_by Edmund A. Zottola and Isabel D. Wolf_[1]
The telephone rings in a county Extension office. A harried voice says,
"My garden is growing more than my family can eat, what shall I do with
it? How can I keep it from spoiling?"
How many times during the gardening season is this scenario repeated in
an Extension office? Too often to count! The answers to these questions
are readily available in the many bulletins, folders, and leaflets on
food preservation available from county, State, and Federal Extension
agencies. The publications tell how to preserve food safely and
wholesomely, but do little else to explain why directions must be
followed precisely. Let's take a look at the whys.
To understand food preservation, first consider the sources. Home garden
food comes from plants: sources of raw food are living, biological
entities, continuing to metabolize after they are harvested. Plants also
provide a source of food for micro-organisms which can grow on or in
them, spoiling food before it can be eaten. The primary objective of
food preservation is to prevent food spoilage by preserving food until
it can be used by people.
Historically, food preservation and processing assured a food supply and
prevented starvation. This is probably the major reason why food is
processed today in many developing countries. In the United States,
however, affluence and a plentiful food supply now influence the reasons
for food preservation. Today, Americans live many miles from rural areas
where food is produced. Consequently, food must be preserved to assure
the nonfarm population an adequate supply.
Our people want a food supply that is safe, high in quality and
appearance, adequate nutritionally, and reasonably priced. Many
consumers try to obtain these food attributes by returning to the "old
ways" of growing and preserving food themselves.
To understand food preservation, let's look at five causes of food
spoilage or deterioration (four are biological, the fifth physical or
mechanical):
(1) The primary cause of food spoilage in the United States is
microbiological. Micro-organisms are small living organisms such as
yeast, molds, or bacteria. They are the chief causes of microbial
spoilage.
Related to microbiological spoilage of food and also a concern in food
preservation is microbiological food-borne disease. There are two types.
Salmonellosis is an example of a food infection where food may not
support growth of the micro-organisms but merely serves to transfer it
from the source to the human host. In the second type, the
micro-organism grows in the food and produces a poison or toxin which
when eaten, causes illness symptoms. Staphylococcal food poisoning is
the most common of the second type in the US.
Severity of the major types of food-borne disease in the United States
varies from the finality of botulism to the mild discomforts of
_Clostridium perfringens_ food poisoning. Food preservation techniques,
followed precisely, prevent food-borne disease.
(2) The second cause of food spoilage is vermin such as rodents, rats,
mice and insects that attack the food and eat or contaminate it before
humans can use it. These vermin ruin millions of pounds of food each
year.
[Illustration: WHAT ELSE CAN WE DO WITH TOMATOES?!!]
(3) Have you noticed how an apple, left at room temperature, eventually
gets soft, wrinkles, and dries out? This spoilage is called senescence:
an aging process caused by continued respiration of the apple,
eventually making it useless as food. Other foods also spoil this way.
(4) Related to senescence is chemical deterioration of food. The
development of rancid flavor in high fat-containing foods is a chemical
reaction which brings about an undesirable change. Loss of color or
bleaching and loss of vitamins, while food is stored, are chemical
deteriorations that can be controlled with proper preservation methods.
Both senescence and chemical deterioration are conveyed by organic
compounds called enzymes. These enzymes are produced by all living
organisms and their function is to speed up or cause the metabolic
reaction necessary for the organism's continued existence. The enzymes
will continue to act after the plant is harvested, and bring about
deterioration of the food unless controlled or destroyed. Preservation
methods have been developed to control or destroy these organic
catalysts.
(5) The last cause of food spoilage concerns food handling. Physical or
mechanical damage to the food causes bruising, crushing, cutting, and
wilting or water loss. These mechanical defects, besides detracting from
the food's appearance, allow easier entry of micro-organisms, insects,
and other vermin to cause spoilage and aging.
Food preservation processes have been developed to slow down, prevent,
or stop completely these processes of food spoilage.
An inherent part of food preservation is the package containing the food
before or after processing.
Packaging provides a convenient method of handling food, prevents
contamination during and after processing, bars vermin infestation,
supplies a container for storage, and is a necessary part of
preservation. An example would be a mason jar with proper seal for
pickling.
What are the major methods available for home preservation of food? How
are they carried out? Why do they prevent spoilage, food-borne disease,
and give desired attributes of safety, quality, appearance, nutrition,
and economy? The economics of food preservation will be developed in a
subsequent chapter. Let's explore the following available methods for
home preservation of food:
--Control of temperature of the food, heat or cool
--Control of the food's acid content
--Control of moisture content of the food
The major method used for home preservation of food is temperature
control. This includes canning with a pressure canner or a boiling water
bath, blanching food before freezing, refrigerating food, and freezing
it. Micro-organisms which cause disease and food spoilage are sensitive
to environment temperature variations. By increasing the food's
temperature, micro-organisms are destroyed. When the temperature is
decreased, their growth is inhibited.
Let's look at the temperature scale illustration and see how temperature
affects micro-organisms. To prevent growth of micro-organisms in food
and subsequent microbial spoilage, food must be kept out of the
temperature range that allows growth. This is most commonly achieved by
refrigerating or freezing. Refrigeration slows down or stops microbial
spoilage. Freezing stops it completely.
[Illustration: EFFECT OF TEMPERATURE ON MICRO-ORGANISMS]
Degrees
Fahrenheit
225 spore-forming bacteria killed
220-250 proper canning temperatures (low acid foods)
212 water boils; pressure canner needed to obtain
temperatures above boiling
170-210 non-spore-forming bacteria, yeasts, and molds killed
120-140 some bacteria can grow
98.6 body temperature
70-80 room temperatures may fall in this range
60-120 DANGER ZONE
most bacteria, including food-poisoning types, grow
rapidly over this temperature range
32 water freezes
30-60 cold-tolerant bacteria, yeasts and molds grow
0 no microbial growth
Enzymatic activity, while slowed down by freezing, is not stopped in
many vegetables and these enzymes must be destroyed by blanching the
vegetables before freezing to prevent enzymatic deterioration.
Successful preservation by freezing must deactivate any enzymes that
might be in the food as well as rapidly lower the food temperature to
below freezing to stop microbial activity.
Freezer burn, a common problem with frozen foods, comes from improper
packaging. Food moisture is lost in freezer burn, which results in
undesirable flavor and texture changes. Freezer burn can be controlled
by proper packaging, proper storing temperature, and avoiding long-term
storage.
Refrigeration or storage above freezing, but below room temperature,
preserves food for days and sometimes weeks. Refrigerated storage slows
down activities of enzymes in the food and reduces metabolism of the
contaminating micro-organisms.
Preservation of food by reduced temperature, refrigeration, or freezing
is achieved because enzyme activity and microbial deterioration are
slowed down or stopped.
Increasing the temperature of food to achieve preservation also results
in destruction of the micro-organisms that produce spoilage and disease.
Time and temperature regulate this preservation. Theoretically, since
food will be stored at temperatures which will allow most microbes to
grow, the ideal heat treatment needed to preserve the food would be one
that completely sterilizes the food, that is, kills all attendant
micro-organisms. To achieve complete sterilization, for example, every
particle of food in a jar must reach the required temperature and be
held there long enough to destroy all micro-organisms.