Small Ice Crystals—The Secret to Maintaining Flavor
Frozen food kept at temperatures below -18˚C can be preserved for years, as bacteria and mold cannot grow at such low temperatures. Freezing technology has enabled us to eat meat, fish and other foods imported from abroad, as well as ready-prepared frozen meals.
Rapid-frozen tuna from a ship arrives at port (Photo: JTB Photo Communications, Inc.)
However, there has been a downside to conventional freezing. Once food is frozen, it does not taste as good as freshly picked or freshly cooked food. The main reason is that when food is frozen, ice crystals inside the food expand, causing the cells to burst. When they burst, the nutrients turn to liquid (called "drip") and seep out as the food defrosts. The texture of the food also changes.
Tuna sushi—familiar to everyone now, thanks to progress in freezing technology (Photo: AFLO)
In an attempt to solve this problem, a method called "rapid freezing" was developed. When the water inside food freezes, ice crystals develop at temperatures between -1˚C and -5˚C. If this temperature range is passed through quickly (ideally within 30 minutes), most of the ice crystals do not grow too large, and the cells are not damaged. This process is the rapid freezing technique.
In Japan, rapid freezing technology was immediately put to use around 1960 on fishing boats to preserve tuna and other catches. The flavor of the rapid-frozen tuna also lasts much longer when preserved at a temperature below -50˚C. This has greatly helped to make Japanese dishes using raw fish—such as sashimi and sushi—popular around the world.