Who discovered the pasteurization process

Pasteurization - Pasteurization

Process of preserving food with heat
Pasteurized milk in Japan
A Chicago Department of Health poster explains home pasteurization to mothers

pasteurization or pasteurization is a process in which packaged and unpackaged foods (such as milk and fruit juice) are treated with mild heat, usually below 100 ° C, to eliminate pathogens and extend shelf life. The method is designed to destroy or inactivate organisms and enzymes that contribute to spoilage or disease risk, including vegetative bacteria but not bacterial spores.

The process was named after the French microbiologist Louis Pasteur, whose research in the 1860s showed that thermal processing would deactivate unwanted microorganisms in wine. Corruption enzymes are also inactivated during pasteurization. Today pasteurization is widely used in the dairy and other food processing industries to achieve food preservation and food safety.

Until 1999, most liquid products were heat treated in a continuous system in which heat can be applied using a plate heat exchanger or the direct or indirect use of hot water and steam. Due to the mild heat, there are minor changes in the nutritional quality and sensory properties of the treated foods. Pascalization or high pressure processing (HPP) and pulsed electric field (PEF) are non-thermal processes that are also used to pasteurize food.


Louis Pasteur's pasteurization experiment shows that liquid spoilage was caused by particles in the air rather than the air itself. These experiments provided important evidence for the idea of ​​the germ theory of disease.

The process of heating wine for preservation purposes has been known in China since 1117 and was in the journal in Japan Tamonin-nikki documented, which was written between 1478 and 1618 by a number of monks.

Much later, in 1768, research by the Italian priest and scientist Lazzaro Spallanzani proved that a product can be made "sterile" after thermal processing. Spallanzani cooked meat broth for an hour, sealed the container immediately after boiling, noting that the broth did not spoil and was free of microorganisms. In 1795, a Parisian chef and pastry chef named Nicolas Appert began experimenting with ways to preserve food, followed by soups, vegetables, juices, dairy products, jellies, jams and syrups. He put the food in jars, sealed them with cork and sealing wax, and put them in boiling water. In the same year, the French military offered a cash prize of CHF 12,000 for a new method of food preservation. After 14 or 15 years of experimentation, Appert submitted his invention and won the award in January 1810. Later that year, Appert published L'art de conserver les substances animales et végétales (" The art of animal and vegetable substances too preserve "). This was the first cookbook of its kind on modern methods of food preservation.

La Maison Appert (English: The House of Appert) in the city of Massy near Paris was the first bottling factory in the world, in which various foods were kept in sealed bottles. Appert's method was to fill thick, mouth-sized glass bottles with products of all kinds, from beef and poultry to eggs, milk and prepared dishes. He left the headspace on top of the bottle and the cork was then tightly closed in the glass with a vice. The bottle was then wrapped in canvas to protect it while it was immersed in boiling water and then boiled for as long as Appert deemed it appropriate to thoroughly boil the contents. Appert patented his method that him honor sometimes as Appertization called has been.

Appert's method was so simple and practical that it spread quickly. The British inventor and merchant Peter Durand, also of French origin, patented his own method in 1810, but this time in a tin can, creating the modern process for canning food. In 1812, the Englishmen Bryan Donkin and John Hall both acquired patents and began making canned goods. Just a decade later, Appert's canning method had found its way to America. The manufacture of tin cans was not common until the beginning of the 20th century, partly because a hammer and chisel were required to open cans until Robert Yeates invented a can opener in 1855.

A less aggressive method was developed by the French chemist Louis Pasteur during a summer vacation in Arbois in 1864. In order to remedy the common acidity of locally matured wines, he found experimentally that it is sufficient to heat a young wine to only around 50–60 ° C for a short time to kill the microbes, and that too. The wine could then be matured without affecting the final quality. In honor of Pasteur, this process is known as "pasteurization". Pasteurization was originally used to prevent wine and beer from going sour, and it would take many years to pasteurize the milk. In the United States by the 1870s, it was common practice for milk to contain substances designed to mask spoilage before milk was regulated.


180 kg of milk in a cheese vat

Milk is an excellent medium for microbial growth, and if stored at ambient temperature, bacteria and other pathogens will soon multiply. According to the U.S. Centers for Disease Control (CDC), raw milk, if improperly handled, is responsible for nearly three times more hospital stays than any other food-borne disease source. This makes it one of the most dangerous food products in the world. Diseases prevented by pasteurization can include tuberculosis, brucellosis, diphtheria, scarlet fever, and Q fever. it also kills the harmful bacteria, among other things Salmonella , Listeria , Yersinia , Campylobacter , Staphylococcus aureus and Escherichia coli O157: H7 from .

