Why does milk need to be pasteurized?

Proponents of raw milk (in the U.S.) advance two basic arguments for unpasteurized milk. They state that pasteurization destroys or damages some of the milk's nutrients, and that while pasteurization may kill dangerous bacteria, it also kills off good bacteria that raw milk supporters have stated to have health benefits. The United States Food and Drug administration has stated that this is false, and that pasteurizing milk does not destroy any of its nutritive value.

Raw milk

Raw milk or unpasteurized milk is milk that has not been pasteurized, a process of heating liquid foods to decontaminate them for safe drinking. Proponents of raw milk have stated that there are benefits to its consumption, including better flavor, better nutrition, and the building of a healthy immune system. However, the medical community has warned of the dangers, which include a risk of infection, and has not found any clear benefit. The availability and regulation of raw milk vary around the world. In the US, some dairies have adopted low-temperature vat pasteurization, which they say produces a product similar to raw milk.

Humans first learned to regularly consume the milk of other mammals following the domestication of animals during the Neolithic Revolution or the development of agriculture. This development occurred independently in several places around the world from as early as 9000–7000 BC in Mesopotamia to 3500–3000 BC in the Americas. The most important dairy animals—cattle, sheep and goats—were first domesticated in Mesopotamia, although domestic cattle had been independently derived from wild aurochs populations several times since. From there dairy animals spread to Europe (beginning around 7000 BC but not reaching Britain and Scandinavia until after 4000 BC), and South Asia (7000–5500 BC).

Pasteurization is widely used to prevent infected milk from entering the food supply. The pasteurization process was developed in 1864 by French scientist Louis Pasteur, who discovered that heating beer and wine was enough to kill most of the bacteria that caused spoilage, preventing these beverages from turning sour. The process achieves this by eliminating pathogenic microbes and lowering microbial numbers to prolong the quality of the beverage.

After sufficient scientific study led to the development of germ theory, pasteurization was introduced in the United States in the 1890s. This move successfully controlled the spread of highly contagious bacterial diseases including "E. coli", bovine tuberculosis and brucellosis (all thought to be easily transmitted to humans through the drinking of raw milk). In the early days after the scientific discovery of bacteria, there was no product testing to determine whether a farmer's milk was safe or infected, so all milk was treated as potentially contagious. After the first tests were developed, some farmers took steps to prevent their infected animals from being killed and removed from food production, sometimes even falsifying test results to make their animals appear free of infection. Recent advances in the analysis of milk-borne diseases have enabled scientists to track the DNA of the infectious bacteria to the cows on the farms that supplied the raw milk.

The recognition of many potentially deadly pathogens, such as "E. coli" 0157 H7, "Campylobacter", "Listeria", and "Salmonella", and their possible presence in poorly produced milk products has led to the continuation of pasteurization. The Department of Health and Human Services, Center for Disease Control and Prevention, and other health agencies of the United States strongly recommend that the public do not consume raw milk or raw milk products. Young children, the elderly, people with weakened immune systems, and pregnant women are more susceptible to infections originating in raw milk.

Milk can be repasteurized, as is done when pasteurized milk is shipped from the US mainland to Hawaii, which can be done to extend the expiration date.

Those favoring the consumption of raw milk believe that raw milk and associated products are more nutritious, build a healthy immune system and taste better. Those favoring the consumption of pasteurized milk consider the pathogen risk associated with drinking raw milk unacceptable.

Agencies such as the Centers for Disease Control and Prevention (CDC), and the Food and Drug Administration (FDA) in the United States, and other regulatory agencies around the world say that potential pathogens from raw milk, including possibly tuberculosis, diphtheria, typhoid, and streptococcal infections, make it potentially unsafe to consume. Similarly, a recent review authored by the Belgian Federal Agency for the Safety of the Food Chain and experts from Belgian universities and institutions concluded that "raw milk poses a realistic health threat due to a possible contamination with human pathogens. It is therefore strongly recommended that milk should be heated before consumption. With the exception of an altered organoleptic [flavor] profile, heating (particularly ultra high temperature and similar treatments) will not substantially change the nutritional value of raw milk or other benefits associated with raw milk consumption."

Raw milk advocates, such as the Weston A. Price Foundation, say that raw milk can be produced hygienically, and that it has health benefits that are destroyed in the pasteurization process. Research shows only very slight differences in the nutritional values of pasteurized and unpasteurized milk.

Three studies have found a statistically significant inverse relationship between consumption of raw milk and asthma and allergies. However, all of these studies have been performed in children living on farms and living a farming lifestyle, rather than comparing urban children living typical urban lifestyles and with typical urban exposures on the basis of consumption or nonconsumption of raw milk. Aspects of the overall urban vs. farming environment lifestyle have been suggested as having a role in these differences, and for this reason, the overall phenomenon has been named the "farm effect". A recent scientific review concluded that "most studies alluding to a possible protective effect of raw milk consumption do not contain any objective confirmation of the raw milk's status or a direct comparison with heat-treated milk. Moreover, it seems that the observed increased resistance seems to be rather related to the exposure to a farm environment or to animals than to raw milk consumption." For example, in the largest of these studies, exposure to cows and straw as well as raw milk were associated with lower rates of asthma, and exposure to animal feed storage rooms and manure with lower rates of atopic dermatitis; "the effect on hay fever and atopic sensitization could not be completely explained by the questionnaire items themselves or their diversity."

Before purified milk was adopted in the US, public health officials were concerned with cow milk transmission of bovine tuberculosis to humans with an estimated 10% of all tuberculosis cases in humans being attributed to milk consumption. Along with specific diseases, officials continue to be concerned about outbreaks. With the use of modern pasteurization and sanitation practices milk accounts for less than 1% of reported outbreaks from food and water consumption. As comparison, raw milk was associated with 25% of all disease outbreaks from food/water during the time before World War II in the U.S. From a public health stand point pasteurization has decreased the percentage of milk associated food/water borne outbreaks.

Outbreaks have occurred in the past from consuming food products made with raw milk. One of the potential pathogens in raw milk, "Listeria monocytogenes", can survive the pasteurization process and contaminate post-pasteurization environments. Milk and dairy products made with that milk then become recontaminated. Consistent contamination persists by bacteria survival in bio-films within the processing systems. One food item that has commonly used raw milk in its production in the past is cheese. Several different types of cheeses made with raw milk are consumed by a large portion of the United States population, including soft cheeses. Since Gouda cheese has a 60-day aging period prior to its consumption, it has previously been hypothesized that no bacteria would persist through that time. A review study published in the "Journal of Food Protection" showed that "E. coli" 0157:H7 has the ability to persist through the aging period of Gouda cheese. The study's evidence included three different outbreaks prior to 2013 associated with this specific strain of "E. coli" in Gouda cheese.

