Pasteurization
In food processing, pasteurization is a process of food preservation in which packaged foods are treated with mild heat, usually to less than, to eliminate pathogens and extend shelf life. Pasteurization either destroys or deactivates microorganisms and enzymes that contribute to food spoilage or the risk of disease, including vegetative bacteria, but most bacterial spores survive the process.
Pasteurization is named after French microbiologist Louis Pasteur, whose research in the 1860s demonstrated that thermal processing would deactivate 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 for food preservation and food safety.
By the year 1999, most liquid products were heat treated in a continuous system where heat was applied using a heat exchanger 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 and pulsed electric field are non-thermal processes that are also used to pasteurize foods.
History
Heating wine for preservation 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.In 1768, research by Italian priest and scientist Lazzaro Spallanzani proved that 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. This was the first cookbook 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 filled 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, the British inventor and merchant Peter Durand, also of French origin, patented his method, but this time in a tin can, so creating the modern-day process of canning foods. In 1812, the Englishmen Bryan Donkin and John Hall purchased both patents and began producing preserves. A decade later, Appert's canning method had come 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 honor of Pasteur, this process is 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, before milk was regulated, it was common for milk to contain substances intended to mask spoilage.
Milk
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 and Prevention 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 include tuberculosis, brucellosis, diphtheria, scarlet fever, and Q-fever; it also kills the harmful bacteria Salmonella, Listeria, Yersinia, Campylobacter, Staphylococcus aureus, and Escherichia coli O157:H7, among others.Before 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 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 Ernst 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.
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 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. 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.
The shelf life of refrigerated pasteurized milk is greater than that of raw milk. For example, high-temperature, short-time 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 is combined with sterile handling and container technology, 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 in the United States were due to raw milk or cheese products. They report 148 outbreaks and 2,384 illnesses, as well as two deaths due to raw milk or cheese products during the same period.
Medical equipment
Medical equipment, notably respiratory and anesthesia equipment, is often disinfected using hot water, as an alternative to chemical disinfection. The temperature is raised to for 30 minutes. More thorough sterilization can be performed at higher temperatures and pressures in an autoclave.Pasteurization process
Pasteurization is a mild heat treatment of liquid foods where products are typically heated to below. The heat treatment and cooling process are designed to inhibit a phase change in the product. The acidity of the food determines the parameters 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, such as fruit juice and beer, the heat treatments are designed to inactivate enzymes and destroy spoilage microbes. Due to the low pH of acidic foods, pathogens cannot grow. The shelf-life is thereby extended by several weeks. In less acidic foods, such as milk and liquid eggs, heat treatments are designed to destroy pathogens and spoilage organisms. Not all spoilage organisms are destroyed under pasteurization parameters, so subsequent refrigeration is necessary.
High-temperature short-time pasteurization, such as that used for milk ensures the safety of milk and provides a refrigerated shelf life of approximately two weeks. In ultra-high-temperature pasteurization, milk is pasteurized at for 1–2 seconds. Along with special packaging this extends shelf life to three months without refrigeration.
Equipment
Food can be pasteurized either before or after being packaged into containers. Pasteurization of food in containers generally uses either steam or hot water. When food is packaged in glass, hot water is used to avoid cracking the glass from thermal shock. When plastic or metal packaging is used, the risk of thermal shock is low, so steam or hot water is used.Most liquid foods are pasteurized by using a continuous process that passes the food through a heating zone, a hold tube to keep it at the pasteurization temperature for the desired time, and a cooling zone, after which the product is filled into the package. Plate heat exchangers are often used for low-viscosity products such as animal milk, nut milk, and juices. A plate heat exchanger is composed of many thin vertical stainless steel plates that separate the liquid from the heating or cooling medium.
Shell and tube heat exchangers are often used for the pasteurization of foods that are non-Newtonian fluids, such as dairy products, ketchup, and baby foods. A tube heat exchanger is made up of concentric stainless-steel tubes. Food passes through the inner tube or tubes, while the heating/cooling medium is circulated through the outer tube.
Scraped-surface heat exchangers are a type of shell and tube that contain an inner rotating shaft having spring-loaded blades that serve to scrape away any highly viscous material that accumulates on the wall of the tube.
The benefits of using a heat exchanger to pasteurize foods before packaging, versus pasteurizing foods in containers are:
- Higher uniformity of treatment
- Greater flexibility with regard to the products that can be pasteurized
- Higher heat transfer-efficiency
- Greater throughput with many other processes of using the milk