Before industrialization, dairy cows were kept in urban areas to limit the time between milk production and consumption. Therefore, the risk of disease transmission via raw milk has been reduced. As urban density increased and supply chains stretched to the distance from country to town, raw milk (often days old) was recognized as a source of disease. For example, between 1912 and 1937, 65,000 people died of tuberculosis caused by milk consumption in England and Wales alone. Because tuberculosis has a long incubation period in humans, it has been difficult to link unpasteurized milk consumption to the disease. In 1892, chemist Ernst Lederle experimentally inoculated milk from cows with tuberculosis disease in guinea pigs, which is how they developed the disease. In 1910 Lederle, then as health commissioner, introduced the mandatory pasteurization of milk in New York City.

Developed countries have introduced pasteurization of milk to prevent such diseases and deaths. As a result, milk is now considered a safer food. A traditional form of pasteurization by scalding and sifting cream to improve the shelf life of butter was practiced in Britain in the 18th century and introduced in Boston in the British colonies in 1773, although it was not widely used in the United States for the next 20 years. The pasteurization of milk was proposed by Franz von Soxhlet in 1886. At the beginning of the 20th century, Milton Joseph Rosenau set the standards for pasteurizing milk - that is, slowly heating it to 60 ° C (140 ° F) for 20 minutes during his time with the United States Marine Hospital Service, especially his release of The Milk Question (1912). The US states soon began enacting mandatory pasteurization laws for dairy products, the first in 1947, and in 1973 the US federal government required the pasteurization of milk, which is used in every international trade.

The shelf life of chilled pasteurized milk is longer than that of raw milk. For example, high-temperature pasteurized milk (HTST) typically has a refrigerated shelf life of two to three weeks, whereas ultra-pasteurized milk can keep much longer, sometimes two to three months. When ultra heat treatment (UHT) is combined with sterile handling and container technology (e.g. aseptic packaging), it can even be stored unrefrigerated for up to 9 months.

According to the Centers for Disease Control, between 1998 and 2011, 79% of dairy disease outbreaks in the US were due to raw milk or cheese products. They report 148 outbreaks and 2,384 diseases (284 must be hospitalized), as well as two deaths from raw milk or cheese products in the same period.

Medical equipment

Medical devices, particularly breathing and anesthetic devices, are often disinfected with hot water as an alternative to chemical disinfection. The temperature is increased to 70 ° C (158 ° F) for 30 minutes.

Pasteurization process

General overview of the pasteurization process. The milk begins on the left and enters the pipelines with functioning enzymes, which are denatured during heat treatment and impair the function of the enzymes. This helps stop pathogen growth by stopping the cell from functioning. The cooling process prevents the milk from going through the Maillard reaction and caramelization. The pasteurization process also has the ability to heat the cells to the point where pressure build-up causes them to burst.

Pasteurization is a mild heat treatment of liquid food (both packaged and unpackaged) in which products are typically heated to below 100 ° C. The heat treatment and cooling process should prevent a phase change of the product. The acidity of the food determines the parameters (time and temperature) of the heat treatment, as well as the shelf life. The parameters also take into account nutritionally sensitive nutritional and sensory properties.

In acidic foods (pH <4.6) such as fruit juice and beer, the heat treatments are intended to inactivate enzymes (pectin methylesterase and polygalacturonase in fruit juices) and destroy spoiling microbes (yeast and lactobacillus). Because of the low pH of acidic foods, pathogens cannot grow. This extends the shelf life by several weeks. In less acidic foods (pH> 4.6) such as milk and liquid eggs, the heat treatments are intended to destroy pathogens and spoilage organisms (yeast and mold). Not all spoilage organisms are destroyed under pasteurization parameters, so subsequent cooling is necessary.


Food can be pasteurized in two ways: either before or after packing in containers. When food is packaged in glass, hot water is used to reduce the risk of thermal shock. Plastics and metals are also used in food packaging and these are generally pasteurized with steam or hot water as the risk of thermal shock is low.

Most liquid foods are pasteurized using continuous systems that have a heating zone, a holding tube and a cooling zone, after which the product is filled into the package. Plate heat exchangers are used for low viscosity products such as animal milk, nut milk and juices. A plate heat exchanger consists of many thin vertical stainless steel plates that separate the liquid from the heating or cooling medium. Scraped surface heat exchangers contain an internal rotating shaft in the tube and are used to scrape off highly viscous material that may collect on the wall of the tube.

Shell or tube heat exchangers designed for pasteurizing food are non-Newtonian liquids, such as dairy products, tomato ketchup and baby food. A tube heat exchanger consists of concentric stainless steel tubes. Food passes through the inner tube while the heating / cooling medium circulates through the outer or inner tube.

