Food Preservation - Spoilage Factors
All foods exposed to air at room temperature will spoil slowly unless preserved in some way.
Why food spoils
Food spoilage is the result of enzyme action and growth of microorganisms.
Enzymes
Enzymes are proteins found in all plants and animals. If uncooked foods are not used while
fresh, enzymes cause undesirable changes in colour, texture and flavour. Enzymes are destroyed easily
by heat processing.
Microorganisms
There are three types of microorganisms that cause food spoilage -- yeasts, molds and bacteria.
- Yeasts growth causes fermentation which is the result of yeast metabolism. There
are two types of yeasts true yeast and false
yeast. True yeast metabolizes sugar
producing alcohol and carbon dioxide gas. This is known as fermentation.
False yeast grows as a dry film on a food surface, such as on pickle brine. False yeast occurs in foods
that have a high sugar or high acid environment.
- Molds grow in filaments forming a tough mass which is visible as `mold growth'.
Molds form spores which, when dry, float through the air to find suitable
conditions where they can start the growth cycle again.
- Both yeasts and molds can thrive in high acid foods like fruit, tomatoes, jams, jellies
and pickles. Both are easily destroyed by heat. Processing high acid foods at a
temperature of 100°C (212°F) in a boiling water canner for the appropriate length of time
destroys yeasts and molds.
- Bacteria are round, rod or spiral shaped microorganisms. Bacteria may grow under
a wide variety of conditions. There are many types of bacteria that cause spoilage.
They can be divided into: spore-forming and
nonspore-forming. Bacteria generally prefer
low acid foods like vegetables and meat. In order to destroy bacteria spores in a
relatively short period of time, low acid foods must be processed
for the appropriate length of time at 116°C (240°F) in a pressure canner. (Temperatures higher than 100°C [212°F] can
be obtained only by pressure canning.)
Clostridium botulinum is the
spore-forming bacteria that is the cause of concern when home
canning low acid foods. While the bacteria is destroyed at 100°C, it has the ability to form hardy spores
that can survive boiling water processing. These spores can germinate and grow in a low acid
environment in the absence of air. As they grow they give off a deadly toxin.
Clostridium botulinum spores can be destroyed by heat processing at a temperature of
116°C. Foods that are low in acid such as meat,
poultry, seafood or vegetables must be processed in a pressure canner in order to obtain temperatures
of 116°C.
Clostridium botulinum is not a spoilage concern in high acid foods. The spores cannot grow or
produce the deadly toxin in high acid foods. High acid foods can be safely heat processed in a boiling
water canner.