1. Are Bacteria in the Freezer Dead or Just Sleeping?
Inside a freezer, mold does not grow on food, and odors do not develop. This makes it tempting to think the germs have died. According to the FSIS, freezing at about minus 18°C (0°F) stops bacteria, yeast, and mold from being active. However, this is not sterilization. When thawed and the temperature rises, they can start moving again, multiply, and reach levels that cause illness [1].
Japanese guidelines agree with this view. The Sapporo City food poisoning alert warns that thawing frozen meat or fish at room temperature can allow attached food-poisoning bacteria to increase. If there are many bacteria, heating might not reduce them enough [4].
The bacteria in the freezer are like animals in hibernation; they have just stopped moving. However, this is only an analogy for the stopping of movement; the bacteria are not sleeping and dreaming. As the temperature rises during thawing, the paused bacteria can begin to multiply again. The longer the outside stays at a dangerous temperature, the more opportunity there is for this to happen.
When the temperature rises during thawing, paused bacteria can start multiplying again. The longer the outer parts stay at a risky temperature, the greater the chance that bacteria will increase.
2. Why Is Thawing Food on the Kitchen Counter Dangerous?
Imagine taking rock-hard meat out onto the kitchen counter to thaw. The surface becomes soft and reaches room temperature, but the center may still be frozen. The FSIS states that you should not thaw food on the kitchen counter. The reason is that while the outside enters the "danger zone," the center might still be frozen [2]. The danger zone is defined by the FSIS as 40 to 140°F (about 4 to 60°C). Note that numbers vary by source; for example, the US FDA Food Code lists it as 41 to 135°F [2].
This means thawing is not "warming everything at once." The outside stays in the danger zone for a long time, while the center remains frozen. The longer the outside stays in the danger zone, the more room there is for bacteria on the outside to grow.
The FSIS lists safe methods as using the refrigerator, cold water, or a microwave [2]. Hiroshima City also calls for using refrigerators or microwaves and advises against thawing at room temperature [3].
Do not thaw food on the counter. The outside can reach the danger zone (40–140°F, about 4–60°C) while the center is still frozen. Safe methods include the refrigerator, cold water, or a microwave.
3. What Happens to the Water in Food When It Freezes?
Water increases in volume when it turns to ice. This is the same as when you freeze a glass of water and the surface bulges upward. Food contains a lot of water. Appliance explanation articles state that moisture, which has increased in volume due to freezing, breaks cells as it freezes. When thawed, water flows out from these broken cells, causing a loss of flavor [5]. A professional journal article (MDPI Foods) also notes that ice crystals damage tissue [6]. This leaked water is called "drip."
A Japanese research report using X-ray CT to examine beef suggests that quality decline after thawing is caused by ice crystals melting and leaving as moisture (drip) containing nutrients. On the other hand, it notes that cavities left by the ice are crushed by surrounding tissue and do not remain [8].
This research states that this is "presumed," so we cannot say the mechanism of how ice breaks cells is fully understood in detail. Still, it is a solid clue that the state of water in food changes between freezing and thawing.
4. How Do Freezing Speed and Thawing Speed Affect Food?
It is said that the speed of freezing also affects the result. A 2023 article in MDPI Foods and a 2021 review in Springer state that slow freezing creates large, irregular ice crystals. These damage tissue during thawing, leading to increased drip and reduced softness [6]. An article from Kaden Watch also states that the faster you freeze, the less loss of taste and texture there is [5]. These points were confirmed in summaries.
There is also Japanese research on thawing speed. When comparing fish meat samples thawed slowly in air versus rapidly in water, the slow-thawed samples had more damaged muscle cells, more drip, and lower enzyme activity (Ca-ATPase activity) [7].
This is a result for fish meat and cannot be directly applied to other meats or vegetables. It does not mean "slow thawing in the fridge is bad." Refrigerator thawing is recommended because it avoids the temperature range where bacteria multiply easily.
You might wonder if the nutrients dissolved in the drip serve as food for bacteria. However, there is no direct source linking this specifically to spoilage here. The main reason for spoilage is that bacteria start moving again during thawing.
5. Try It at Home: Watch Water Expand When It Freezes
You can observe how water expands when it freezes. Put water in a cup or container and place a sticker at the water level. Freeze it and see if the ice surface bulges above the sticker. Use an open container and be careful not to spill.
To see drip, place frozen strawberries or broccoli on a plate and thaw them in the refrigerator. Observe the water that collects on the plate. The amount varies by food, so compare only the same type of food if you want to measure it. If testing with raw meat or fish, wash your hands carefully and do it with an adult.
Read the instructions on store-bought frozen food packages. Look at what thawing or cooking methods are written there. Compare how these differ by food type.
If you read Japanese sources, the pages from Hiroshima City [3] and the Sapporo alert [4] are available in Japanese. They describe thawing methods and the dangers of leaving food at room temperature.
If using raw meat or fish, pay attention to hygiene and do it with an adult.