Fish processing

Fish processing is the series of steps taken between catching an aquatic organism and delivering the final product to a customer.

This industry includes fish caught in wild fisheries and those harvested from aquaculture, which is fish farming. Because fish are highly perishable, they can deteriorate quickly. The central goal of all processing is to prevent this spoilage. This ensures the fish retains its nutritional value and desirable quality.

Large companies often operate their own fishing fleets or farming operations. They typically sell their products to grocery chains or intermediaries.

Processing is often divided into several distinct stages. Fish handling is the preliminary work done on raw fish. This includes sorting, grading, bleeding, gutting, and washing the catch.

Primary processing follows, which involves filleting and freezing fresh fish for retail or catering. Secondary processing is more complex. It produces chilled, frozen, or canned products for the market. Some modern processing also focuses on adding value by creating ready-to-eat products. These require very little preparation by the consumer.

When fish are first caught, they must undergo immediate preprocessing. This ensures they remain in a fresh and undamaged condition. On a fishing vessel, this might involve transferring the catch from nets or lines to storage. The specific order of these steps depends on the fish species and the size of the vessel. Operations can be manual or automated. In modern industrial fisheries, equipment is designed to reduce rough handling. This also helps prevent injuries to workers from heavy lifting or poor working positions.

One way to ensure freshness is to keep fish alive until they are ready for consumption. This is a common practice worldwide. In aquaculture, fish can be kept in floating cages, wells, or ponds. For example, in China, floating cages are made from woven palm baskets. In South America, simple fish yards are used in river backwaters. To keep live fish healthy, workers must control the water. They remove sick fish and lower the water temperature. They may also starve the fish to reduce their metabolic rate. This prevents the water from becoming toxic with ammonia, nitrite, or carbon dioxide.

Preservation techniques are used to stop spoilage bacteria from growing. These bacteria produce the unpleasant odors and flavors found in spoiled fish. To thrive, these bacteria need specific conditions: the right temperature, water, oxygen, and a non-acidic environment.

One major method is controlling temperature. Refrigeration drops temperatures to about 0 °C. Freezing drops them below -18 °C.

On ships, fish are cooled with mechanical refrigeration or ice. Some use slurry ice, which is a mix of ice crystals and a freezing point depressant like salt. A newer technology is pumpable ice, which flows like water and cools fish faster than solid ice.

Another method is controlling water activity, or the amount of available water in the flesh. Bacteria need this water to trigger spoilage. Traditional methods include drying, salting, and smoking. Solar drying is a very simple form of this. More modern methods include freeze-drying or using humectants to bind water.

Physical control is also possible through heat or ionizing irradiation. Microwave heating or cooking can pasteurize or sterilize products. Sterilized products are stable at temperatures up to 40 °C if they are kept in metal cans or pouches.

Chemical and atmospheric controls provide further protection. Biopreservation involves adding antimicrobials or increasing acidity. Most bacteria stop multiplying when the pH level is less than 4.5. This can be done through fermentation or by adding acids like citric or lactic acid.

Another method is reducing oxygen. Spoilage bacteria often need oxygen to function. This is achieved through vacuum packing or using modified atmospheres with specific levels of nitrogen and carbon dioxide. Often, processors combine these methods. Using multiple techniques at once can improve preservation without using extreme heat that might damage nutrients.