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Pasteurization
By Anne Marie Helmenstine, Ph.D.
Pasteurization
(or pasteurisation) is the process by which heat is applied to food and
beverages to kill pathogens and extend shelf life.
Typically,
the heat is below the boiling point of water (100 °C or
212 °F).
While
pasteurization kills or inactivates many microorganisms, it is not a form of
sterilization, because bacterial spores are not destroyed.
Pasteurization
extends shelf life via heat inactivation of enzymes that spoil food.
Key Takeaways: Pasteurization
· Pasteurization
is the process of applying low heat to kill pathogens and inactivate spoilage
enzymes.
· It does
not kill bacterial spores, so pasteurization does not truly sterilize products.
· Pasteurization
is named for Louis Pasteur, who developed a method to kill microbes in 1864.
However, the process has been in use since at least 1117 AD.
Commonly Pasteurized Products
Pasteurization
may be applied to both packaged and unpackaged solids and liquids. Examples of
commonly pasteurized products include:
· Beer
· Canned
goods
· Dairy
products
· Eggs
· Fruit
juices
· Milk
· Nuts
· Syrup
· Vinegar
· Water
· Wine
History of Pasteurization
Pasteurization
is named in honor of French chemist Louis Pasteur.
In
1864, Pasteur developed a technique to heat wine to 50–60 °C
(122–140 °F) before aging it to kill microbes and reduce acidity.
However,
the technique had been in use since at least 1117 AD in China to preserve wine.
In
1768, Italian scientist Lazzaro Spallanzani demonstrated heating
meat broth to boiling and immediately sealing the container kept the broth from
spoiling.
In
1795, French chef Nicolas Appert sealed foods in glass jars and immersed them
in boiling water to preserve them (canning).
In
1810, Peter Durand applied a similar method to preserve foods in tin cans.
While
Pasteur applied his process to wine and beer, it wasn't until 1886 that Franz
von Soxhlet suggested pasteurization of milk.
So, why
is the process called "pasteurization," when it had been in use
before Pasteur?
The
most likely explanation is that Pasteur's experiments demonstrated particles in
the air, as opposed to pure air, caused food spoilage.
Pasteur's
research pointed toward microorganisms as the culprit for spoilage and disease,
ultimately leading to the Germ Theory of Disease.
How Pasteurization Works
The
basic premise behind pasteurization is that heat kills most pathogens and
inactivates some proteins, including enzymes responsible for food spoilage. The
exact process depends on the nature of the product.
For
example, liquids are pasteurized while flowing through a pipe. Along one
section, heat may be applied directly or using steam/hot water. Next, the
liquid is cooled. The temperature and duration of the phases are carefully
controlled.
Food
may be pasteurized after it has been packaged into a container.
For
glass containers, hot water is used to attain the desired temperature, to avoid
shattering the glass.
For
plastic and metal containers, either steam or hot water may be applied.
Improving Food Safety
Early
pasteurization of wine and beer was intended to improve flavor.
Canning
and present-day pasteurization of food primarily target food safety.
Pasteurization
kills yeast, mold, and most spoilage and pathogenic bacteria. The effect on food
safety has been dramatic, particularly
regarding milk.
Milk is
an excellent growth medium for numerous
pathogens, including those known to cause tuberculosis, diphtheria,
scarlet fever, brucellosis, Q-fever, and food poisoning from Salmonella, E. coli, and Listeria.
Prior
to pasteurization, raw milk caused many deaths. For example, approximately
65,000 people died between 1912 and 1937 in England and Wales from tuberculosis
contracted from consuming raw milk. After pasteurization, milk-related
illnesses dropped dramatically.
According
to the Centers for Disease Control, 79% of dairy-related disease outbreaks
between 1998 and 2011 were due to the consumption of raw milk or cheese.
How Pasteurization Affects Food
Pasteurization
greatly reduces the risk of food poisoning and extends shelf life by days or
weeks. However, it does affect the texture, flavor, and nutritional value of
foods.
For
example, pasteurization increases vitamin A concentration, decreases vitamin B2
concentration, and affects several other vitamins for which milk is not a major
nutritional source.
The color difference between
pasteurized and unpasteurized milk isn't actually caused by pasteurization, but
by the homogenization step prior to pasteurization.
Pasteurization
of fruit juice does not have a significant impact on color, but it does result
in the loss of some aroma compounds and the reduction of vitamin C and carotene
(a form of vitamin A).
Vegetable
pasteurization causes some tissue softening and nutrient changes. Some nutrient
levels are diminished, while others are increased.
Recent Advances
In the
modern era, pasteurization refers to any process used to disinfect food and
inactivate spoilage enzymes without significantly diminishing nutrient levels.
These
include non-thermal as well as thermal processes. Examples of newer commercial
pasteurization processes include high-pressure processing (HPP or
pascalization), microwave volumetric
heating (MVH), and pulsed electric field (PEF) pasteurization.
Anne Marie Helmenstine, Ph.D.
Chemistry Expert
Education
Ph.D., Biomedical Sciences, University of
Tennessee at Knoxville
B.A., Physics and Mathematics, Hastings
College
Introduction
Ph.D. in biomedical sciences from the
University of Tennessee at Knoxville - Oak Ridge National Laboratory.
Science educator with experience
teaching chemistry, biology, astronomy, and physics at the high school,
college, and graduate levels.
ThoughtCo and About Education chemistry
expert since 2001.
Widely-published graphic artist,
responsible for printable periodic tables and other illustrations used in
science.
Experience
Anne Helmenstine, Ph.D. has covered
chemistry for ThoughtCo and About Education since 2001, and other sciences
since 2013. She taught chemistry, biology, astronomy, and physics at the high
school, college, and graduate levels. She has worked as a research
scientist and also abstracting and indexing diverse scientific literature for
the Department of Energy.
In addition to her work as a science
writer, Dr. Helmenstine currently serves as a scientific consultant,
specializing in problems requiring an interdisciplinary
approach. Previously, she worked as a research scientist and college
professor.
Education
Dr. Helmenstine holds a Ph.D. in
biomedical sciences from the University of Tennessee at Knoxville and a
B.A. in physics and mathematics with a minor in chemistry from Hastings
College. In her doctoral work, Dr. Helmenstine developed ultra-sensitive
chemical detection and medical diagnostic tests.
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