wine was known before his work.

When was pasteurization invented?

The Science History Institute dates Pasteur's finding on heating wine to 1864, and the Institut Pasteur dates his patent to 1865. Britannica places the work in the 1860s.

What is flash pasteurization?

Flash pasteurization is the common name for the high temperature short time (HTST) approach: a brief, high-heat pass followed by quick cooling. The International Dairy Foods Association calls HTST the most common pasteurization method in the United States today.

Is pasteurization the same as sterilization?

No. Merriam-Webster calls pasteurization "partial" sterilization, and dairy industry definitions reserve "commercially sterile" for aseptic processing with sealed packaging.