Many people believe freezing food kills all harmful microorganisms, making it safe to eat once thawed. This misconception can lead to unsafe food handling. Pathogens are microorganisms that cause illness. Understanding what freezing does and does not do to these pathogens is essential for food safety.
How Freezing Affects Pathogens
Freezing primarily inhibits the growth and reproduction of most pathogens, putting them into a dormant state. The extremely low temperatures in a freezer, typically 0°F (-18°C) or below, significantly slow or halt the metabolic processes within these microorganisms. This prevents them from multiplying and causing spoilage while the food remains frozen.
While freezing stops growth, it does not destroy pathogens. Ice crystal formation within and around microbial cells can cause some physical damage, but this is rarely sufficient to kill most common foodborne pathogens. Once food thaws, surviving microorganisms can become active again, multiplying rapidly if conditions are favorable.
Pathogens That Survive Freezing
A range of common pathogens are known to survive freezing temperatures and can become active again upon thawing. Many types of bacteria, including Salmonella, Escherichia coli (E. coli), and Listeria monocytogenes, endure cold conditions. Listeria is particularly resilient, capable of growing even at refrigeration temperatures.
Viruses, such as Norovirus and Hepatitis A, also demonstrate resistance to freezing and can remain infectious in frozen foods. Certain parasites, like Toxoplasma gondii and Trichinella spiralis, can likewise survive freezing. Some bacteria can form protective spores or enter a dormant state, allowing them to persist through freezing and revive later.
Methods for Eliminating Pathogens
Since freezing does not reliably eliminate pathogens, other methods ensure food safety. Cooking food to its proper internal temperature effectively kills most foodborne bacteria, viruses, and parasites. A food thermometer always verifies that meats, poultry, and other perishable foods reach safe temperatures (145°F/63°C to 165°F/74°C, depending on food type).
Beyond heat, chemical sanitizers clean food preparation surfaces and utensils, reducing cross-contamination risk. Less common for home use, irradiation can also eliminate pathogens in commercial settings. Proper cooking remains the primary defense against microorganisms in food.
Ensuring Food Safety at Home
To prevent foodborne illness, follow the “4 Cs” food safety guidelines. First, “Clean” by washing hands, utensils, and surfaces often, especially after handling raw ingredients. Second, “Separate” raw meats, poultry, and seafood from ready-to-eat foods to prevent cross-contamination.
Third, “Cook” foods to their correct internal temperatures, using a food thermometer to confirm doneness. Finally, “Chill” perishable foods promptly by refrigerating them within two hours, or one hour if temperatures are above 90°F (32°C). Thaw frozen foods safely in the refrigerator, under cold running water, or in the microwave, never at room temperature. Always cook thawed foods thoroughly to eliminate surviving pathogens.