1. Why Cold Temperatures Stop Microbes From Spoiling Food
Food spoils because tiny living things called microbes grow rapidly inside it. These tiny creatures prefer warm places. When the temperature drops, the chemical reactions inside their bodies slow down, and their growth speed slows down too. If you cool food to below -18°C (0°F), most microbes stop moving and enter a state like sleep.
2. Why Freezing the Water in Food Helps Preserve It
Microbes need water to grow. However, when the water inside food freezes and turns into ice, the microbes can no longer use that water. Cooling food and freezing its water are two different effects. Because these two effects happen at the same time, food becomes even harder to spoil.
3. How Ice Crystals Change the Taste and Texture of Frozen Food
When water freezes, its volume (size) increases by about 10%. If food freezes slowly, large ice crystals form. These big crystals physically damage the cells, which are the tiny rooms that make up the food’s body. On the other hand, if you freeze food quickly in a short time, the ice crystals stay small. This means the cells are less likely to be damaged, and the taste and texture are better preserved when the food thaws [2]. The water that comes out when you thaw frozen food, known as drip, leaks out from these damaged cells.
4. How Clarence Birdseye Discovered Quick Freezing
In 1912, an American named Clarence Birdseye was working in the fur trade in the Labrador region of northern Canada. In 1914, he noticed that the local people froze fish they had caught in outside air that was about -40°C (-40°F). Even when they thawed and ate the fish months later, it kept a taste and texture like it was freshly caught [3]. The reason was that the fish froze very quickly in the extremely cold environment. Birdseye thought about recreating this "freezing quickly" mechanism with a machine. He founded a company in 1925 to develop a quick-freezing machine. In 1930, frozen foods using his technology were sold to the general public for the first time [3].
5. Why Frozen Food Is Kept at -18°C
Keeping frozen food at -18°C (0°F) or below is an international standard [5]. Even if food is frozen into small crystals at first, if the temperature goes up and down repeatedly during storage, the small ice crystals stick together and slowly grow larger. This process is called recrystallization. By storing food at as low a temperature as possible and avoiding temperature changes, this growth is prevented [2].
6. Whether Freezing Kills All Microbes in Food
Freezing can stop the activity of microbes, but it does not kill all of them. Because of this, it is recommended to eat food soon after thawing it. Refreezing food that has already been thawed is not recommended for reasons of taste and safety [6].
7. How to Check Your Home Freezer's Temperature
If you want to investigate further, try checking the temperature of your home freezer with an adult. Today, you can check if your freezer is set to -18°C (0°F) or below. You can also compare the texture of frozen vegetables with raw vegetables to observe the difference. If you write down just one word that interests you, it can be a starting point for looking things up later. For example, asking "Does water activity relate to other foods?" is enough to start.