Pasteurization

Pasteurization

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Pasteurization is a process of heating a food, usually liquid, to a specific temperature for a definite length of time, and then cooling it immediately. This process slows microbial growth in food
Food
Food is any substance consumed to provide nutritional support for the body. It is usually of plant or animal origin, and contains essential nutrients, such as carbohydrates, fats, proteins, vitamins, or minerals...

. The process of heating wine for preservation purposes has been known in China since 1117, and is documented in Japan in 1568 in the diary Tamonin-nikki, but the modern version involving immediate cooling was created by the French
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...

 chemist and microbiologist Louis Pasteur
Louis Pasteur
Louis Pasteur was a French chemist and microbiologist born in Dole. He is remembered for his remarkable breakthroughs in the causes and preventions of diseases. His discoveries reduced mortality from puerperal fever, and he created the first vaccine for rabies and anthrax. His experiments...

, after whom it is named. The first pasteurization test was completed by Louis Pasteur and Claude Bernard
Claude Bernard
Claude Bernard was a French physiologist. He was the first to define the term milieu intérieur . Historian of science I. Bernard Cohen of Harvard University called Bernard "one of the greatest of all men of science"...

 in April 1862. The process was originally conceived as a way of preventing wine
Wine
Wine is an alcoholic beverage, made of fermented fruit juice, usually from grapes. The natural chemical balance of grapes lets them ferment without the addition of sugars, acids, enzymes, or other nutrients. Grape wine is produced by fermenting crushed grapes using various types of yeast. Yeast...

 and beer
Beer
Beer is the world's most widely consumed andprobably oldest alcoholic beverage; it is the third most popular drink overall, after water and tea. It is produced by the brewing and fermentation of sugars, mainly derived from malted cereal grains, most commonly malted barley and malted wheat...

 from souring.

Unlike sterilization
Sterilization (microbiology)
Sterilization is a term referring to any process that eliminates or kills all forms of microbial life, including transmissible agents present on a surface, contained in a fluid, in medication, or in a compound such as biological culture media...

, pasteurization is not intended to kill all micro-organisms in the food. Instead pasteurization aims to reduce the number of viable pathogens so they are unlikely to cause disease (assuming the pasteurized product is stored as indicated and consumed before its expiration date). Commercial-scale sterilization of food is not common because it adversely affects the taste and quality of the product. Certain food products, like dairy products, are superheated to ensure pathogenic microbes are destroyed.

Pasteurization of milk


Pasteurization is typically associated with milk
Milk
Milk is a white liquid produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals before they are able to digest other types of food. Early-lactation milk contains colostrum, which carries the mother's antibodies to the baby and can reduce the risk of many...

. Pasteurization [i.e., scalding and straining] of cream to increase the keeping qualities of butter was practiced in England before 1773 and had been introduced to Boston, New England, by 1773, although it was not widely practiced in the US for the next twenty years. It was still being written of as a new process in American newspapers as late as 1802.

Pasteurization of milk was suggested by Franz von Soxhlet
Franz von Soxhlet
Franz Ritter von Soxhlet was a German agricultural chemist from Brno. He invented the Soxhlet extractor in 1879 and in 1886 he proposed that pasteurization be applied to milk and other.-References:...

 in 1886. It is the main reason for milk's extended shelf life. High Temperature Short Time (HTST) pasteurized milk typically has a refrigerated
Refrigeration
Refrigeration is a process in which work is done to move heat from one location to another. This work is traditionally done by mechanical work, but can also be done by magnetism, laser or other means...

 shelf life
Shelf life
Shelf life is the length of time that food, drink, medicine, chemicals, and many other perishable items are given before they are considered unsuitable for sale, use, or consumption...

 of two to three weeks, whereas ultra-pasteurized milk can last much longer, sometimes two to three months. When ultra-heat treatment (UHT) is combined with sterile handling and container technology (such as aseptic packaging
Aseptic processing
Aseptic processing is the process by which a sterile product is packaged in a sterile container in a way that maintains sterility...