Using a heat exchanger to pasteurize unpackaged food over pasteurizing food in containers offers the following advantages:

  • Heat exchangers ensure uniform treatment and there is greater flexibility in the products that can be pasteurized on these plates
  • The process is more energy efficient than pasteurizing food in packaged containers
  • Higher throughput

After being heated in a heat exchanger, the product flows through a holding tube for a specified period of time in order to achieve the required treatment. If the pasteurization temperature or time is not reached, a flow diverter valve is used to divert the underprocessed product back to the raw product tank. When the product is sufficiently processed, it is cooled in a heat exchanger and then filled.

High-temperature short-term pasteurization (HTST), such as that used for milk (71.5 ° C (160.7 ° F) for 15 seconds), ensures the safety of the milk and offers a refrigerated shelf life of approximately two weeks. With ultra-high temperature pasteurization (UHT), milk is pasteurized for 1–2 seconds at 135 ° C, which offers the same level of safety but, together with the packaging, extends the shelf life to three months.


Direct microbiological techniques are the ultimate measure of contamination with pathogens. However, these are costly and time consuming. This means that products will have a shorter shelf life until pasteurization is checked.

Because of the inappropriateness of microbiological techniques, the effectiveness of milk pasteurization is typically monitored by checking for the presence of alkaline phosphatase, which is denatured by pasteurization. The destruction of the alkaline phosphatase ensures the destruction of common milk pathogens. Therefore, the presence of alkaline phosphatase is an ideal indicator of the effectiveness of pasteurization. In the case of liquid eggs, the effectiveness of the heat treatment is measured using the residual activity of the α-amylase.

Effectiveness against pathogenic bacteria

During the early 20th century, there was no solid understanding of what time and temperature combinations would inactivate pathogenic bacteria in milk, and therefore a number of different pasteurization standards were used. By 1943, both HTST pasteurization conditions of 72 ° C (162 ° F) for 15 seconds and batch pasteurization conditions of 63 ° C (145 ° F) for 30 minutes were best confirmed by total thermal death (as) studies, such as could be measured at this point) for a number of pathogenic bacteria in milk. Later a complete inactivation of Coxiella burnetii (which was then believed to cause Q fever from oral ingestion of infected milk) and by Mycobacterium tuberculosis (which causes tuberculosis) detected. For all practical purposes, these conditions were sufficient to destroy almost all yeasts, molds and common spoilage bacteria and to ensure adequate destruction of common pathogenic refractory organisms. However, the microbiological techniques used until the 1960s did not make it possible to enumerate the actual reduction in bacteria. Evidence of the extent to which pathogenic bacteria are inactivated by milk pasteurization came from a study of surviving bacteria in milk that was heat-treated after being deliberately exposed to high concentrations of the most heat-resistant strains of the major milk-borne pathogens.

The middle log 10- Reductions and inactivation temperatures of the most important milk-borne pathogens during a 15-second treatment are:

  • Staphylococcus aureus > 6.7 at 66.5 ° C (151.7 ° F)
  • Yersinia enterocolitica > 6.8 at 62.5 ° C (144.5 ° F)
  • pathogenic Escherichia coli > 6.8 at 65 ° C (149 ° F)
  • Cronobacter sakazakii > 6.7 at 67.5 ° C (153.5 ° F)
  • Listeria monocytogenes > 6.9 at 65.5 ° C (149.9 ° F)
  • Salmonella ser. Typhimurium> 6.9 at 61.5 ° C (142.7 ° F)

(A log 10- A reduction between 6 and 7 means that 1 bacterium in 1 million (10th 6 ) to 10 million (10 7 ) Bacteria survived the treatment.)

The Codex Alimentarius Code of Hygienic Practice for Milk notes that the pasteurization of milk is designed so that Coxiella burnetii by at least 5 log 10 is reduced. The Code also states that: "The minimum pasteurization conditions are those with bactericidal effects equivalent to heating each milk particle to 72 ° C for 15 seconds (continuous flow pasteurization) or 63 ° C for 30 minutes (batch pasteurization). " "To ensure that each particle is sufficiently heated, the milk flow in heat exchangers should be turbulent, d . H. The Reynolds number should be sufficiently high. "The point about turbulent flow is important because simplified laboratory heat inactivation studies using non-flow test tubes show less bacterial inactivation than larger-scale experiments attempting to replicate commercial pasteurization conditions.

As a precautionary measure, modern HTST pasteurization processes must be designed with flow restrictions and bypass valves to ensure that the milk is heated evenly and that no part of the milk is exposed to a shorter time or lower temperature. It is common for temperatures to exceed 72 ° C by 1.5 ° C or 2 ° C.

Double pasteurization

Since pasteurization is not sterilization and does not kill spores, a second "double" pasteurization extends the shelf life by killing germinated spores.