Between 2007 and 2016 there were 144 outbreaks connected to raw milk consumption in the United States. Because raw milk production skips the pasteurization process, the germs that are normally removed remain in the milk product. Exposure to raw milk containing harmful germs poses a threat of infection, resulting from bacteria including "Camplyobacter", "Cryptosporidium", "E. coli", "Listeria", and "Salmonella". Additionally, depending on the severity of infection, there may be further threat to human health. Infection has the potential to induce serious illness such as Guillain-Barré syndrome and Hemolytic Uremic Syndrome (HUS). Because of the vulnerability of developing and degrading immune systems, children, pregnant women, the elderly, and those who are immunocompromised are at a heightened risk of experiencing infection from raw milk consumption.

One study used mice to evaluate the difference in nutritional values between raw and pasteurized milk. Mice were separated into two groups: a pasteurized milk group and a raw milk group. Each group consisted of breeding pairs. The conclusion of the study measured no significant difference in weights of pasteurized to raw milk consuming mice. Birth weights were measured from each group and showed no significant differences between groups. Overall the study showed no measurable significant difference in nutritional value in growth and fertility of mice.

Regulation of the commercial distribution of packaged raw milk varies around the world. Some countries have complete bans, but many had partial bans that do not restrict the purchase of raw milk bought directly from the farmer. Raw milk is sometimes distributed through a program, in which the consumer owns a share in the dairy animal or the herd, and therefore can be considered to be consuming milk from their own animal, which is legal. Raw milk is sometimes marketed for animal or pet consumption, or for other uses such as soap making in places where sales for human consumption are prohibited.

Although milk consumption in Africa is fairly low compared to the rest of the world, in tribes where milk consumption is popular, such as the Maasai tribe, milk is typically consumed unpasteurized.

In rural areas of Asia where milk consumption is popular, milk is typically unpasteurized. In large cities of Asia, raw milk, especially from water buffalo, is typical. In most countries of Asia, laws prohibiting raw milk are nonexistent or rarely enforced.

The European Union requires that raw milk and products made with raw milk must be labeled to indicate this. Under EU hygiene rules, member states can prohibit or restrict the placing on the market of raw milk intended for human consumption. Also, European countries are free to add certain requirements. Usually special sanitary regulations and frequent quality tests (at least once per month) are mandatory.

Raw-milk cheeses make up about 18 percent of France's total cheese production, and are considered far superior to cheeses made from pasteurised milk. Many French cuisine traditionalists consider pasteurized cheeses almost a sacrilege. Many traditional French cheeses have solely been made from raw milk for hundreds of years. Unpasteurised cheese in France is the major source of staphylococcal food poisoning.

In Germany, packaged raw milk may be sold in shops under the name "Vorzugsmilch". The raw milk has to be packed before vending, with the necessary information (producer, durability, and special warnings) written on the product. The distribution license has stringent quality restrictions, and so just 80 farmers in Germany have one.

Unpackaged raw milk may only be sold under specific conditions. It must:

Packed raw milk is sold widely in all health food stores, large supermarkets, gourmet delis and delicatessen sections of department stores. Raw milk is legally sold in the entire country, and the same goes for raw milk cheeses, which are especially sought out and promoted by the health food and slow food movements.

Shops are not permitted to sell unpasteurised milk to consumers in Norway Sweden Finland and Denmark. All four countries allow limited "barn door" sales subject to strict controls. One distributor in Denmark is licensed to supply restaurants with raw milk from approved farms. Pasteurisation of milk became common practice in Denmark and Sweden in the mid-1880s.

Raw milk has been available from refrigerated milk vending machines ("mlekomati") all over the country since 2010. The milk sold in the machines is subject to stringent regular control.
As of 2018, raw milk is also available in shops.

Sales of raw drinking milk are prohibited in Scotland following a spate of deaths in 1983. While it is legal in England, Wales, and Northern Ireland, the only registered producers are in England. About 200 producers sell raw, or "green top" milk directly to consumers, either at the farm, at a farmers' market, or through a delivery service, as it is legal to supply unpasteurised raw milk directly to consumers, but illegal to be sold to a retail shop. The bottle must display the warning "this product has not been heat-treated and may contain organisms harmful to health", and the dairy must conform to higher hygiene standards than dairies producing only pasteurised milk.

The sale of raw milk directly to consumers is prohibited in Canada under the "Food and Drug Regulations" since 1991.

Provincial laws also forbid the sale and distribution of raw milk. For instance, Ontario's Health Protection and Promotion Act, subsection 18(1) reads: "No person shall sell, offer for sale, deliver or distribute milk or cream that has not been pasteurized or sterilized in a plant that is licensed under the Milk Act or in a plant outside Ontario that meets the standards for plants licensed under the Milk Act."

In January 2010, Michael Schmidt was found not guilty on 19 charges relating to the sale of raw milk in the Ontario Court of Justice. On appeal to the Ontario Court of Justice, that decision was overturned. Schmidt was convicted on thirteen counts and imposed fines totaling $9,150 and one year of probation. A subsequent appeal to the Ontario Court of Appeal was dismissed.

In British Columbia, Alice Jongerden and Michael Schmidt and Gordon Watson — persons involved in the operation of her raw milk dairy — attempted to avoid enforcement of a judgement against them under the Public Health Act by challenging the constitutionality of the legislation, which deems raw milk to be a hazardous product, on the grounds that it violated the Canadian Charter of Rights and Freedoms. This argument, and other defenses invoked by her and defendants in her business, was rejected in 2013 by the Supreme Court of British Columbia, which instead found Schmidt and Watson guilty of civil contempt, and sentenced them to a 3-month suspended sentence imprisonment with a probationary period of 1 year during which "Any repetition of this contempt... will trigger the imposed sentence imprisonment of 3 months." They were also charged special costs.

Meanwhile, Canada does permit the sale of raw milk cheeses that are aged over 60 days. In 2009, the province of Quebec modified regulations to allow raw milk cheeses aged less than 60 days provided stringent safeguards are met.