), it can even be stored unrefrigerated for 6–9 months

Pasteurization typically uses temperatures below boiling since at very high temperatures casein
Casein
Casein is the name for a family of related phosphoprotein proteins . These proteins are commonly found in mammalian milk, making up 80% of the proteins in cow milk and between 60% and 65% of the proteins in human milk....

 micelle
Micelle
A micelle is an aggregate of surfactant molecules dispersed in a liquid colloid. A typical micelle in aqueous solution forms an aggregate with the hydrophilic "head" regions in contact with surrounding solvent, sequestering the hydrophobic single tail regions in the micelle centre. This phase is...

s will irreversibly aggregate, or "curdle." There are two main types of pasteurization used today: High Temperature/Short Time (HTST)
Flash pasteurization
Flash pasteurization, also called "High Temperature Short Time" processing, is a method of heat pasteurization of perishable beverages like fruit and vegetable juices, beer, and some dairy products...

 and "Extended Shelf Life (ESL)" treatment. Ultra-high temperature (UHT or ultra-heat treated) is also used for milk treatment. In the HTST process, milk is forced between metal plates or through pipes heated on the outside by hot water, and is heated to 71.7 °C (161 °F) for 15–20 seconds. UHT processing holds the milk at a temperature of 135 °C (275 °F) for a minimum of one second. ESL milk has a microbial-filtration step and lower temperatures than UHT milk. Milk simply labeled "pasteurized" is usually treated with the HTST method, whereas milk labeled "ultra-pasteurized" or simply "UHT" has been treated with the UHT method. Since 2007, however, it is no longer a legal requirement in European countries (such as Germany) to declare ESL milk as ultra-heated, consequently, it is now often labeled as "fresh milk" and just advertised as having an "extended shelf life", making it increasingly difficult to distinguish ESL milk from traditionally pasteurized fresh milk. A less conventional but US FDA-legal alternative (typically for home pasteurization) is to heat milk at 145 °F (62.8 °C) for 30 minutes.

Proponents of unpasteurized milk make the unfounded and incorrect argument that if milk is obtained from humanely raised cows that are grass fed and handled hygienically, then there is little problem with disease. However, raw milk can become contaminated in a number of ways: by coming into contact with cow feces or bacteria living on the skin of cows, from an infection of the cow's udder, or from dirty equipment, among others. Raw milk is responsible for nearly three times more hospitalizations than any other foodborne disease outbreak, making it one of the world's most dangerous food products.

Pasteurization methods are usually standardized and controlled by national food safety agencies (such as the USDA
United States Department of Agriculture
The United States Department of Agriculture is the United States federal executive department responsible for developing and executing U.S. federal government policy on farming, agriculture, and food...

 in the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 and the Food Standards Agency
Food Standards Agency
The Food Standards Agency is a non-ministerial government department of the Government of the United Kingdom. It is responsible for protecting public health in relation to food throughout the United Kingdom and is led by a board appointed to act in the public interest...

 in the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

). These agencies require milk to be HTST pasteurized in order to qualify for the "pasteurization" label. There are different standards for different dairy products, depending on the fat content and the intended usage. For example, the pasteurization standards for cream
Cream
Cream is a dairy product that is composed of the higher-butterfat layer skimmed from the top of milk before homogenization. In un-homogenized milk, over time, the lighter fat rises to the top. In the industrial production of cream this process is accelerated by using centrifuges called "separators"...

 differ from the standards for fluid milk, and the standards for pasteurizing cheese
Cheese
Cheese is a generic term for a diverse group of milk-based food products. Cheese is produced throughout the world in wide-ranging flavors, textures, and forms....

 are designed to preserve the phosphatase
Phosphatase
A phosphatase is an enzyme that removes a phosphate group from its substrate by hydrolysing phosphoric acid monoesters into a phosphate ion and a molecule with a free hydroxyl group . This action is directly opposite to that of phosphorylases and kinases, which attach phosphate groups to their...

 enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

, which aids in cutting.