Acceptance of double pasteurization varies by jurisdiction. In places where this is allowed, initial pasteurization is usually done when the milk has been collected at the farm so that it does not spoil before processing. In many countries it is not allowed to simply label such milk as "grazing". Therefore, thermization, a process at lower temperatures, is used instead.

Effects on the nutritional and sensory properties of food

Due to the mild heat treatment, pasteurization increases the shelf life by a few days or weeks. However, this mild heat also means that the heat-labile vitamins in the food are only slightly changed.


According to a systematic review and meta-analysis, it was found that pasteurization appeared to decrease levels of vitamins B12 and E, but also increased levels of vitamins A. Apart from the meta-analysis, it is not possible to draw conclusions about the effect of pasteurization on vitamins A, B12 and E based solely on a consultation of the extensive literature available. Milk is not a major source of vitamins B12 or E in the North American diet, so the effects of pasteurization on the daily intake of these vitamins by adults are negligible. However, milk is considered an important source of vitamin A. Since pasteurization appears to increase the concentration of vitamin A in milk, the effect of milk heat treatment on this vitamin is not a major public health concern. Meta-analysis results show that pasteurization of milk leads to a significant decrease in vitamin C and folic acid, but milk is not an important source of these vitamins either. A significant decrease in vitamin B2 concentrations was found after pasteurization. Vitamin B2 is typically found in bovine milk in concentrations of 1.83 mg / liter. Since the recommended daily allowance for adults is 1.1 mg / day, milk consumption contributes significantly to the recommended daily allowance of this vitamin. With the exception of B2, pasteurization does not appear to be a problem in reducing the nutritional value of milk, as milk is often not a major source of these studied vitamins in the North American diet.

Sensory effects

Pasteurization also has a small but measurable impact on the sensory properties of the processed foods. Pasteurization in fruit juices can lead to the loss of volatile flavoring substances. Fruit juice products undergo a venting process prior to pasteurization, which can be responsible for this loss. The vent also minimizes the loss of nutrients like vitamin C and carotene. To prevent degradation due to the loss of volatile compounds, volatile recovery, while costly, can be used to produce higher quality juice products.

In terms of color, the pasteurization process does not have much of an impact on pigments such as chlorophylls, anthocyanins and carotenoids in plant and animal tissues. In fruit juices, polyphenol oxidase (PPO) is the main enzyme responsible for browning and color changes. However, this enzyme is deactivated in the deaeration step prior to pasteurization with removal of oxygen.

In milk, the color difference between pasteurized and raw milk is related to the homogenization step that takes place before pasteurization. Before pasteurization, milk is homogenized in order to emulsify its fat- and water-soluble components, which means that the pasteurized milk has a whiter appearance compared to raw milk. In vegetable products, the degradation of color depends on the temperature conditions and the duration of heating.

Pasteurization can lead to some loss of texture due to enzymatic and non-enzymatic transformations in the structure of pectin if the processing temperatures are too high as a result. However, with mild pasteurization by heat treatment, softening of the tissues in the vegetables, which causes a loss of texture, is not a concern as long as the temperature does not rise above 80 ° C (176 ° F).

Novel pasteurization methods

Other thermal and nonthermal methods have been developed to pasteurize food to reduce the effects on the nutritional and sensory properties of food and to prevent the breakdown of heat-labile nutrients. Pascalization or High Pressure Processing (HPP) and Pulsed Electric Field (PEF) are examples of these non-thermal pasteurization processes that are currently in commercial use.

Microwave volumetric heating (MVH) is the latest pasteurization technology available. It uses microwaves to heat liquids, suspensions or semi-solids in a continuous flow. Since MVH releases energy evenly and deeply into the entire body of a flowing product, it enables gentler and shorter heating, so that almost all heat-sensitive substances are retained in the milk.

Low temperature, short time (LTST) is a patented process in which droplets are sprayed into a chamber that is heated below the usual pasteurization temperatures. The treatment of liquid products takes several thousandths of a second. This is why the process is also known as millisecond technology (MST). In combination with HTST, it significantly extends the shelf life of products (over 50 days) without affecting the nutrients or taste. LTST has been commercial since 2019.

Products that are usually pasteurized

See also


further reading

  • Raw Milk Expert Testimony, dated: April 25, 2008 Case: Organic Dairy Company, LLC and Claravale Farm, Inc., Plaintiff, v. No. CU-07-00204, State of California, and AG Kawamura, Secretary of the California Department of Food and Agriculture Agriculture , - Expert: Dr. Theodore Beals & Dr. Ronald Hull
  • An alternate view of the alleged safety of pasteurized milk versus natural milk from Johns Hopkins University: Realmilk.com, Webmaster (August 12, 2015). "The Johns Hopkins Raw Milk Study - A Campaign for Real Milk". A campaign for real milk .

External links