3. Food Preservation
the process of treating and handling food in
such a way as to stop or greatly slow down
spoilage and prevent foodborne illness while
maintaining nutritional value, texture and
flavor .
4. Methods
food preservation is one of the oldest technologies used by human beings. In this,
we'll look at all of the different preservation techniques commonly used today,
including:
Refrigeration and freezing
Canning
Irradiation
Dehydration
Freeze-drying
Salting and Pickling
Pasteurizing
Fermentation
Cheese-making
5. NOTE In certain cases, a preservation technique may also destroy
enzymes naturally found in a food that cause it to spoil or
discolor quickly. An enzyme is a special protein that acts as a
catalyst for a chemical reaction, and enzymes are fairly fragile.
By increasing the temperature of food to about 150 degrees
Fahrenheit (66 degrees Celsius), enzymes are destroyed . A food
that is sterile contains no bacteria. Unless sterilized and sealed,
all food contains bacteria. For example, bacteria naturally living
in milk will spoil the milk in two or three hours if the milk is left
out on the kitchen counter at room temperature. By putting the
milk in the refrigerator you don't eliminate the bacteria already
there, but you do slow down the bacteria enough that the milk
will stay fresh for a week or two.
Let's look at all of the different forms of food preservation in
detail.
6. 1. REFRIGERATION AND FREEZING
Refrigeration and freezing are probably the most popular
forms of food preservation in use today. In the case of
refrigeration, the idea is to slow bacterial action to a
crawl so that it takes food much longer (perhaps a week
or two, rather than half a day) to spoil. In the case of
freezing, the idea is to stop bacterial action altogether.
Frozen bacteria are completely inactive.
Refrigeration and freezing are used on almost all foods:
meats, fruits, vegetables, beverages, etc. In general,
refrigeration has no effect on a food's taste or texture.
Freezing has no effect on the taste or texture of most
meats, has minimal effects on vegetables, but often
completely changes fruits (which become mushy).
7. 2. Caning
Since 1825 or so, canning has provided
a way for people to store foods for
extremely long periods of time. In
canning, you boil the food in the can to
kill all the bacteria and seal the can
(either before or while the food is
boiling) to prevent any new bacteria
from getting in. Since the food in the
can is completely sterile, it does not
spoil.
Once you open the can, bacteria
enter and begin attacking the food,
so you have to "refrigerate the
contents after opening" (you see that
label on all sorts of food products --
it means that the contents are sterile
until you open the container).
8. 3. Dehydration
many foods are dehydrated to preserve
them. If you walk through any grocery
store you may notice the following
dehydrated products:
Powdered milk
Dehydrated potatoes in a box
Dried fruits and vegetables
Dried meats (like beef jerky)
Powdered soups and sauces
Pasta
Instant rice
9. .
Normally, drying completely alters
the taste and texture of the food, but
in many cases a completely new
food is created that people like just
as much as the original!
10. 4. Freeze-drying
Freeze-drying is a
special forms of drying
that removes all
moisture and tends to
have less of an effect on
a food taste than
normal dehydration
does .
01
In freeze-drying, food is
frozen and placed in a
strong vacuum. The
water in the food then
sublimates that is, it turns
straight form ice into
vapors.
02
Freeze-drying is most
commonly used to
make instant coffee, but
also works extremely
well on fruits such as
apples.
03
11. 5. Salting
Salting, especially of meat, is an ancient
preservation technique. The salt draws out
moisture and creates an environment
inhospitable to bacteria. If salted in cold
weather ( so that the meat does not spoil
while the salt has time to take effect), salted
meat can last for years.
Today, salting is still used to create salt-cured
“country ham’’ found widely in the southern
united states, dried beef and corned beef and
pastrami, which are made by soaking beef in
a 10-percent salt water brine for several
weeks.
12. 6. Pickling
Pickling was widely used
to preserve meats, fruits
and vegetables in past,
but today is used almost
exclusively to produce
“pickles’’ or pickled
cucumbers.
Pickling uses the
preservative qualities of
salts combined with the
preservative qualities of
acid , such as acetic acid
(vinegar) .
13. 7. Pasteurizing
Pasteurizing is a compromise. If you
boil the milk you can kill all bacteria
and make the food sterile, but you
often significantly affect the taste
and nutritional value of food.
Ultra high temperature (UHT)
pasteurization completely sterilizes
the product. It is used to created
"boxes of milk" that you see on the
shelf at the grocery store. In UHT
pasteurization, the temperature of
the milk is raised to about 285
degrees F (141 degrees C) for one or
two seconds, sterilizing the milk.
14. 9. Fermentation
Fermentation uses yeast (see How Bread
Works for more information on yeast) to
produce alcohol. Alcohol is a good
preservative because it kills bacteria.
When you ferment grape juice you create
wine, which will last quite a long time
(decades if necessary) without
refrigeration. Normal grape juice would
mold in days.
15. 10. Cheese making
Cheese is way of preserving milk for long periods of time. In the process, the milk in
cheese becomes something completely unlike milk, but cheese has its own interesting
and delicious properties. Cheese-making is a long and involved process that makes use
of bacteria, enzymes and naturally formed acids to solidify milk proteins and fat and
preserve them. Once turned into cheese, milk can be stored for months or years.