In the early 20th century many states allowed the sale of raw milk that was certified by a "medical milk commission", effectively allowing an alternative of extra inspection for pasteurization. Now most states impose restrictions on raw milk suppliers due to concerns about safety. Forty-three U.S. states allow sales of raw milk. Cow shares can be found, and raw milk purchased for animal consumption in many states where retail for human consumption is prohibited. The sale of raw milk cheese is permitted as long as the cheese has been aged for 60 days or more.

The FDA reports that, in 2002, consuming partially heated raw milk and raw milk products caused 200 Americans to become ill in some manner.

Many governmental officials and the majority of public health organizations hold to the need for pasteurization. Before pasteurization, many dairies, especially in cities, fed their cattle on low-quality food, and their milk was rife with dangerous bacteria. Pasteurizing it was the only way to make it safely drinkable. As pasteurization has been standard for many years, it is now widely assumed that raw milk is dangerous. The Cornell University Food Science Department has compiled data indicating that pathogenic microorganisms are present in between 0.87% and 12.6% of raw milk samples.

Proponents of raw milk (in the U.S.) advance two basic arguments for unpasteurized milk. They state that pasteurization destroys or damages some of the milk's nutrients, and that while pasteurization may kill dangerous bacteria, it also kills off good bacteria that raw milk supporters have stated to have health benefits. The United States Food and Drug administration has stated that this is false, and that pasteurizing milk does not destroy any of its nutritive value.

Proponents also invoke the benefits of direct-marketing when promoting the sale of raw milk. The ability of the farmer to eliminate the middle-man and sell directly to the consumer allows for greater profitability. Many manufacturers sell small-scale pasteurization equipment, thereby allowing farmers to both bypass the milk processors and sell pasteurized milk directly to the consumer. Additionally, some small U.S. dairies are now beginning to adopt low-temperature vat pasteurization. Advocates of low-temperature vat pasteurization note that it produces a product similar to raw milk in composition.

Alongside the ongoing empirical debate, food freedom advocates cite libertarian arguments in claiming a basic civil right of each person to weigh the risks and benefits in choosing the food one eats.

The sale of raw milk for drinking purposes is illegal in all states and territories in Australia, as is all raw milk cheese. This has been circumvented somewhat by selling raw milk as "bath milk". An exception to the cheese rule has been made recently for two Roquefort cheeses. There is some indication of share owning cows, allowing the "owners" to consume the raw milk, but also evidence that the government is trying to close this loophole.

On November 8, 2015, 4 year old Apu Khangura died of haemolytic uraemic syndrome, 7 other children became seriously ill, the Victorian government created new regulations which require producers to treat raw milk to reduce pathogens, or to make the product unpalatable to taste, such as making it bitter.

Raw milk for drinking and raw milk products can be made and sold in New Zealand, but are highly regulated to offset the pathogen risk. Producers of raw milk for sale to consumers must be registered. Raw milk must either be collected by the purchaser from the producer's farm or delivered to the purchaser's home.

Raw yak milk is allowed to ferment overnight to become yak butter. Some cheeses are produced with raw milk although local statutes vary regarding what if any health precautions must be followed such as aging cheese for a certain amount of time.

A thick mixture known as Syllabub was created by milkmaids squirting milk directly from a cow into a container of cider, beer, or other beverage.

Pasteurization is a sanitation process in which milk is heated briefly to a temperature high enough to kill pathogens, followed by rapid cooling. While different times and temperatures may be used by different processors, pasteurization is most commonly achieved with heating to 161 degrees Fahrenheit (71.7 degrees Celsius) for 15 seconds. Milk is tested following pasteurization to confirm that bacteria have been killed to an acceptable level. Pasteurization kills pathogenic bacteria which occasionally may be present in milk, including those causing tuberculosis ("Mycobacterium bovis"), listeriosis ("Listeria monocytogenes"), Q fever ("Coxiella burnetii"), brucellosis ("Brucella"), campylobacteriosis ("Campylobacter"), salmonellosis ("Salmonella"), and several other foodborne illnesses (e.g., ). Pasteurization may not kill some resistant bacteria, which can eventually cause souring and spoilage of fresh milk. UHT pasteurization (Ultra High Temperature) is a more extreme form of pasteurization heating milk to a temperature high enough to kill spoilage organisms also.

United States raw milk debate

The United States raw milk debate concerns issues of food safety and claimed health benefits of raw (un-pasteurized, un-homogenized) milk, and whether authorities responsible for regulating food safety should prohibit sale of raw milk for consumption.

Raw milk makes up a small proportion of US general population milk consumption. However, some claim the demand for raw milk has "considerably increased in recent years". Raw milk advocates claim a variety of health benefits attributable to untreated dairy products; government officials and scientific researchers stress that there are substantial food safety risks associated with raw milk, and that claims of health benefits provided by raw milk are unsupported by scientific evidence.

Unprocessed milk consists of globules of milk fat suspended in a watery base containing dissolved proteins, sugars, vitamins, and minerals. If the globules are large enough, as with unprocessed milk from cows, the fat globules float upwards until they form a distinct cream layer at the top. Some animals, such as goats, produce smaller fat globules that remain mixed unless mechanically separated by centrifugation.

Homogenization is a process that reduces the size of fat globules by forcing pressurized, hot milk through small holes, causing turbulence that breaks up the larger fat globules so that they remain suspended rather than separating in a cream layer at the top. The purpose of homogenization is to make milk more convenient to process, store and consume, eliminating the need to shake or stir the milk container to remix the separated cream layer and increasing the shelf-life of the product.

Those opposed to homogenization argue that decreasing the size of fat globules may have unhealthy effects, including allowing steroid and protein hormones to bypass normal digestion and increase their levels in the body. Concerns that uptake of the protein xanthine oxidase is increased by homogenization, leading to hardening of the arteries (atherosclerosis), were raised in the 1970s. Subsequent research "failed to substantiate, and in many cases has refuted" a plausible effect of xanthine oxidase from homogenized milk on cardiovascular disease.

Scientific studies are somewhat limited but do not currently support claims that milk homogenization affects the development of atherosclerosis, coronary heart disease, milk allergy and milk intolerance, Type I diabetes or Type II diabetes.

