Can you eat fish that has been frozen for a year?
In this article, I will answer the question: “Can you eat fish that has been frozen for a year?” and I will explain the methods and the tips to properly store fish.
Can you eat fish that has been frozen for a year?
Yes, you can eat a fish that has been frozen for a year. But that may vary.
Although there are other factors that influence the fish shelf-life, such as the fish species and the stress suffered during catch, storage time and temperature and the amount of ice are some of the most important. In addition, the way that fish is stored (whole, filet, or gutted) also contributes to the final quality of the product and other factors related to the organism, capture method, and transport to the preparation/ processing industry should be considered for shelf-life extension (1).
Any frozen fish or shellfish will keep indefinitely; however, after a long period of storage, the flavor and texture will deteriorate. According to the US Department of Agriculture, raw frozen fish can be stored at -18°C for a maximum of 8 months for both lean and fatty fish. Cooked fish can be frozen for up to 3 months at 0°F / -17.8°C or less for maximum quality (2).
How does fish spoil?
After a fish dies, it begins to spoil quickly. This is shown in the slow formation of unpleasant flavors, softening of the meat, and finally significant losses of protein and fat-containing fluid. Spoilage can be delayed if the temperature is kept low enough. Other alterations are caused due to autolysis and lipid oxidation. Autolysis comprises the process of fish proteins and fats hydrolysis, by the action of proteolytic and lipolytic enzymes, respectively. The responsible enzymes for the autolysis of proteins and collagen, with consequent softening of refrigerated fish muscle in the postmortem phase, are cathepsin, calpain, and collagenase. The oxidation process involves oxygen and unsaturated lipids such as polyunsaturated fatty acids (1).
On the other hand, “rigor mortis” – which is a postmortem condition that causes the muscles to stiffen due to chemical alterations in muscle fibers – can occur within hours or days of fish death. It might affect handling and processing.
The reaction can be significant in some species, especially if the fish has not been cooled. Because muscles under stress tend to contract, some tissue may break, especially if the fish is handled violently, resulting in the flesh breaking and coming apart.
In this phase, connections between contractile proteins (actin and myosin) are established, resulting in muscle contraction, becoming rigid and inextensible. The rigor mortis resolution occurs after hours or more than a day, depending on the fish species, manipulation, size, physical condition and, mainly, the temperature and stress before death. Thus, with lower stress and temperature, the later it starts the longer the flesh stiness will be maintained, being the fish before or during this phase synonymous with high quality. With the rigor mortis resolution, the autolytic processes are initiated and, consequently, the fish deterioration will begin due to the creation of a favorable environment to bacterial growth (1).
If the muscles are cut before or during “rigor mortis”, they contract, shrinking the filets and giving them a chewy quality.
Freezing must be done rapidly in order to preserve the fish quality.
What is the effect of freezing on fish quality and shelf life?
Freezing is commonly employed to preserve the sensory and nutritional quality of fish.
Freezing is a good way to keep seafood fresh for long periods of time. In terms of color, taste, and texture, frozen fish preserved for up to three months in optimal conditions (low non-fluctuating temperature) cannot be distinguished from fresh fish.
Freezing will slow the biological, chemical, and physical deterioration of fish, thus it decreases the chemical reaction rates of enzymes and bacteria (3).
What are the advantages of freezing fish?
- Freezing your fish prevents it from spoiling:
Freezing does not destroy all bacteria and parasites, but it does stop the growth of bacteria and parasites that might cause food poisoning.
In addition, freezing fish preserves its flavor and texture while also extending its shelf life.
- Freezing prevents fish from losing nutrients:
Enzyme processes induce natural color changes, texture alterations, flavor deterioration, lipids oxidation, and water loss (1).
Aging is a natural process that affects all foods and is brought on by a variety of elements including light, heat, oxygen, and humidity.
The enzyme action is slowed by freezing fish, resulting in slower aging changes in texture, color, and flavor.
- Freezing extends shelf life of fish:
Fish can be frozen to extend their storage life, but it does not stop the aging process.
What are the downsides of fish freezing?
Although freezing is considered an effective method to preserve fish quality, it may have some downsides. Changes in color, texture, water retaining capacity, and intracellular/extracellular ice crystal formation effects on structure are all influenced by freezing.
