Freezing Techniques for Frozen Seafood Products – Knowledge essential for engaging in the seafood industry

frozen seafood product from haidongseafood

In the seafood freezing industry, we adopt various processing methods to maintain the freshness and nutritional value of seafood for long-term preservation and long-distance transportation.  Firstly, we have three main processing methods to maintain the freshness of seafood: Live Seafood, Seafood in Iced Fresh, and frozen seafood. According to the different processing locations, there are two types of freezing: ship freezing and shore freezing. Each method is designed for specific types of seafood and preservation needs. Understanding these different seafood processing and freezing methods is crucial to ensuring that the seafood products we consume are both fresh and nutritious. This knowledge not only helps industry professionals improve work efficiency but also makes consumers more confident in enjoying delicious seafood dishes.

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Live Fresh seafood

as the name indicates, refers to seafood that is still alive. Many people believe that fresh seafood is the best because it is the most fresh. If you are near a fishing spot, it is reasonable to request fresh food. However, if you are located inland or want to eat imported seafood, it is difficult to guarantee the survival rate and fullness of the meat.

Taking the example of the resilient crayfish, they usually last about a week during transportation, which is why they can usually be eaten fresh. However, during transportation, lobsters lack food and water, resulting in shriveled and thin meat. This is also why after cooking live lobsters, the meat often separates from the shell, and even the meat in the claws is only one-third.

In the past, the most famous restaurants would fatten crabs that had lost meat and fat after transportation to achieve the best taste before serving customers. However, we currently do not have the means to do so, so it is best to eat fresh seafood in coastal areas. Otherwise, even if transportation can ensure the survival of seafood, the actual taste will be greatly inferior to seafood processed in other ways.

sea food iced fresh

Seafood in Iced Fresh

Seafood that is covered with layers of crushed ice for preservation in a short period after being brought ashore is known as “iced fresh.” The use of crushed ice can reduce the temperature of seafood to approximately 0℃ and keep it within this temperature range during transportation and storage. Within this temperature range, the flavors of seafood or meat do not freeze and can be maintained for a short period of time. To put it simply, seafood that is not frozen on ice in supermarkets is considered to be “iced fresh” and not frozen. This method of processing seafood has a shorter shelf life and is not suitable for long-distance transportation.

frozen seafood

Frozen seafood

Frozen seafood is seafood that has been rapidly frozen and stored at temperatures below -18 ℃. The primary technology used in export factories is IQF (Individual Quick Freezing), which maximizes the preservation of product freshness. The rapid freezing process ensures that the central temperature quickly reaches -18 ℃, fully freezing the seafood and preventing quality changes caused by fluidity. This process also locks in the nutrients and moisture of the seafood, preventing loss, and effectively killing bacteria to maintain the original quality of the product and allow for long-term storage. Overall, frozen seafood ensures the nutrition and quality of the product.

In the field of frozen seafood processing, we divide frozen seafood into two categories based on the quality of the meat and the characteristics of the seafood: raw frozen and cooked frozen. Each method has its advantages, suitable for different types of seafood.

Raw Frozen Seafood: As the name suggests, raw frozen refers to seafood that is frozen directly at low temperatures without being cooked beforehand. This method’s advantage lies in the variety of cooking options it offers, providing consumers with more culinary possibilities. However, the weight at the time of purchase often includes moisture, and the cooking time tends to be longer.

Cooked Frozen Seafood: Cooked frozen seafood is boiled in salt water before undergoing rapid ultra-low temperature freezing. This process is carried out when the seafood is at its freshest and most plump, effectively maintaining its fresh and tender meat quality. The advantages of cooked frozen seafood include easy preservation, commonality, the ability to be imported whole, maintaining an intact appearance, tender meat quality, and a shorter cooking time.

Blanched Frozen Seafood: Blanching involves briefly boiling the caught seafood (mostly crustaceans) in seawater to achieve a semi-cooked state, followed by rapid freezing at low temperatures. Commonly blanched and frozen seafood includes lobsters, mussels, jade snails, etc.

Some types of seafood are not suitable for raw freezing and must undergo cooked freezing to maintain the best taste. For example, shelled seafood such as shrimp, crabs, lobsters, and certain shellfish are primarily processed by cooking and freezing. This is because raw freezing can cause an imbalance inside and outside the cell wall, leading to meat shrinkage and affecting the taste.