Pasteurization is widely accepted to improve the safety of milk products by reducing the exposure to pathogens. Opponents of pasteurization argue that unpasteurized milk has benefits associated with superior taste, nutritional qualities and certain health benefits over pasteurized milk. While pasteurization of milk kills off bacterial pathogens, other bacteria species with possible health benefits are also destroyed. Pasteurization of cow's milk destroys any potential pathogens and increases the shelf life. During pasteurization, however, these lactic acid bacteria are mostly destroyed. A 2009 systematic review of the food safety of unpasteurized milk concluded that science-based data to substantiate claims of health benefits "are lacking or do not exist" and the risks associated with disease outbreaks as a result of raw milk consumption are "considerably higher".

Pasteurization was first used in the United States in the 1890s after the discovery of germ theory to control the hazards of highly contagious bacterial diseases, including bovine tuberculosis and brucellosis, that could be easily transmitted to humans through the drinking of raw milk. Initially after the scientific discovery of bacteria, no product testing was available to determine if a farmer's milk was safe or infected, so all milk had to be treated as potentially contagious. After the first test was developed, some farmers actively worked to prevent their infected animals from being killed and removed from food production, or would falsify the test results so that their animals would appear to be free of infection.

In the United States, milk pasteurization became "widespread" in the 1920s and it was considered "one of the major breakthroughs in public health". In 1924, "Grade A Pasteurization" became recommended federal policy, but interstate commerce of unpasteurized dairy products was only limited via federal legislation in 1987.

In 2009, 29 U.S. states allowed sales of raw milk in some form. In other parts of the world, raw milk can often be bought directly from the farmer. Arizona, Utah, California and Washington allow raw milk sales in retail stores with appropriate warning labeling. As of May 2010, Massachusetts only allows direct sales from farm to consumer, resulting in "buying clubs" where consumers pool transportation resources to obtain raw milk more conveniently. In April 2013, the State of North Dakota passed a law that authorizes the use of herd shares.

In late 2007, the debate received media attention in California, where limits on the bacterial counts legally allowed in commercial raw milk came up for legislative review. Reuters named the raw milk debate as first on a list of the top eight health issues of 2008. The FDA has also offered financial assistance to state departments of health to help reduce raw milk consumption.

Pasteurization is credited with dramatically reducing pathogens found in milk. This improves the shelf-life and safety of the processed milk. Advocates of drinking raw milk claim various health benefits they attribute to raw milk that are lost in the pasteurization process, and claim that raw milk can be produced as hygienically as pasteurized milk. Raw milk advocates may go as far as to claim that untreated milk is a "miracle cure" for illnesses such as asthma or gastrointestinal disorders. A 2006 systematic review of infections associated with raw milk contends that pasteurized milk is substantially safer than raw milk, and comparably nutritious to raw milk, therefore there is no scientific reason for choosing raw milk products. Similarly, a recent review authored by the Belgian Federal Agency for the Safety of the Food Chain and experts from Belgian universities and institutions concluded that "raw milk poses a realistic health threat due to a possible contamination with human pathogens. It is therefore strongly recommended that milk should be heated before consumption. With the exception of an altered organoleptic [flavor] profile, heating (in particularly ultra high temperature and similar treatments) will not substantially change the nutritional value of raw milk or other benefits associated with raw milk consumption."

Pasteurization opponents say that raw milk contains bacteria beneficial to the human digestive system, but pasteurization is not selective and affects all bacteria whether beneficial or infectious. These bacteria include species considered to be probiotics, such as "Lactobacillus acidophilus", useful for the culturing of yogurt and cheese. Fermented milk products with levels of "L. acidophilus" significantly higher than those found in raw milk have been associated with decreased incidence of pediatric diarrhea, decreased levels of toxic amines in the blood of dialysis patients with small bowel bacterial overgrowth, aided lactose digestion in lactose-intolerant subjects, and a reduction in coronary heart disease risks. However, food scientists and FDA officials maintain that such "good bacteria" can be found in pasteurized products, including yogurt, and argue that the destruction of pathogens far outweighs any proposed benefit to keeping the beneficial microbes alive.

According to a 2009 review, milkborne disease outbreaks made up approximately 25% of all food and water contamination disease outbreaks in 1938; pasteurization is largely credited for a dramatic decrease in milkborne disease outbreaks, which made up less than 1% of food and water contamination disease outbreaks by 2005.

According to the Center for Disease Control and Prevention, more than 300 people in the United States got sick from drinking raw milk or eating cheese made from raw milk in 2001, and nearly 200 became ill from these products in 2002. "Drinking raw milk or eating raw milk products is like playing Russian roulette with your health," says John Sheehan, director of the Food and Drug Administration's Division of Dairy and Egg Safety. "We see a number of cases of food-borne illness every year related to the consumption of raw milk."

In 2006, the California Department of Food and Agriculture temporarily quarantined milk and cream from Organic Pastures, California's largest raw milk producer, after four children were stricken with bacterial illness. The department determined that the common link in all four cases "was consumption of raw milk or raw colostrum from Organic Pastures in the week prior to symptom onset."

Milk collected or stored in unsanitary conditions may harbor a host of disease-causing organisms (pathogens), such as "tuberculosis" (Mycobacterium bovis), the bacteria "Campylobacter" (Campylobacteriosis), "Escherichia" E. coli O157:H7), "Listeria" (Listeriosis), "Salmonella" (Salmonellosis), "Yersinia" (Yersinia enterocolitica), and "Brucella" (Brucellosis). Pasteurization consistently removes all of these pathogens, though they can be reintroduced if the product is handled carelessly. Thus dairy farms that pasteurize their milk can have unsanitary facilities without the attendant outbreaks of disease that would occur if a raw milk dairy kept its herds in similar unsanitary conditions.

People with weakened immune systems, such as elderly, children, and those with certain diseases or conditions, are most at risk for severe infections from pathogens that can contaminate raw milk. In pregnant women, "Listeria monocytogenes"-caused illness can result in miscarriage, fetal death, or illness or death of a newborn infant, and "Escherichia coli" (E. coli) infection has been linked to hemolytic uremic syndrome, a condition that can cause kidney failure and death. Other groups, such as the Center for Food Safety and Applied Nutrition and American Academy of Pediatrics, also warn that raw milk is dangerous, especially for children.

The Centers for Disease Control (CDC) cite numerous cases of serious or fatal infections caused by raw milk, with "E. coli" O157:H7 being the most important because it can cause hemolytic-uremic syndrome, a life-threatening condition. In a CDC report, numerous cases were traced to raw milk from a cow-share program in Cowlitz County, Washington. After five children were hospitalized, a court order was issued to bring the farm into compliance. In 2007, Kansas State University published a list of outbreaks associated with consuming raw milk or dairy products and an article about the investigation of raw milk outbreaks.

