The Journey of Sea Herring: From Ocean to Table

Sea herring, a versatile and widely utilized fish species, plays a significant role in both domestic and international markets. Larger herring are often exported, catering to a global demand for human consumption. Meanwhile, smaller herring are typically processed into canned sardines, a staple in many households.

The preparation of smaller herring for canning is meticulous. Initially, these fish are held in a purse seine for over 24 hours to ensure their stomachs are free from feed. This crucial step prevents enzyme reactions that could degrade the fish's quality. Once the herring are ready, they are loaded onto boats using a large vacuum pump and salted to begin the preservation process.

At the processing plant, the fish undergo further salting after being beheaded and eviscerated. Following this, they are reheated and placed in small rectangular cans. The herring are then steamed for 18-20 minutes to ensure proper cooking. After steaming, the liquid in the cans is drained and replaced with vegetable oil, tomato sauce, or mustard sauce, depending on the desired final product. The cans are sealed, heat-processed, and cooled, resulting in a shelf-stable product.

Larger herring are also canned, often whole, in larger oval cans with tomato sauce. Alternatively, they can be cut into bite-sized pieces and packed similarly. These products are designed to be shelf-stable, offering a convenient and long-lasting food source.

Beyond canning, herring are also pickled. This process involves using salt, vinegar, sugar, and spices, with additional ingredients like sour cream and onions sometimes added before sealing in glass jars. Pickled herring variants include rollmops (pickled herring strips wrapped around pickles or onions) and kippered herring (salted and lightly smoked). These products, however, require refrigeration to maintain their quality.

Another preservation method involves heavily salting and smoking herring, producing a shelf-stable product. Additionally, the scales from herring skins are collected in large quantities to manufacture pearl essence, a valuable by-product used in various industries.

In summary, sea herring's journey from ocean to table encompasses a range of processing techniques, each ensuring the fish's quality and longevity. Whether canned, pickled, or smoked, herring provides a versatile and essential food source, demonstrating its global significance and multifaceted utility.
The Journey of Sea Herring: From Ocean to Table

Fish canning process

The canning of fishery products may be divided into a number of definite steps applying equally well to all types, although details of methods and processes vary with the individual product.

Defrosting
If frozen fish are to be processed, they must first be defrosted. The thawing process involves the elevation of temperature of the fish to 0 °C, at which temperature it may be manually cut or otherwise prepared as necessary.

Butchering
The splitting and evisceration process is normally the only butchering operation

performed on the tuna while it is in the raw condition. This operation involves the scaling, evisceration, removal of parts not to be canned, and thorough washing in either salt or fresh water. The scaling may be done by hand with serrated-edge scrapers, the edges of knives or other means devised by the technician.

Salmon is traditionally filled into cans in the raw state. After grading, fish are fed into an iron chink butchering machine for the automatic removal of head, fins and viscera.

Pre-cooking
Sardines, mackerels and tuna are normally pre-cooked prior to sterilization. The object of pre-cooking, particularly in the case of tuna, is to facilitate the removal of flesh from the carcass.

Typically, sardines are packed into quarter club cans, which are placed in square plastic trays. The trays may hold some 4 x 7 cans each. A thin sheet of metal is placed over the tray and the whole inverted and placed on racks on a trolley which is then wheeled into a batch pre-cooker.

Functions of pre-cooking:
• Firm texture of fish
• Reduction in bacterial load
• Inhibition of enzymatic reaction
• Shrinkage for better filling
• Removal of cellular gases

The time for pre-cooking in steam at a temperature of 105 °C is about 30 minutes depending on the size of the fish.

Can filling
Before being canned, the cans and jars are rinsed with water under pressure of steam before being filled.

Filling may be accomplished either by hand or by machine. Can filling in large tuna factories is undertaken by high-speed machinery. The tuna is formed into a tube within the machine and sliced to the correct height and fill weight on presentation to the can. Smaller fish and meat scraps are generally canned as flakes after being pressed into moulds.

Sardines are traditionally filled manually into cans prior to pre-cooking, but automatic machines are also available.

Mackerel are processed in both rectangular and cylindrical cans and the filling operation may take place manually or by suitable machinery according to the size of the operation.

Covering liquid, oil, brine or sauce is added to fish within shallow cans to overflowing. The excess liquid is screened and returned to the filling head.

Fish and the liquid added to the can should be packed tightly to prevent it from shaking around and braking up into undesirable looking pieces, requires the fish to be packed in an orderly fashion.

The weight is checked at this point to prevent excessive filling that could lead to the foodstuff not being processed appropriately, swelling of the tin or even bursting of the seams.

The can may then be closed using steam flow to remove air and provide a vacuum within the can. Then the can is sealed. The sealed cans are cleaned to eliminate any remarks of filter and they are prepared for sterilization.

Heat Processing
Fish products and other low-acid foods are usually processed in steam at temperatures of 115° to 120°F. This operation is usually carried out in heavy metal airtight receptacles (retort) that will stand internal pressures of 20 and 30 pounds or more to the square inch.

