Time and temperature are two variables
that can affect the overall freedom from harmful levels of pathogens. The
disease-causing microorganisms found in food need to be present in
significant quantities in order to make someone ill after consuming it.
Once pathogens have established themselves in a food source, they will
either thrive or be destroyed, depending upon how time and temperature are
There are pathogens that can live at
all temperature ranges. For most of those capable of causing food borne
illness, however, the most friendly environment provides temperatures
within a range of 4 to 60oC (40 to 140oF). They are
usually destroyed at temperatures above 60oC. Storage at
temperatures below 4oC will destroy some pathogens; the cycle
of growth and reproduction will be slowed or interrupted in others.
When conditions are favorable,
pathogens can grow and reproduce at an astonishing rate. There are four
distinct stages of bacterial growth. The first is the lag phase, during
which newly introduced bacteria become adjusted to their environment.
During the accelerated growth phase, the bacteria reproduce rapidly.
Bacteria reproduce asexually; as each bacterium grows, it will split into
two bacteria of equal size. Under ideal circumstances, each bacterium can
reproduce every 20 minutes. One bacterium could produce 72 million
bacteria in just 12 hours.
The growth phase leads to the
stationary phase. This is a plateau, during which the rate of growth and
reproduction is matched by the rate of elimination. At this point, there
is no increase in the number of bacteria. Finally, there is the decline
phase. Now, the essential elements for life are exhausted. The elimination
rate exceeds the growth rate.
The time during which foods remain in
the danger zone is one of the most critical to the prevention of
contamination through food borne illness.