In Canada, all milk produced at a processor and intended for consumption must be pasteurized, legally requiring it to be heated to at least 72 degrees Celsius for at least 16 seconds and then cooling it to 4 degrees Celsius. This ensures that any harmful bacteria are destroyed.

The HTST pasteurization standard was designed to achieve a 5-log reduction, killing 99.999% of the number of viable micro-organisms in milk. This is considered adequate for destroying almost all yeast
Yeast
Yeasts are eukaryotic micro-organisms classified in the kingdom Fungi, with 1,500 species currently described estimated to be only 1% of all fungal species. Most reproduce asexually by mitosis, and many do so by an asymmetric division process called budding...

s, mold
Mold
Molds are fungi that grow in the form of multicellular filaments called hyphae. Molds are not considered to be microbes but microscopic fungi that grow as single cells called yeasts...

s, and common spoilage bacteria and also to ensure adequate destruction of common pathogenic heat-resistant organisms (including Mycobacterium tuberculosis
Mycobacterium tuberculosis
Mycobacterium tuberculosis is a pathogenic bacterial species in the genus Mycobacterium and the causative agent of most cases of tuberculosis . First discovered in 1882 by Robert Koch, M...

,
which causes tuberculosis
Tuberculosis
Tuberculosis, MTB, or TB is a common, and in many cases lethal, infectious disease caused by various strains of mycobacteria, usually Mycobacterium tuberculosis. Tuberculosis usually attacks the lungs but can also affect other parts of the body...

, but not Coxiella burnetii
Coxiella burnetii
Coxiella burnetii is an obligate intracellular bacterial pathogen, and is the causative agent of Q fever. The genus Coxiella is morphologically similar to Rickettsia, but with a variety of genetic and physiological differences. C...

,
which causes Q fever
Q fever
Q fever is a disease caused by infection with Coxiella burnetii, a bacterium that affects humans and other animals. This organism is uncommon but may be found in cattle, sheep, goats and other domestic mammals, including cats and dogs...

). HTST pasteurization processes must be designed so that the milk is heated evenly, and no part of the milk is subject to a shorter time or a lower temperature.

A process similar to pasteurization is thermization
Thermization
Thermization, also spelled thermisation, is a method of sterilizing raw milk with heat. The process is not used on other food products, and is similar to pasteurization but uses lower temperatures, allowing the milk product to retain more of its original taste. In Europe, there is a distinction...

, which uses lower temperatures to kill bacteria in milk. It allows a milk product, such as cheese, to retain more of the original taste, but thermized foods are not considered pasteurized by food regulators.

Effectiveness of pasteurization


Milk pasteurization has been scientifically proven to be at least 90% effective in eliminating harmful bacteria in milk. While there are some few pathogens which are heat resistant,modern equipment is readily able to test and identify bacteria in milk being processed. Pasteurization is the only effective means of eliminating 90% or more of harmful organisms in milk.

Non pasteurized, raw, milk, according to the Centers for Disease Control (CDC), was responsible for 86 reported food poisoning outbreaks between 1998 and 2008, resulting in 1,676 illnesses, 191 hospitalizations, and two deaths. Raw milk is responsible for nearly three times more hospitalizations than any other foodborne disease outbreak.

Diseases that pasteurization can prevent include tuberculosis
Tuberculosis
Tuberculosis, MTB, or TB is a common, and in many cases lethal, infectious disease caused by various strains of mycobacteria, usually Mycobacterium tuberculosis. Tuberculosis usually attacks the lungs but can also affect other parts of the body...