Can coding
Coding may be applied to the ends of cans by use of embossing machines, or more frequently nowadays, by the use of ink jet machines.
Fish canning process

Canning of fish

Canning is a method of storing food in airtight containers in a way that destroys potentially harmful microorganisms such as bacteria.

Most canned fish products are composed of ingredients that result in finished product with pH above 4.6 and water activity greater than 0.85.

These characteristics result in canned fish products being considered ‘low-acid canned food’. Canned fish have a shelf life of one year while frozen, oily fish should be used within two months.

Canned fish is conventionally covered with a liquid such as brine, vegetables oil tomato sauce or other sauces.

The canning process depends on the size of the fish. Small fish species such as sardines and pilchards are generally canned whole, with only the heads and tails removed. These whole-fish products are cooked in the can after it has been filled with brine or oil.

Canned fish is that it’s already cooked and ready for many easy dishes such as fish cakes, quiche, loaf, salads, sandwiches and appetizers.
Canning of fish

Tuna fish canning

At the processing plant, the fish are thawed in holding rooms at ambient temperature or in tanks with running water.

When thawed, the fish are eviscerated and washed. They are then cooked in steam, under pressure, and then cooled.

Precooking removes most of the strong flavored oils. The strong flavor of dark tuna flesh affects the delicate flavor of white flesh. When cooled, the heads and skins are removed.

The fish then cut longitudinally after which all bones and the dark meat are removed.

The white meat is shaped, mechanically into a cylinder, feed into cans and cut to length. To pack chunk style tuna, pieces are filled into cans with adjustable filler.

Vegetable oil or a broth containing hydrolyzed vegetable protein in water is metered into the cans, are then heated in steam, sealed, heat-processed. The sterilized cans are cooled in ruining water, wiped and kept in a cool place 10-15.5 °C. The cans then are labeled and stored.
Tuna fish canning

Light tuna

Skipjack - leaner than albacore tune; it is the most commonly used tuna for canning. Skipjack tuna are highly migratory and have been fished by any different countries such as the US, Mexico, Ecuador, France and Spain.

Skipjack tuna

Yellowfin – larger and leaner than albacore; it has pale pink flesh and is the second most popular species of tuna used in canning.  It is found throughout the world’s tropical and subtropical seas, except the Mediterranean.

It is canned and marketed as light tuna, but it is also an important component of sushi and sashimi.

Bigeye – similar to yellowfin; it has a milder flavor than skipjack or yellowfin and is frequently used in canning. It is a tropical and subtropical species with separate stocks in the Atlantic, India, Western and Central Pacific and Eastern Pacific Oceans.

Together yellowfin tuna and skipjack tuna account for most of the world’s canned light tuna, but chunk light tuna may refer to a number of species: bigeye, yellowfin, skipjack or tongol tuna.
Light tuna

White tuna

American demand for fresh tuna grew tremendously toward the end of the twentieth century, and fisherman scoured the seas, searching for the finest tuna.

Tuna is canned solid and in chunks. About ten different species of tuna are canned, but labels usually distinguish only between ‘white tuna’ and ‘light tuna’.

Albacore
Albacore is high in fat and rich in EPA/DHA; it has the whitest flesh and is typically referred to as white tune; it is eaten both canned and fresh.

It is a member of the Scombridae family of tuna and mackerel. The albacore is an excellent light-tackle gamefish.

The average weight for albacore is between 1-0 and 25 pounds. Albacore generally contain more methylmercury than other types of tuna and may also contain more lipophilic compounds.

Northern Bluefin 
The Northern Bluefin tuna occurs in commercial quantities in the Atlantic and Pacific Oceans, from 70 °N to 25 °N and to a smaller extent south of the equator in the Pacific. The fish is high in fat and EPA/DHA; it is a slow-growing and thus rarer species than albacore and has a very high-quality meat; its major market is Japan where it is used for sashimi.

Southern Bluefin 
Stocks are in decline and thus it is harder to obtain than other tunas. It is the most expensive fresh tuna. They are distributed only in southern hemisphere and mainly inhabit cold waters around 40 °S.

This is unique species of tuna, in that one stock is distributed throughout the three major oceans, Pacific, Indian and Atlantic.
White tuna

Canning of fish

Fish used for canning include sardine, anchovy, pilchard, tuna and mackerel.

The fish is received and unloaded in the plant by electric winches, washed, put in brine and transported to the heading, gutting and cutting machines.

Fish for canning must be of highest quality. In comparison with most animal products, fish spoil much more rapidly, and pelagic fish tend to be more susceptible than other species.

Small sized fish species are canned whole, whereas medium seized species are first nobbed and then cut into pieces before canning.  The can are weighted, the tops sealed and placed in a retort for cooking.

The number of stages, or their order within the canning process, can vary according to whether large or small species are being used, whether continuous or batch processes have been chosen, whether manual or mechanical labor is being utilized.
Canning of fish