Danger zone

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The "danger zone" is the temperature range allowing multiplication of pathogenic bacteria ("germs"). Consuming food held too long in this temperature range increases the risk of food poisoning. The danger zone is given by the US FDA as 4.4°C/40°F to 60°C/140°F, though modern research indicates that this is a flawed approach:
 * The concept of the "danger zone" is based on an oversimplification of microbial growth patterns. Not all temperatures within the danger zone are equally dangerous. Most pathogens grow slowly at temperatures below 10°C/50°F. Their growth accelerates modestly with increasing temperature and is typically fastest near human body temperature, 37°C/98.6°F. Beyond this optimum, higher temperatures sharply curtail the growth of most pathogens until they stop growing completely and start to die.

Danger zone research
According to O. Peter Snyder Yersinia enterocolitica and Listeria monocytogenes are capable of multiplication at -1.5°C/29.3°F, setting the lower limit of the danger zone, and Clostridium perfringens which can multiply from 15°C/59°F to 52.3°C/127.5°F sets the upper limit of the danger zone. As home refrigerators usually do not cool below 4.4°C/40°F, this is taken as the lower limit of the danger zone for practical purposes; but at 4.4°C/40°F Listeria monocytogenes and Yersinia enterocolitica can multiply about 1 time every day. A 5 generation multiplication (32x) of a normal level of food contamination is considered as a minimal threat, thus a 5 day storage at 4.4°C/40°F is considered safe.

Clostridium perfringens is the fastest multiplying pathogen and dictates heating time from 4.4°C/40°F to 54.4°C/130° to be less than six hours.