Clostridium perfringens is a bacterium commonly found in the environment, including soil, dust, and the intestines of animals and humans. As a cause of foodborne illness, it is particularly associated with foods that have been cooked in large quantities, such as meat, poultry, and gravies, that are subsequently held at improper temperatures.
The bacteria create protective spores that survive normal cooking temperatures. When cooked food cools slowly, these spores germinate and the bacteria multiply rapidly. The illness is caused by an enterotoxin that the bacteria release as they grow inside the food or once ingested. Preventing this food poisoning relies entirely on ensuring cooked food moves quickly out of the range where the bacteria thrive, as rapid multiplication results from failures in proper time and temperature control.
Managing the Temperature Danger Zone
Preventing C. perfringens growth requires controlling food temperature and avoiding the “Temperature Danger Zone” (TDZ). This zone, where the bacteria multiply most rapidly, is defined as 40°F and 140°F (4°C and 60°C). Foods should not remain within this range for more than two hours total.
The initial cooking process kills the active vegetative cells of the bacteria, but the heat-resistant spores remain. To ensure the destruction of active cells, foods like beef roasts and whole poultry must be cooked to their safe minimum internal temperatures. Once cooked, the food must either be kept hot or immediately cooled.
For food intended for immediate service or hot holding, it must be maintained at a temperature of 140°F (60°C) or warmer. Holding food below this temperature creates an environment where the bacteria can proliferate to dangerous levels. The practice of keeping food warm in a slow cooker or on a buffet line set below this threshold is a common contributing factor to outbreaks.
Essential Rapid Cooling Techniques
Improper or slow cooling of large volumes of cooked food is the most frequent cause of C. perfringens food poisoning outbreaks. Once cooking is complete, the goal is to move the food through the TDZ as rapidly as possible. The established guideline requires a two-stage cooling process.
The first stage mandates that food must cool from 140°F to 70°F (60°C to 21°C) within a maximum of two hours. The second stage requires the temperature to drop from 70°F to 40°F (21°C to 4°C) or below within an additional four hours. This combined six-hour window ensures the food spends minimal time in the ideal growth range for the bacteria.
To facilitate this speed, large quantities of food must be actively managed. A primary technique involves dividing large items, such as roasts or large pots of soup, into smaller portions. These portions should be placed into shallow containers, ideally less than two inches deep, to maximize the surface area exposed to cold air.
Another effective method is using an ice bath, where the containers of hot food are submerged in a sink or large container filled with ice and a small amount of water. Stirring the food frequently helps to distribute the cold more quickly throughout the entire mass. Specialized equipment, like cooling wands or blast chillers, can also be employed to speed up the process, especially when dealing with commercial-sized batches.
Safe Reheating and Serving Guidelines
The final preventative step is ensuring proper reheating and safe serving practices. Leftovers that have been safely cooled and stored must be reheated to an internal temperature of at least 165°F (74°C). This temperature must be reached rapidly and held for at least 15 seconds to destroy any surviving bacteria.
Use a food thermometer to verify the core temperature, especially in the thickest part. Reheating should be done using a stovetop, oven, or microwave, which achieve the target temperature quickly. Slow-heating devices, such as slow cookers or chafing dishes, should not be used for reheating, as they spend too much time in the TDZ.
Only reheat the amount of food that will be consumed immediately. Once food has been reheated to 165°F, it must be kept at 140°F or above if it is to be held for serving. Any perishable leftovers that have been held in the Temperature Danger Zone for more than two hours after serving should be discarded to eliminate the risk of illness.