The Weston A. Price Foundation has been active in promoting raw milk with its "Real Milk" campaign. The organization claims that of 15 milkborne disease outbreaks cited by the FDA, not a single one demonstrated that pasteurization would have fixed the problem, that 93% lacked either a valid statistical correlation with raw milk or a positive sample, and half lacked both; they further claimed that, even with the FDA's numbers, raw milk was no more dangerous than deli meats. In response, the director of the FDA's division of plant- and dairy-food safety, John Sheehan, called the organization's claims on the health benefits and safety of raw milk "false, devoid of scientific support, and misleading to consumers".

In 2008, scientists discovered that raw milk contains more species of bacteria than previously thought, and identified "Chryseobacterium oranimense" as well as "C. haifense" and "C. bovis", but the amount found in raw milk has not been proven harmful.

While causation has not been determined, researchers in 2015 found that 59% of people with breast cancer had bovine leukemia virus (BLV) in their breast cancer samples, compared to the virus being found in only 29% of tissue samples of people who had never had breast cancer. BLV is common, spread by blood and milk in cows, and has been found in 100% of bulk milk tanks in dairy operations with over 500 cows. Consuming unpasteurized milk or under cooked meats could be pathways for human exposure to BLV.

In November 2017, the US Centers for Disease Control and Prevention recommended medical treatment for anyone who had, within the previous six months, consumed raw milk products from Udder Milk, a New Jersey-based cooperative. An antibiotic resistant strain of Brucella abortus, which can cause the disease Brucellosis, was detected in at least one person who drank raw milk from the co-op.

Advocates of drinking raw milk claim raw milk contains desirable substances, such as enzymes, that cannot survive the heating process and may be destroyed during pasteurization; specifically, immunoglobulins and the enzymes lipase and phosphatase, which are inactivated by heat, are believed to be beneficial. In contrast, food scientists and FDA officials assert that most "beneficial" enzymes survive pasteurization; that those few enzymes that are present in raw milk and denatured in pasteurized milk are ultimately degraded in the low pH environment of the stomach anyway; and that the enzymes present in milk are not used by humans to metabolize nutrients.

Pasteurization does lead to decreased levels of several vitamins, but only approximately 0–10%. Research shows only very slight differences in the nutritional values of pasteurized and unpasteurized milk. Raw milk contains very little vitamin D, which is added to processed milk.

Three studies have found a statistically significant inverse relationship between consumption of raw milk and asthma and allergies. However, all of these studies have been performed in children living on farms and living a farming lifestyle, rather than comparing urban children living typical urban lifestyles and with typical urban exposures who do or do not consume raw milk, so it is likely that other aspects of the overall urban vs. farming environment lifestyle play a role in these effects; for this reason, the overall phenomenon is termed the "farm effect." In the largest of these studies, exposure to cows and straw as well as raw milk were associated with lower rates of asthma, and exposure to animal feed storage rooms and manure with lower rates of atopic dermatitis. A recent scientific review concluded that “most studies alluding to a possible protective effect of raw milk consumption do not contain any objective confirmation on the raw milk status or a direct comparison with heat-treated milk. Moreover, it seems that the observed increased resistance seems to be rather related to the exposure to a farm environment or to animals than to raw milk consumption.”

Many raw milk consumers cite a preference for the taste of raw milk products.

The Raw Milk Cheesemakers Association hold that cheese produced from raw milk have distinctive complexity and depth of flavor absent from pasteurized-milk cheeses.

The FDA considers hard, aged cheese, such as parmesan and cheddar, made from raw milk to be generally safe for consumption; soft cheese made from raw milk is considered unsafe. These types of cheese are currently legally sold if aged for 60 days or more. Over this period, the salt and acid characteristics of aging cheese generally eliminate the growth of pathogenic bacteria.

Raw milk advocates cite libertarian and personal choice arguments against government interference concerning the sale of raw milk. Some advocates feel resentment towards the government's efforts in limiting the distribution and consumption of raw milk, seeing their actions as a personal choice that is not harmful to anyone else. Raw milk activism can be associated with alternative medicine and anti-regulatory activism.

The methods of determining Grade A milk quality are well-established and outlined in the FDA Grade A Pasteurized Milk Ordinance. These grades are typically related to a measurement known as the somatic cell count (SCC) and the bacteria plate count. Generally a lower somatic cell count indicates better animal health, while the bacteria plate count indicates improved equipment sanitation.

Somatic cells originate only from inside the animal's udder, while bacteria are usually from external contamination, such as insufficient cleaning of the milk transport equipment or insufficient external cleansing of the cow’s udder and teats prior to milking. Milking equipment can also be accidentally knocked or kicked off an animal onto the floor, and contaminants on the barn floor can be sucked into the milk line by the system vacuum. A filter sock or filter disk in the pipeline prevents large particulate contaminants from entering the milk bulk tank, but cannot remove bacterial contamination once it has occurred.

For example, as defined by the state of Indiana’s administrative code, Grade A milk shall meet the following standards:Milk not meeting these standards shall be designated as undergrade. Undergrade milk may not be sold for human consumption or processing into products for human consumption.

As established, these measurements are taken daily from the milk bulk tank and not from individual cows. This is because testing of individual animals at each milking would be expensive, but it also means that milk from a sick cow is diluted and averaged down by the healthy animals. Greater bulk tanks at very great commercial farms are accommodating of more sick animals in the herd, without the sick animals affecting the overall milk quality rating.

As discussed in the paper "Guidelines for Using the DHI Somatic Cell Count Program"

Bacteria in milk can come from sources other than the animal. Over time the milking pipeline and equipment can become coated with residues such as "milkstone" which are not removed by standard detergents and require periodic flushing of equipment with high strength corrosives. Automatic washing equipment for the bulk tank may not effectively clean all interior surfaces, and does not clean the exterior of the bulk tank at all.

Some buyers award producers for having the lowest SCC but this does not also lead to an increased payment for the milk quality, so there is no incentive to strive for anything more than meeting the basic grade A SCC rating.

United States raw milk debate

The United States raw milk debate concerns issues of food safety and claimed health benefits of raw (un-pasteurized, un-homogenized) milk, and whether authorities responsible for regulating food safety should prohibit sale of raw milk for consumption.

