Processing Technology in Surimi Production: Steps and Methods

Surimi is one of the most technically refined seafood ingredients in modern food processing. Derived from the Japanese word meaning “ground meat,” it is the concentrated myofibrillar protein base used to produce imitation crab sticks, fish balls, kamaboko, and a wide range of structured seafood products. Surimi processing technology involves washing minced fish to purify and concentrate muscle proteins, which are then either further processed into secondary products or stabilized with cryoprotectants and frozen for storage. What makes surimi production unique is the precision required at each stage – from how the fish is cleaned to how the final mince is dewatered. Each step directly determines the protein quality, gel strength, and shelf life of the final product.

Starting point: fish cleaning and initial preparation 🔗

The surimi production line begins long before any machine touches the fish. Surimi processing generally involves sorting, heading, gutting, deboning, washing, dewatering, and mixing with cryoprotectants – and the quality of each downstream step depends heavily on how well the fish is handled at the start.

Fresh fish arriving at the processing facility are sorted by size and species. Fish are categorized by size and undergo a thorough cleaning process that includes the removal of heads, viscera, skin, and bones. Temperature management is critical from the very beginning. Processing at low temperatures (ideally below 10°C) prevents bacterial growth and slows down enzymatic activity that can degrade muscle proteins before they even reach the washing stage.

For tropical fish species, scaling is also performed at this stage. The cleaned fish are then ready for filleting, where water nozzles or brush systems help remove remaining surface contaminants and prepare the flesh for mechanical deboning.

Heading, gutting, and filleting 🔗

Once cleaned, the fish undergoes heading and gutting – the removal of the head and internal organs. This step reduces the total fish weight significantly, as solid by-products such as heads (14-20%) and viscera (15-20%) account for a large portion of total fish body weight. These by-products are not wasted; they are collected separately for fishmeal, collagen extraction, or other value-added applications.

After heading and gutting, the fish body is filleted or cut into segments. Larger fish need to be cut into manageable sections before entering the deboning machine, whereas smaller fish can be processed whole. The fillets at this point still contain bones, cartilage, and connective tissue that need to be removed mechanically.

Mechanical deboning and mincing 🔗

The deboning step is where raw fish fillets are transformed into fine, bone-free mince. In surimi manufacturing, processors commonly use a roller-type meat separation process to mince and debone fish. This involves pressing different fish cuts against a rubber belt and a steel drum with 3-5 mm holes, sorting meat from skin, bones, cartilage, and other unwanted parts.

The perforated drum is the heart of the deboning machine. As fish material is fed into the machine, a rubber conveyor belt presses it against the rotating drum. The soft fish flesh is forced through the small holes in the drum and collected on the inside, while bones, skin, and cartilage – being too hard and large to pass through – remain on the outside and are scraped away. An inner scraper removes meat from the drum’s inner wall, while an outer scraper clears bones and skin from the roller surface, ensuring continuous, uninterrupted operation.

The diameter of the drum holes matters. For at-sea processing, 3-4 mm orifices provide optimum quality and yield retention. Shore-side plants may use 5-mm drums, while openings greater than 5 mm generate larger meat particles but make contamination removal difficult. For surimi destined for fine-textured products like fish balls or imitation crab, drum hole sizes of 2.5-3.0 mm are preferred to produce a smooth, consistent mince.

Why mince particle size matters 🔗

The size and uniformity of the mince directly affect how well it responds to washing and how well the final surimi forms a gel. A finer mince creates more surface area, which allows water to contact and extract unwanted soluble components more effectively during the washing stage. However, excessive mechanical action can generate heat through friction, which risks denaturing the proteins. Most industrial systems therefore include cooling mechanisms to maintain the mince at safe processing temperatures throughout deboning and mincing.

Washing: the most critical step in surimi processing 🔗

If deboning is the most technically impressive step, washing is unquestionably the most important. In order to remove water-soluble sarcoplasmic proteins (such as blood and enzymes), connective tissue, and fat, and to concentrate myofibrillar proteins, repeated cycles of washing and dewatering are performed.

Fish mince contains a complex mixture of proteins. Sarcoplasmic proteins are water-soluble components including blood pigments, enzymes, fat, and haem compounds. These must be removed because they interfere with gel formation, cause off-flavors, and accelerate lipid oxidation. Myofibrillar proteins – primarily myosin and actin – are the water-insoluble proteins responsible for surimi’s ability to form strong, elastic gels when heated. Washing selectively removes the former while retaining the latter.

The minced fish is washed multiple times – typically 2-3 cycles – with a mince-to-water ratio of 1:3 to eliminate impurities like blood and fat. Each wash cycle involves mixing the mince with chilled water, allowing the soluble components to dissolve into the water, and then separating the water from the mince through dewatering. The process continues until the mince becomes a nearly tasteless and odorless paste.

