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At 4 a.m. in the Bohai Bay, crab farmers skillfully sort the mitten crabs hauled ashore. These fresh aquatic products then enter a 6-to-8-hour pre-cooling process, kicking off their freshness-preserving journey from the production area to the dining table.
By 5 or 6 a.m., the seafood markets are already bustling with people. Consumers may not know that the bag of fresh fish with ice shavings in their hands actually embodies the perfect combination of thousands of years of aquatic product preservation wisdom and modern cold chain technology.
Even today, with the highly developed modern refrigeration technology, ice storage preservation remains the earliest and most widely used method for the storage and transportation of aquatic products.
01 The Code of Ice Freshness: Ancient Techniques and Modern Technology
As the most traditional preservation technology, ice storage preservation is still widely used worldwide due to its unique advantages.
This method uses ice as a cooling medium. It lowers the temperature of aquatic products to near the ice melting point through ice or ice-water mixture, thereby effectively extending the freshness period of seafood.
Ice storage preservation is mainly divided into two types: dry ice method and wet ice method.
• The dry ice method involves crushing ice and sprinkling it on layers of fish to form a "layer of ice, a layer of fish", or mixing crushed ice with fish.
• The wet ice method first cools fresh water or seawater, then soaks the fish in the ice water for rapid cooling.
The choice of ice also requires careful consideration. Freshwater ice and seawater ice each have their own characteristics: the
melting point of seawater ice is lower than that of freshwater ice, at approximately -1°C, allowing it to absorb more heat.
Seawater fish are best preserved with seawater ice, as this maintains their inherent color and firmness, as well as the color of their
gills and the transparency of their eyes.
02 Ice Shape Evolution: From Block Ice to Flake Ice
Traditional block ice needs to be crushed before use, which is not only cumbersome to operate but also produces sharp-edged
crushed ice that easily damages aquatic products.
With technological progress, modern ice-making equipment such as flake ice machines, tube ice machines, and granular ice
machines have emerged, greatly improving the efficiency and quality of seafood preservation.
As an important cooling medium for modern seafood preservation, flake ice has the characteristics of being thin, dry, and loose, with a thickness of only 1.5-2.3 mm.
Flake ice has no sharp edges and will not pierce frozen objects. It can fill the gaps between cooled items, reduce heat exchange, and maintain the ice temperature.
In modern fisheries, seawater flake ice machines can even be directly installed on fishing boats. They use seawater to make ice,
enabling the freshly caught seafood to be quickly frozen and preserved.
03 Cold Chain Logistics: The Guardian of the "Ice and Snow Journey"
From the production area to the dining table, the "ice and snow journey" of seafood requires the support of a complete cold chain
logistics system. In the first half of this year, the total demand for China’s food cold chain logistics business reached 192 million tons, a year-on-year increase of 4.35%.
At the Shenzhen Airport International Cargo Terminal in Guangdong, an intelligent cold storage that can cover temperature control
needs from -25°C to 15°C ensures that imported iced fresh aquatic products "arrive at the port and go on the market on the same
day".
04 The Wisdom of Ice and Snow: Traditional Methods and Modern Innovation
Whether it is traditional ice storage preservation or modern cold chain logistics, temperature control has always been the core link.
During ice storage preservation, the container temperature needs to be controlled between -3°C and 1°C.
To ensure the quality of iced fresh products, the following measures are required:
1. Sort the fish promptly and quickly, classify them by species and size, and add ice and pack them as soon as possible.
2. Use sufficient ice, with fine ice particles. Sprinkle the ice evenly, ensuring a layer of ice between each layer of fish without any
gaps.
During transportation, meltwater management is also crucial. Plastic sheets can be used to separate each layer of fish boxes, and it
is necessary to ensure that meltwater can be drained from the containers and fish holds.
At the same time, pay attention to monitoring the temperature of the meltwater at all times; it should not exceed 3°C.