Raw milk makes up a small proportion of US general population milk consumption. However, some claim the demand for raw milk has "considerably increased in recent years". Raw milk advocates claim a variety of health benefits attributable to untreated dairy products; government officials and scientific researchers stress that there are substantial food safety risks associated with raw milk, and that claims of health benefits provided by raw milk are unsupported by scientific evidence.

Unprocessed milk consists of globules of milk fat suspended in a watery base containing dissolved proteins, sugars, vitamins, and minerals. If the globules are large enough, as with unprocessed milk from cows, the fat globules float upwards until they form a distinct cream layer at the top. Some animals, such as goats, produce smaller fat globules that remain mixed unless mechanically separated by centrifugation.

Scientific studies are somewhat limited but do not currently support claims that milk homogenization affects the development of atherosclerosis, coronary heart disease, milk allergy and milk intolerance, Type I diabetes or Type II diabetes.

In the United States, milk pasteurization became "widespread" in the 1920s and it was considered "one of the major breakthroughs in public health". In 1924, "Grade A Pasteurization" became recommended federal policy, but interstate commerce of unpasteurized dairy products was only limited via federal legislation in 1987.

In late 2007, the debate received media attention in California, where limits on the bacterial counts legally allowed in commercial raw milk came up for legislative review. Reuters named the raw milk debate as first on a list of the top eight health issues of 2008. The FDA has also offered financial assistance to state departments of health to help reduce raw milk consumption.

According to a 2009 review, milkborne disease outbreaks made up approximately 25% of all food and water contamination disease outbreaks in 1938; pasteurization is largely credited for a dramatic decrease in milkborne disease outbreaks, which made up less than 1% of food and water contamination disease outbreaks by 2005.

In 2006, the California Department of Food and Agriculture temporarily quarantined milk and cream from Organic Pastures, California's largest raw milk producer, after four children were stricken with bacterial illness. The department determined that the common link in all four cases "was consumption of raw milk or raw colostrum from Organic Pastures in the week prior to symptom onset."

In 2008, scientists discovered that raw milk contains more species of bacteria than previously thought, and identified "Chryseobacterium oranimense" as well as "C. haifense" and "C. bovis", but the amount found in raw milk has not been proven harmful.

In November 2017, the US Centers for Disease Control and Prevention recommended medical treatment for anyone who had, within the previous six months, consumed raw milk products from Udder Milk, a New Jersey-based cooperative. An antibiotic resistant strain of Brucella abortus, which can cause the disease Brucellosis, was detected in at least one person who drank raw milk from the co-op.

Pasteurization does lead to decreased levels of several vitamins, but only approximately 0–10%. Research shows only very slight differences in the nutritional values of pasteurized and unpasteurized milk. Raw milk contains very little vitamin D, which is added to processed milk.

Many raw milk consumers cite a preference for the taste of raw milk products.

The Raw Milk Cheesemakers Association hold that cheese produced from raw milk have distinctive complexity and depth of flavor absent from pasteurized-milk cheeses.

The FDA considers hard, aged cheese, such as parmesan and cheddar, made from raw milk to be generally safe for consumption; soft cheese made from raw milk is considered unsafe. These types of cheese are currently legally sold if aged for 60 days or more. Over this period, the salt and acid characteristics of aging cheese generally eliminate the growth of pathogenic bacteria.

Raw milk advocates cite libertarian and personal choice arguments against government interference concerning the sale of raw milk. Some advocates feel resentment towards the government's efforts in limiting the distribution and consumption of raw milk, seeing their actions as a personal choice that is not harmful to anyone else. Raw milk activism can be associated with alternative medicine and anti-regulatory activism.

The methods of determining Grade A milk quality are well-established and outlined in the FDA Grade A Pasteurized Milk Ordinance. These grades are typically related to a measurement known as the somatic cell count (SCC) and the bacteria plate count. Generally a lower somatic cell count indicates better animal health, while the bacteria plate count indicates improved equipment sanitation.

For example, as defined by the state of Indiana’s administrative code, Grade A milk shall meet the following standards:Milk not meeting these standards shall be designated as undergrade. Undergrade milk may not be sold for human consumption or processing into products for human consumption.

As established, these measurements are taken daily from the milk bulk tank and not from individual cows. This is because testing of individual animals at each milking would be expensive, but it also means that milk from a sick cow is diluted and averaged down by the healthy animals. Greater bulk tanks at very great commercial farms are accommodating of more sick animals in the herd, without the sick animals affecting the overall milk quality rating.

As discussed in the paper "Guidelines for Using the DHI Somatic Cell Count Program"

Bacteria in milk can come from sources other than the animal. Over time the milking pipeline and equipment can become coated with residues such as "milkstone" which are not removed by standard detergents and require periodic flushing of equipment with high strength corrosives. Automatic washing equipment for the bulk tank may not effectively clean all interior surfaces, and does not clean the exterior of the bulk tank at all.

Some buyers award producers for having the lowest SCC but this does not also lead to an increased payment for the milk quality, so there is no incentive to strive for anything more than meeting the basic grade A SCC rating.

Developed countries adopted milk pasteurization to prevent such disease and loss of life, and as a result milk is now considered a safer food. A traditional form of pasteurization by scalding and straining of cream to increase the keeping qualities of butter was practiced in Great Britain in the 18th century and was introduced to Boston in the British Colonies by 1773, although it was not widely practiced in the United States for the next 20 years. Pasteurization of milk was suggested by Franz von Soxhlet in 1886. In the early 20th century, Milton Joseph Rosenau established the standards – i.e. low-temperature, slow heating at for 20 minutes – for the pasteurization of milk while at the United States Marine Hospital Service, notably in his publication of "The Milk Question" (1912). States in the U.S. soon began enacting mandatory dairy pasteurization laws, with the first in 1947, and in 1973 the U.S. federal government required pasteurization of milk used in any interstate commerce.

Pasteurization

Pasteurization or pasteurisation is a process in which certain packaged and non-packaged foods (such as milk and fruit juice) are treated with mild heat, usually less than, to eliminate pathogens and extend shelf life. The process is intended to sterilize foods by destroying or inactivating organisms that contribute to spoilage, including vegetative bacteria but not bacterial spores.