What washing removes – and what it must not 🔗

According to standard surimi processing protocols, the washing process is designed to remove: water-soluble sarcoplasmic proteins that do not contribute to gel formation; protease enzymes that would otherwise degrade the myofibrillar proteins during storage; blood and pigments that affect color; lipids that cause off-flavors and rancidity; and haem compounds responsible for lipid oxidation leading to protein denaturation.

However, washing must be carefully controlled. When sarcoplasmic proteins are completely removed after multiple wash cycles, any additional washing can cause myofibrillar protein loss. Studies have shown that a small amount of myosin is lost in the first wash water, with the loss increasing slightly in the second wash before stabilizing. Research on silver carp surimi confirms that repeated washing reduces fat content significantly and removes water-soluble proteins, but over-washing leads to protein yield reduction.

To prevent myofibrillar protein loss, processors control several variables: the number of wash cycles, the water-to-meat ratio, washing temperature, and salt concentration in the wash water. A concentration of 0.25%-1.0% NaCl in the washing solution is recommended to prevent the loss of myofibrillar proteins. The final wash often includes a dilute salt solution to help close subsequent wash cycles and improve dewatering efficiency.

Water temperature and its role in washing quality 🔗

All washing is performed with chilled water, typically below 10°C. This is non-negotiable. Fish mince is repeatedly washed with chilled water until a tasteless and odorless paste is obtained. Cold water slows enzyme activity, reduces the risk of protein denaturation, and inhibits bacterial growth during the extended washing process. Any rise in temperature at this stage can compromise both the safety and functional quality of the surimi.

Refining: removing residual impurities 🔗

After washing, the mince passes through a refining stage to remove any residual bones, skin fragments, scales, and connective tissue that escaped the deboning step. During refining, paddles or blades press the washed meat particles through a stainless-steel screen with 0.8-1.2 mm diameter holes, leaving impurities inside while the clean mince passes through. The rotation speed of the paddles and the screen size are key parameters determining how much impurity is removed. This step can be performed either before or after dewatering, depending on the plant setup.

Dewatering: adjusting moisture for quality 🔗

After washing and refining, the mince contains a high amount of absorbed water that must be removed before cryoprotectants can be added. Dewatering is the process of reducing the moisture content of the washed mince to an ideal level – typically 80-84%. Dewatering methods include manual presses, nylon mesh bags, centrifugation, and screw presses to reach the ideal moisture content.

The most common industrial method is the screw press, which mechanically squeezes water out of the mince as it passes through a tapered screw enclosed in a perforated drum. However, screw presses have limitations – they can cause significant loss of fine meat particles along with the expelled water. Upgrading to a decanter system can improve meat recovery significantly, as it separates meat from wash water more efficiently and requires only one washing step compared to at least two for a traditional screw press system – saving both water and operational costs.

Proper dewatering is essential not just for moisture control but also for the next processing steps. If the mince is too wet, cryoprotectants will be diluted and the product will not freeze or store correctly. If it is over-pressed and too dry, the proteins may be mechanically stressed and the gel-forming capacity of the final surimi can be reduced.

Why dewatering precision determines final quality 🔗

Washing is an important process for surimi production in which undesirable components in fish mince are removed while myofibrillar proteins are concentrated. However, dewatering is less effective for some fish species, which has led researchers to explore modified washing media. The use of dilute salt solutions – such as 0.45% NaCl combined with magnesium or calcium salts – in the final wash cycle has been shown to improve dewatering efficiency and gel-forming properties in certain fish species by inducing a mild salting-out effect on the proteins.

How the steps connect: the logic of surimi processing 🔗

Each processing step affects the quality and production yield of surimi. Temperature and time control during post-harvest, processing, and storage is a key element to keep surimi quality good and longer. The sequence – cleaning → heading and gutting → mechanical deboning → mincing → washing → refining → dewatering – is not arbitrary. Each stage is designed to progressively purify the fish muscle and concentrate the proteins that make surimi functionally unique.

Losses occur at every stage. Typically, 25-30% of the protein from the fish mince recovered by the meat separator is lost in the washing process and 3-5% in the refining process. Modern processing technologies – including decanter systems, enzymatic washing treatments, and real-time protein monitoring – aim to reduce these losses and improve overall yield without compromising the functional quality that defines good surimi.

Once dewatering is complete, the surimi mince is mixed with cryoprotectants (typically sucrose and sorbitol), packed into blocks, and frozen for storage or distribution. But the foundation for all of that final quality is built in the steps described above – from the first rinse of a fresh fish to the final pass through a screw press.

What do you think? Given that washing is both the most critical and most protein-lossy step in surimi production, how should processors balance protein recovery against purity when designing their wash cycles? And as global fish stocks for traditional surimi species like Alaska pollock come under pressure, how might processing technology need to adapt to work with fattier or less conventional fish species?

References

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