, brucellosis
Brucellosis
Brucellosis, also called Bang's disease, Crimean fever, Gibraltar fever, Malta fever, Maltese fever, Mediterranean fever, rock fever, or undulant fever, is a highly contagious zoonosis caused by ingestion of unsterilized milk or meat from infected animals or close contact with their secretions...

, diphtheria
Diphtheria
Diphtheria is an upper respiratory tract illness caused by Corynebacterium diphtheriae, a facultative anaerobic, Gram-positive bacterium. It is characterized by sore throat, low fever, and an adherent membrane on the tonsils, pharynx, and/or nasal cavity...

, scarlet fever
Scarlet fever
Scarlet fever is a disease caused by exotoxin released by Streptococcus pyogenes. Once a major cause of death, it is now effectively treated with antibiotics...

, and Q-fever; it also kills the harmful bacteria Salmonella
Salmonella
Salmonella is a genus of rod-shaped, Gram-negative, non-spore-forming, predominantly motile enterobacteria with diameters around 0.7 to 1.5 µm, lengths from 2 to 5 µm, and flagella which grade in all directions . They are chemoorganotrophs, obtaining their energy from oxidation and reduction...

, Listeria, Yersinia
Yersinia
Yersinia is a genus of bacteria in the family Enterobacteriaceae. Yersinia are Gram-negative rod shaped bacteria, a few micrometers long and fractions of a micrometer in diameter, and are facultative anaerobes. Some members of Yersinia are pathogenic in humans; in particular, Y. pestis is the...

, Campylobacter
Campylobacter
Campylobacter is a genus of bacteria that are Gram-negative, spiral, and microaerophilic. Motile, with either unipolar or bipolar flagella, the organisms have a characteristic spiral/corkscrew appearance and are oxidase-positive. Campylobacter jejuni is now recognized as one of the main causes...

, Staphylococcus aureus
Staphylococcus aureus
Staphylococcus aureus is a facultative anaerobic Gram-positive coccal bacterium. It is frequently found as part of the normal skin flora on the skin and nasal passages. It is estimated that 20% of the human population are long-term carriers of S. aureus. S. aureus is the most common species of...

, and Escherichia coli
Escherichia coli
Escherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...

 157 among others.

Side-effects of pasteurization


Fans of raw milk
Raw milk
Raw milk is milk that has not been pasteurized or homogenized.-History:Humans consumed raw milk exclusively prior to the industrial revolution and the invention of the pasteurization process in 1864. During the industrial revolution large populations congregated into urban areas detached from the...

 (meaning milk
Milk
Milk is a white liquid produced by the mammary glands of mammals. It is the primary source of nutrition for young mammals before they are able to digest other types of food. Early-lactation milk contains colostrum, which carries the mother's antibodies to the baby and can reduce the risk of many...

 that hasn't been pasteurized or homogenized) credit it with having more beneficial bacteria
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

 and enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

s than its processed counterpart. However, raw milk cannot be preserved
Preservation
Preservation may refer to:* Heritage preservation:** Historic preservation, of buildings, monuments, etc.** Preservation , of books, recordings, etc.** Conservation , of the natural environment...

 for a long time and its disadvantages may exceed its benefits. In fact, raw milk is far more likely to contain harmful microbial contaminants, and pasteurization is the only effective way of killing most of pathogen
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...

 bacteria — which can include a.o., listeria, salmonella
Salmonella
Salmonella is a genus of rod-shaped, Gram-negative, non-spore-forming, predominantly motile enterobacteria with diameters around 0.7 to 1.5 µm, lengths from 2 to 5 µm, and flagella which grade in all directions . They are chemoorganotrophs, obtaining their energy from oxidation and reduction...

, and E. coli.. On the other hand raw milk does contain antimicrobial properties which are destroyed with the heat of pasturization, along with many of the vitamins within the milk itself . Raw milk has also been shown to influence the immune system with a protective effect of raw milk consumption on the development of asthma
Asthma
Asthma is the common chronic inflammatory disease of the airways characterized by variable and recurring symptoms, reversible airflow obstruction, and bronchospasm. Symptoms include wheezing, coughing, chest tightness, and shortness of breath...

