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Does Freezing Food Kill Bacteria? The Science Behind Food Safety

We often rely on freezing to preserve the quality and shelf life of our food, but does freezing food kill bacteria? In this article, we’ll explore the science behind food safety and discuss important factors that may impact the survival of harmful bacteria in frozen foods.

How Freezing Affects Bacteria

Freezing food affects bacteria in several ways. Low temperatures slow down bacterial growth and can put them into a dormant state, but they don’t necessarily kill all bacteria present.

Essentially, freezing can act as a “pause button” for bacteria, maintaining their number but preventing them from multiplying.

When the temperature is increased, such as when food is thawed, the bacteria may regain their ability to grow and multiply. However, the exact impact of freezing on bacteria varies depending on other factors, like the type of bacteria and the length of freezing, which will be explored further in the following sections.

Factors Affecting Bacteria Survival in Frozen Foods

While freezing can significantly slow bacterial growth, several factors influence their survival on frozen foods. These include the type of bacteria, length of freezing time, and freezing temperature. Ultimately, some bacteria may still be able to survive and proliferate once the food is thawed.

Bacterial Adaptation

Interestingly, some bacteria can adapt to cold environments, making them more resistant to the effects of freezing. These adaptable bacteria can even modify their cell structure and produce special proteins called ‘cold-shock proteins’ to withstand the harsh conditions.

As a result, it is crucial to follow proper food handling guidelines and not rely solely on freezing to ensure the safety of the food we consume.

Length of Freezing Time

The length of time food spends in the freezer is also an important factor in determining if bacteria will be killed or not. While freezing can significantly slow down the growth of bacteria, it doesn’t necessarily kill them all.

It is important to remember that once the food is thawed, any surviving bacteria can become active again and multiply, potentially reaching harmful levels. Therefore, it’s essential to handle frozen foods properly upon thawing, which includes proper cooking methods to kill off any remaining pathogens.

Type of Bacteria

It’s also crucial to consider the type of bacteria present in the food, as different strains exhibit different degrees of resistance to freezing. For instance, some bacteria can still thrive in frozen foods, although their activities are significantly slowed down.

Knowing the type of bacteria helps when deciding whether or not to freeze food and for how long to store it in the freezer to ensure maximum safety.

Temperature of Freezing

The temperature at which food is frozen plays a crucial role in determining the survival of bacteria. Warmer temperatures, like those in a frost-free refrigerator, will not be as effective at stopping bacterial growth as deep freezing at temperatures between -18 °C to -50 °C. It’s important to maintain consistent freezing temperatures to ensure food stays safe and bacteria-free.

Does Freezing Food Kill Bacteria

Some Bacteria that Can Survive Freezing

Although freezing can slow down bacterial growth, some bacteria can survive freezing temperatures. Examples of bacteria that can survive freezing include Listeria, Salmonella, and E. coli. These bacteria can still pose a potential health risk if not properly handled during food preparation and storage.


Listeria is particularly worrisome, as it can not only survive freezing temperatures but even continue to grow at a slow pace. This bacterium poses serious health risks, especially for pregnant women, newborns, the elderly, and those with weakened immune systems, making proper food handling crucial.


Salmonella is another dangerous bacteria that can withstand freezing conditions. Frozen food contaminated with Salmonella might still pose a risk, so it’s essential to follow safe food handling practices like proper cooking and maintaining cleanliness in the kitchen to ensure food safety.

E. coli

Similarly, E. coli is another bacteria that can endure freezing temperatures. This means that tainted foods may still pose a risk after being defrosted. To ensure safety, always practice proper food handling techniques, and cook to recommended temperatures to kill off any lurking bacteria.

Safe Food Handling Guidelines for Freezing

To ensure safety when freezing food, follow these guidelines: 

1) Cool food before freezing to discourage bacterial growth; 

2) Package food properly in airtight, moisture-resistant containers; 

3) Set your freezer to 0°F or lower; and 

4) Thaw food in a refrigerator, cold water, or via microwave.

Proper Packaging

Proper packaging is a crucial step in freezing food safely. Make sure to use freezer-safe bags or containers, and remove excess air to prevent freezer burn. This not only maintains the quality of your food, but also keeps bacteria at bay by preventing cross-contamination or moisture accumulation.

Defrosting Safely

When defrosting, avoid leaving food at room temperature or using hot water, as this can cause rapid bacterial growth. Instead, use the refrigerator, cold water, or the microwave’s defrost setting, which reduces the chance of bacteria multiplying on the food’s surface.


While freezing food can slow down bacterial growth, it doesn’t necessarily kill all harmful bacteria. To ensure food safety, it’s essential to follow proper food handling guidelines, including appropriate packaging and safe defrosting methods.