It’s worth noting that many of the sashimi dishes we eat daily are actually cooked and frozen, rather than raw. Less professional Japanese restaurants may not be aware of this fact. There are two methods of cooked freezing: fully cooked and partially cooked. Fully-cooked seafood is commonly found in various types of shrimp and crab, while semi-cooked seafood includes items like Arctic shellfish.

Understanding these different frozen processing methods is crucial for those in the frozen seafood business. This knowledge not only helps in providing higher-quality products to consumers but also offers seafood enthusiasts more cooking choices and gastronomic experiences.

Ship freezing vs Shore freezing

Ship freezing refers to the process of directly processing seafood on board after fishing, including cleaning, removing dirt, blanching, packaging, and freezing, to ensure the quality of seafood to the greatest extent. After thawing, it can present a fresh taste and sufficient nutrition, and the freshness is even better than that of live seafood transported over long distances. Modern ocean fishing generally uses the method of “ship freezing”. For example, the fishing of wild Argentine red shrimp uses this freezing method. So, imported Argentine red shrimp is very popular in our country. In this way, you can both eat wild game and supplement your nutrition.

Shore freezing, on the other hand, is a freezing method opposite to “ship freezing”. As the name suggests, after seafood is caught, ice is added to the ship to keep the seafood at a low temperature. That is, the fishing ship arrives at the processing factory after docking, and then begins processing the seafood. This freezing method, if caught in the open sea, cannot guarantee that the seafood is fresh, and it is normal for death on the return journey; If caught near the sea, the mortality rate of seafood will be lower. After the seafood is ashore, large fishing companies will sort it and then freeze it. Of course, the quality of shore-frozen seafood cannot be compared to ship-frozen seafood. Freezing on the shore is better for preservation than freezing on the ship.

How to achieve reasonable thawing for frozen seafood?

When frozen seafood is thawed, it is important to ensure that the temperature rises within a certain range (from 0 ° C to 6 ° C) in order to restore the absorption of the melted water from the ice crystals inside the food into the seafood cells. Rapid melting can lead to the loss of this water, turning it into juice that flows out. Since these juices contain water-soluble nutrients such as protein, minerals, and vitamins, the nutritional value of seafood can be compromised. Therefore, achieving reasonable thawing of frozen seafood is crucial for maintaining its quality.

In general, a shorter thawing time is better, and the closer the color of the seafood is to its original color, the better. Thawing methods include using natural air at around 1-5 degrees Celsius, spraying with tap water at around 15 degrees Celsius, or using flowing water at around 10 degrees Celsius. However, seafood should not be soaked in static water, and it should not be thawed in warm water.

Imported frozen seafood is usually pre-processed immediately after being caught on board, then rapidly frozen and stored in a -25 degree cold storage on board. Thawing can be done by spraying cold water, but experienced chefs often use a better method known as “low-temperature thawing,” which helps preserve the taste and nutrition of the thawed seafood.

Low-temperature thawing ensures that the soluble components of seafood are not lost, allowing nutrients to remain in the meat while preserving freshness. The temperature of the refrigerated warehouse is usually controlled at around 4.4 ℃, which is an appropriate temperature for reducing foodborne diseases. The low-temperature thawing environment also slows down bacterial activity, resulting in fresher and safer thawed products.

How do supermarkets achieve low-temperature thawing?

After removing frozen seafood from the freezer, it is placed in a refrigerator (0-3 ℃) for thawing, which usually takes 24-36 hours. It is recommended to remove the frozen product one day in advance and thaw it the next morning, depending on the size of the ingredients.

During thawing, the frozen product should be placed in a drainable container to prevent melted water from gathering and soaking the ingredients, thereby affecting the quality. The refrigerated warehouse used for thawing should not be overcrowded, as cold air needs sufficient circulation space to ensure food safety.

How to determine the degree of thawing?

Customers should be informed that if they want to make sashimi for consumption, such as Argentine red shrimp, Mozambique peach red shrimp, Spanish crimson tribute shrimp, etc., or if they want to consume a cooked frozen product immediately after thawing, such as Chilean king crab, Arctic sweet shrimp, etc., it is recommended to thaw the seafood to a degree of 8 for the best taste. On the other hand, if the seafood is to be cooked and consumed after thawing, it needs to be completely thawed to shorten the cooking time, ensure even heating, and enjoy a more delicious taste. Once frozen seafood is thawed, it should be cooked immediately to avoid spoilage and loss of nutrients due to the recovery of microbial and enzyme activity.


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