, hay fever
Hay Fever
Hay Fever is a comic play written by Noël Coward in 1924 and first produced in 1925 with Marie Tempest as the first Judith Bliss. Laura Hope Crews played the role in New York...

, and atopic sensitization
Atopy
Atopy or atopic syndrome is a predisposition toward developing certain allergic hypersensitivity reactions.Atopy may have a hereditary component, although contact with the allergen must occur before the hypersensitivity reaction can develop ....

, although the mechanism is not entirely understood

Products that are commonly pasteurized

  • Canned food
  • Dairy products
  • Juice
    Juice
    Juice is the liquid that is naturally contained in fruit or vegetable tissue.Juice is prepared by mechanically squeezing or macerating fruit or vegetable flesh without the application of heat or solvents. For example, orange juice is the liquid extract of the fruit of the orange tree...

    s
  • Low alcoholic beverages
  • Syrups
  • Vinegar
    Vinegar
    Vinegar is a liquid substance consisting mainly of acetic acid and water, the acetic acid being produced through the fermentation of ethanol by acetic acid bacteria. Commercial vinegar is produced either by fast or slow fermentation processes. Slow methods generally are used with traditional...

  • Water
    Water
    Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

  • Wines

See also

  • Cold pasteurization
  • Flash pasteurization
    Flash pasteurization
    Flash pasteurization, also called "High Temperature Short Time" processing, is a method of heat pasteurization of perishable beverages like fruit and vegetable juices, beer, and some dairy products...

  • Pascalization
    Pascalization
    Pascalization, bridgmanization, or high pressure processing , is a method of preserving and sterilizing food, in which a product is processed under very high pressure, leading to the inactivation of certain microorganisms and enzymes in the food...

  • Homogenization
    Homogenization (chemistry)
    Homogenization or homogenisation is any of several processes used to make a chemical mixture the same throughout.-Definition:Homogenization is intensive blending of mutually related substances or groups of mutually related substances to form a constant of different insoluble phases to obtain a...

  • Pasteurized eggs
    Pasteurized eggs
    Pasteurized eggs are eggs that have been pasteurized in order to reduce the possibility of food-borne illness in dishes that are not cooked or lightly cooked...

  • Solar water disinfection
    Solar water disinfection
    Solar water disinfection, also known as SODIS is a method of disinfecting water using only sunlight and plastic PET bottles. SODIS is a free and effective method for decentralized water treatment, usually applied at the household level and is recommended by the World Health Organization as a viable...

  • Thermoduric bacteria
    Thermoduric bacteria
    Thermoduric bacteria are bacteria which can survive, to varying extents, the pasteurisation process. Species of bacteria which are thermoduric include Bacillus, Clostridium and Enterococci....

  • Food preservation
    Food preservation
    Food preservation is the process of treating and handling food to stop or slow down spoilage and thus allow for longer storage....

  • Food storage
    Food storage
    Food storage is both a traditional domestic skill and is important industrially. Food is stored by almost every human society and by many animals...

  • Food microbiology
    Food microbiology
    Food microbiology is the study of the microorganisms that inhabit, create, or contaminate food. Of major importance is the study of microorganisms causing food spoilage. "Good" bacteria, however, such as probiotics, are becoming increasingly important in food science...

  • Sterilization
    Sterilization (microbiology)
    Sterilization is a term referring to any process that eliminates or kills all forms of microbial life, including transmissible agents present on a surface, contained in a fluid, in medication, or in a compound such as biological culture media...

  • Thermization
    Thermization
    Thermization, also spelled thermisation, is a method of sterilizing raw milk with heat. The process is not used on other food products, and is similar to pasteurization but uses lower temperatures, allowing the milk product to retain more of its original taste. In Europe, there is a distinction...


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