Food preservation methods, like freezing, are widely used to maintain quality and extend shelf life. Freezing effectively slows spoilage caused by many microorganisms. However, questions often arise about the fate of viruses during this chilling process, particularly whether freezing eliminates these microscopic entities. Understanding freezing’s impact on viruses is important for food safety.
The Impact of Freezing on Viral Activity
Freezing does not destroy or eliminate viruses in food. Instead, it significantly reduces their activity by suspending metabolic processes. Viruses, unlike bacteria, require a host cell to replicate, so “killing” does not apply in the traditional sense. Low temperatures effectively put viruses into a dormant state, preventing replication or infection while food remains frozen.
Many foodborne viruses, such as norovirus and hepatitis A, remain viable even below -2°C. Their structural integrity generally remains intact during freezing, allowing for potential future activity. While some viral pathogens may experience inactivation at extreme freezing temperatures, this is not universal. For example, the lipid membrane of enveloped viruses like influenza can harden, contributing to their survival.
Viral Survival and Reactivation Post-Thawing
Viruses that survive freezing can reactivate once food thaws, provided conditions are favorable, such as finding a susceptible host cell. Thawing does not inactivate these viral particles. Outbreaks of norovirus and hepatitis A, for example, have been linked to contaminated frozen fruits, demonstrating retained infectivity after freezing and thawing.
Thawed viral particles remain structurally capable of causing infection. Freezing is an effective food preservation method, but it does not decontaminate food from viruses. Therefore, the same safety measures apply to thawed food as to food that has never been frozen.
Ensuring Food Safety: Beyond Freezing
Since freezing does not eliminate viruses, other measures are necessary for food safety. Cooking is an effective method for inactivating viruses, as heat denatures viral proteins. Cooking food to recommended internal temperatures, such as 165°F (74°C) for most meats, kills harmful germs. For liquid foods, simmering for a few minutes helps ensure safety.
Beyond cooking, hygiene practices prevent the spread of foodborne viruses. Thorough handwashing with soap and water, especially before preparing food, after handling raw ingredients, and after using the toilet, is essential. Preventing cross-contamination by keeping raw foods separate from cooked foods and using different cutting boards and utensils for each reduces risk. Individuals who are ill should avoid preparing food for others to prevent virus transmission.