The freezer compartment of a household freezer typically operates at -18°C. However, in practice, due to factors such as how often the door is opened and closed, the temperature often only reaches around -12°C. While this is cold enough to freeze water, it does not freeze the core of the food, so it may appear frozen at first glance. Proteins, enzymes, and lipids remain unfrozen, causing the taste and texture of the food to deteriorate significantly within a few weeks.
On the other hand, ultra-low temperature freezing can freeze all the components of fish meat, suppressing protein decomposition and stopping lipid oxidation. This makes it possible to store food for up to six months. All living organisms begin to age and deteriorate after death, eventually leading to oxidation and decay. The temperature that can stop this process is the world of ultra-low temperature freezing at -42°C.
Inhibition of enzymatic protein degradation
Under normal conditions, proteins that have ceased activity at room temperature undergo enzymatic degradation. For example, the proteins in freshly caught fish are in a high-molecular-weight state. Through enzymatic degradation, they break down into lower-molecular-weight compounds, advancing the aging process. If this process progresses too far, decay occurs.
Additionally, fish have a high water content of 70%, making them age much faster than livestock meat. Therefore, the key is to quickly cool the fish to ultra-low temperatures after catching them and then thaw them while maintaining the aging process.
Inhibition of fat oxidation
What is commonly referred to as “freezer burn” occurs when the fat naturally present in food rises to the surface and oxidizes, causing the color to turn yellowish and the appearance and taste to deteriorate. To prevent this, it is essential to prevent the food from coming into contact with air. Furthermore, by storing it in an ultra-low temperature environment, the oxidation process itself can be almost completely halted.
Inhibition of microbial proliferation
Even at the -18°C environment of a household freezer, microbial proliferation can be largely suppressed. However, for complete inhibition of all types of microbial growth, ultra-low temperatures are ideal.
Real-world applications
Ultra-low temperature freezing is already widely used in the seafood industry. At Tokyo’s Toyosu Market, premium tuna is stored and transported at -60°C to preserve its deep red color, fatty texture, and fresh taste for overseas shipments. In Hokkaido, Pacific saury is frozen at -50°C immediately after being caught on specialized vessels, allowing them to be enjoyed months later with near-fresh quality. Some Japanese supermarket chains use -45°C freezing for salmon fillets, enabling them to offer sashimi-grade products all year round while minimizing quality loss.
In sushi restaurants, anago (saltwater eel) is often purchased in bulk when prices are stable, stored at ultra-low temperatures, and thawed to maintain quality and cost efficiency. Likewise, ikura (salmon roe) is typically prepared in autumn, its peak season, and frozen for year-round use, ensuring consistent flavor and texture regardless of the season.
The fact that a 10,000-year-old mammoth excavated from Siberian permafrost was still edible after being cooked is a testament to the capabilities of ultra-low temperatures.