The process was named after the French scientist Louis Pasteur, whose research in the 1880s demonstrated that thermal processing would inactivate unwanted microorganisms in wine. Spoilage enzymes are also inactivated during pasteurization. Today, pasteurization is used widely in the dairy industry and other food processing industries to achieve food preservation and food safety.

Most liquid products are heat treated in a continuous system where heat can be applied using a plate heat exchanger and/or the direct or indirect use of hot water and steam. Due to the mild heat, there are minor changes to the nutritional quality and sensory characteristics 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 foods.

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

Much later, in 1768, Italian priest and scientist Lazzaro Spallanzani's research proved a product could be made "sterile" after thermal processing. Spallanzani boiled meat broth for one hour, sealed the container immediately after boiling, and noticed that the broth did not spoil and was free from microorganisms. In 1795, a Parisian chef and confectioner named Nicolas Appert began experimenting with ways to preserve foodstuffs, succeeding with soups, vegetables, juices, dairy products, jellies, jams, and syrups. He placed the food in glass jars, sealed them with cork and sealing wax and placed them in boiling water. In that same year, the French military offered a cash prize of 12,000 francs for a new method to preserve food. After some 14 or 15 years of experimenting, Appert submitted his invention and won the prize in January 1810. Later that year, Appert published "L'Art de conserver les substances animales et végétales" (or "The Art of Preserving Animal and Vegetable Substances"). This was the first cookbook of its kind on modern food preservation methods.

"La Maison Appert" (), in the town of Massy, near Paris, became the first food-bottling factory in the world, preserving a variety of foods in sealed bottles. Appert's method was to fill thick, large-mouthed glass bottles with produce of every description, ranging from beef and fowl to eggs, milk and prepared dishes. He left air space at the top of the bottle, and the cork would then be sealed firmly in the jar by using a vise. The bottle was then wrapped in canvas to protect it while it was dunked into boiling water and then boiled for as much time as Appert deemed appropriate for cooking the contents thoroughly. Appert patented his method, sometimes called "appertisation" in his honor.

Appert's method was so simple and workable that it quickly became widespread. In 1810, British inventor and merchant Peter Durand, also of French origin, patented his own method, but this time in a tin can, so creating the modern-day process of canning foods. In 1812, Englishmen Bryan Donkin and John Hall purchased both patents and began producing preserves. Just a decade later, Appert's method of canning had made its way to America. Tin can production was not common until the beginning of the 20th century, partly because a hammer and chisel were needed to open cans until the invention of a can opener by Robert Yeates in 1855.

A less aggressive method was developed by French chemist Louis Pasteur during an 1864 summer holiday in Arbois. To remedy the frequent acidity of the local aged wines, he found out experimentally that it is sufficient to heat a young wine to only about for a short time to kill the microbes, and that the wine could subsequently be aged without sacrificing the final quality. In honour of Pasteur, this process became known as "pasteurization". Pasteurization was originally used as a way of preventing wine and beer from souring, and it would be many years before milk was pasteurized. In the United States in the 1870s, it was common for milk to contain substances intended to mask spoilage before milk was regulated.

Milk is an excellent medium for microbial growth, and when it is stored at ambient temperature bacteria and other pathogens soon proliferate. The US Centers for Disease Control (CDC) says improperly handled raw milk is responsible for nearly three times more hospitalizations than any other food-borne disease source, making it one of the world's most dangerous food products. Diseases prevented by pasteurization can include tuberculosis, brucellosis, diphtheria, scarlet fever, and Q-fever; it also kills the harmful bacteria "Salmonella", "Listeria", "Yersinia", "Campylobacter", "Staphylococcus aureus", and "", among others.

Prior to industrialization, dairy cows were kept in urban areas to limit the time between milk production and consumption, hence the risk of disease transmission via raw milk was reduced. As urban densities increased and supply chains lengthened to the distance from country to city, raw milk (often days old) became recognized as a source of disease. For example, between 1912 and 1937, some 65,000 people died of tuberculosis contracted from consuming milk in England and Wales alone. Because tuberculosis has a long incubation period in humans, it was difficult to link unpasteurized milk consumption with the disease. In 1892, chemist Earnest Lederle experimentally inoculated milk from tuberculosis-diseased cows into guinea pigs, which caused them to develop the disease. In 1910, Lederle, then in the role of Commissioner of Health, introduced mandatory pasteurization of milk in New York City.

The shelf life of refrigerated pasteurized milk is greater than that of raw milk. For example, high-temperature, short-time (HTST) pasteurized milk typically has a refrigerated shelf life 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), it can even be stored non-refrigerated for up to 9 months.

According to the Centers for Disease Control, between 1998 and 2011, 79% of dairy-related disease outbreaks were due to raw milk or cheese products. They report 148 outbreaks and 2,384 illnesses (with 284 requiring hospitalization), as well as two deaths due to raw milk or cheese products during the same time period.

Pasteurization is a mild heat treatment of liquid foods (both packaged and unpackaged) where products are typically heated to below 100 °C. The heat treatment and cooling process are designed to inhibit 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 duration of shelf life. Parameters also take into account nutritional and sensory qualities that are sensitive to heat.

In acidic foods (pH <4.6), such as fruit juice and beer, the heat treatments are designed to inactivate enzymes (pectin methylesterase and polygalacturonase in fruit juices) and destroy spoilage microbes (yeast and lactobacillus). Due to the low pH of acidic foods, pathogens are unable to grow. The shelf-life is thereby extended several weeks. In less acidic foods (pH >4.6), such as milk and liquid eggs, the heat treatments are designed to destroy pathogens and spoilage organisms (yeast and molds). Not all spoilage organisms are destroyed under pasteurization parameters, thus subsequent refrigeration is necessary.

Food can be pasteurized in two ways: either before or after being packaged into containers. When food is packaged in glass, hot water is used to lower the risk of thermal shock. Plastics and metals are also used to package foods, and these are generally pasteurized with steam or hot water since the risk of thermal shock is low.

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

Shell or tube heat exchangers are designed for the pasteurization of Non-Newtonian foods such as dairy products, tomato ketchup and baby foods. A tube heat exchanger is made up of concentric stainless steel tubes. Food passes through the inner tube while the heating/cooling medium is circulated through the outer or inner tube.

The benefits of using a heat exchanger to pasteurize non-packaged foods versus pasteurizing foods in containers are:

After being heated in a heat exchanger, the product flows through a hold tube for a set period of time to achieve the required treatment. If pasteurization temperature or time is not achieved, a flow diversion valve is utilized to divert under-processed product back to the raw product tank. If the product is adequately processed, it is cooled in a heat exchanger, then filled.

High-temperature short-time (HTST) pasteurization, such as that used for milk ( for 15 seconds) ensures safety of milk and provides a refrigerated shelf life of approximately two weeks. In ultra-high-temperature (UHT) pasteurization, milk is pasteurized at for 1–2 seconds, which provides the same level of safety, but along with the packaging, extends shelf life to three months under refrigeration.

Direct microbiological techniques are the ultimate measurement of pathogen contamination, but these are costly and time-consuming, which means that products have a reduced shelf-life by the time pasteurization is verified.

As a result of the unsuitability of microbiological techniques, milk pasteurization efficacy is typically monitored by checking for the presence of alkaline phosphatase, which is denatured by pasteurization. Destruction of alkaline phosphatase ensures the destruction of common milk pathogens. Therefore, the presence of alkaline phosphatase is an ideal indicator of pasteurization efficacy. For liquid eggs, the effectiveness of the heat treatment is measured by the residual activity of α-amylase.

During the early 20th century, there was no robust knowledge of what time and temperature combinations would inactivate pathogenic bacteria in milk, and so a number of different pasteurization standards were in use. By 1943, both HTST pasteurization conditions of for 15 seconds, as well as batch pasteurization conditions of for 30 minutes, were confirmed by studies of the complete thermal death (as best as could be measured at that time) for a range of pathogenic bacteria in milk. Complete inactivation of "Coxiella burnetii" (which was thought at the time to cause Q fever by oral ingestion of infected milk) as well as of "Mycobacterium tuberculosis" (which causes tuberculosis) were later demonstrated. For all practical purposes, these conditions were adequate for destroying almost all yeasts, molds, and common spoilage bacteria and also for ensuring adequate destruction of common pathogenic, heat-resistant organisms. However, the microbiological techniques used until the 1960s did not allow for the actual reduction of bacteria to be enumerated. Demonstration of the extent of inactivation of pathogenic bacteria by milk pasteurization came from a study of surviving bacteria in milk that was heat-treated after being deliberately spiked with high levels of the most heat-resistant strains of the most significant milk-borne pathogens.

The mean log reductions and temperatures of inactivation of the major milk-borne pathogens during a 15-second treatment are:

The Codex Alimentarius "Code of Hygienic Practice for Milk" notes that milk pasteurization is designed to achieve at least a 5 log reduction of "Coxiella burnetii". The Code also notes that: “The minimum pasteurization conditions are those having bactericidal effects equivalent to heating every particle of the milk to 72°C for 15 seconds (continuous flow pasteurization) or 63°C for 30 minutes (batch pasteurization)” and that “To ensure that each particle is sufficiently heated, the milk flow in heat exchangers should be turbulent, "i.e". the Reynolds number should be sufficiently high.” The point about turbulent flow is important because simplistic laboratory studies of heat inactivation that use test tubes, without flow, will have less bacterial inactivation than larger-scale experiments that seek to replicate conditions of commercial pasteurization.

As a precaution, modern HTST pasteurization processes must be designed with flow-rate restriction as well as divert valves which ensure that the milk is heated evenly and that no part of the milk is subject to a shorter time or a lower temperature. It is common for the temperatures to exceed 72 °C by 1.5 °C or 2 °C.

Because of its mild heat treatment, pasteurization increases the shelf-life by a few days or weeks. However, this mild heat also means there are only minor changes to heat-labile vitamins in the foods.

According to a systematic review and meta-analysis, it was found that pasteurization appeared to reduce concentrations of vitamins B12 and E, but it also increased concentrations of vitamin A. Apart from meta-analysis, it is not possible to draw conclusions about the effect of pasteurization on vitamins A, B12, and E based merely on consultation of the vast literature available. Milk is not an important source of vitamins B12 or E in the North American diet, so the effects of pasteurization on the adult daily intake of these vitamins is negligible. However, milk is considered an important source of vitamin A, and because pasteurization appears to increase vitamin A concentrations in milk, the effect of milk heat treatment on this vitamin is a not a major public health concern. Results of meta-analyses reveal that pasteurization of milk leads to a significant decrease in vitamin C and folate, but milk is also not an important source of these vitamins. A significant decrease in vitamin B2 concentrations was found after pasteurization. Vitamin B2 is typically found in bovine milk at concentrations of 1.83 mg/liter. Because the recommended daily intake for adults is 1.1 mg/day, milk consumption greatly contributes to the recommended daily intake of this vitamin. With the exception of B2, pasteurization does not appear to be a concern in diminishing the nutritive value of milk because milk is often not a primary source of these studied vitamins in the North American diet.

Pasteurization also has a small but measurable effect on the sensory attributes of the foods that are processed. In fruit juices, pasteurization may result in loss of volatile aroma compounds. Fruit juice products undergo a deaeration process prior to pasteurization that may be responsible for this loss. Deaeration also minimizes the loss of nutrients like vitamin C and carotene. To prevent the decrease in quality resulting from the loss in volatile compounds, volatile recovery, though costly, can be utilized to produce higher-quality juice products.

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

In milk, the color difference between pasteurized and raw milk is related to the homogenization step that takes place prior to pasteurization. Before pasteurization, milk is homogenized to separate the solids (fat) from the liquid, which results in the pasteurized milk having a whiter appearance compared to raw milk. For vegetable products, color degradation is dependent on the temperature conditions and the duration of heating.

Pasteurization may result in some textural loss as a result of enzymatic and non-enzymatic transformations in the structure of pectin if the processing temperatures are too high as a result. However, with mild heat treatment pasteurization, tissue softening in the vegetables that causes textural loss is not of concern as long as the temperature does not get above.

Other thermal and non-thermal processes have been developed to pasteurize foods as a way of reducing the effects on nutritional and sensory characteristics of foods and preventing degradation of heat-labile nutrients. Pascalization or high pressure processing (HPP) and pulsed electric field (PEF) are examples of these non-thermal pasteurization methods that are currently commercially utilized.

Microwave volumetric heating (MVH) is the newest available pasteurization technology. It uses microwaves to heat liquids, suspensions, or semi-solids in a continuous flow. Because MVH delivers energy evenly and deeply into the whole body of a flowing product, it allows for gentler and shorter heating, so that almost all heat-sensitive substances in the milk are preserved.