- Crystal growth:
The quality parameters of frozen fish are affected by ice crystals generated after freezing. The formation of ice crystals in frozen fish can result in significant drip loss during thawing and cooking. Large damaging extracellular ice crystals can be formed, rupturing membranes, and disrupting the ultrastructure of cells and tissues. The rate of crystal growth is higher when slow freezing processes or multiple freeze/thaw cycles are used.
However, a rapid freezing rate reduces water migration into the extracellular space and, as a result, encourages the production of smaller intracellular ice which is less damaging to the structure. Fish frozen at higher freezing rates freeze more quickly and retain structural integrity in the intracellular muscle structure since more and smaller ice crystals are formed resulting in fewer freestanding or thermodynamically unstable water/ice molecules (3).
- Change in color and appearance:
Color or appearance is a physical characteristic that can change after freezing as a result of deterioration at the food surface. Pigment appearance can be affected by both chemical and biological processes. Color changes from autolytic and microbial activity in the fish degradation process may include the development of a yellowish color in the flesh or brown discoloration. Yellowish color in the flesh occurs in some frozen fish as a result of chromatograph disruption with consequent release and migration to the subcutaneous layer, as well as due to lipid oxidation which also causes brown discoloration (1).
Flesh-water binding characteristics and pigmentation within the skin give fish their appearance and color. Pigmentation can oxidize, resulting in darkening or fading, depending on the fish species. For instance, salmon meat has a pink pigmentation in its natural state, but the color tends to be lighter when frozen.
- Alteration of texture:
Texture is another quality criteria that may be harmed during fish freezing, which is due to ice crystal formation and recrystallization.
The texture of the fish may differ depending on the species. Fish texture is dependent on its fat and collagen contents and is a very important characteristic of fish muscle, which can be dry and hard in frozen products after thawing, revealing problems in the freeze system and/or temperature maintenance (1).
Fatty fish freezes relatively well, with little change in texture. When defrosted uncooked, lean fish turns to mush and rubber when cooked.
Protein denaturation in fish has also been connected to texture alterations during frozen storage (3).
- Lipids oxidation:
Lipid oxidation is a major factor that affects fish shelf life as it has an impact on flavor and nutritional value of fish .
Fish lipids are high in long-chain PUFA, which have been linked to improved health; nevertheless, they are highly vulnerable to oxidation, which decreases the nutritional, texture, and color quality of the fish. Many studies have shown that the amount of PUFA in food decreases as freezing time increases., especially arachidonic acid (C20:4n-6), eicosanoic acid (EPA), and docosahexaenoic acid (DHA; C22:6n3). Frozen storage reduced the PUFA and increased the saturated fatty acids (SFA) which indicated a substantial loss of nutritional value in fish (3).
In summary, freezing may slow the growth of microbes and bacteria in fish and extend shelf life of fish, but it can have some alterations in the organoleptic attributes such as color, appearance and texture. It should be noted that thawing must be done with caution in order to maintain the quality of the fish after freezing.
How to properly thaw frozen fish?
During the thawing process, bacteria begin to reproduce within the temperature ranges that are specific to each species. The higher the external temperature, the better the bacteria’s chances of spreading. As a result, defrosting at a lower temperature reduces the rate of multiplication.
There are two preferred methods for thawing frozen fish:
- Thawing in the refrigerator:
Place frozen fish in the refrigerator overnight to thaw properly. This will allow the fish to defrost more slowly and avoid spoilage.
The easiest way to keep the taste and texture of fish is to thaw it in the refrigerator.
The refrigerator should be kept at a temperature of 5°C or lower, as anything over this may allow bacteria to multiply.
As the fish thaws, keep it in its packaging or wrap it in paper and lay it on a dish to catch the drips. Keep it away from any ready-to-eat meals. To defrost, place in a bowl in the bottom of the fridge, away from any ready-to-eat meals. Refrigerate until completely defrosted.
- Thawing in cold water:
Cold water is a well-known and faster method of defrosting fish. For safety and flavor preservation, the fish must be kept in a sealed bag and submerged in water until defrosted. Allow to thaw completely. The average defrost time per pound is six to eight hours.
Thawing fish in the refrigerator or in cold water are proven to be the best methods to defrost fish. In addition, if the food will be cooked immediately thereafter – microwave it on the “defrost” setting and stop the defrost cycle while the fish is still icy but pliable (4).
Never defrost fish at room temperature or in warm or hot water, as germs can quickly proliferate under these conditions.
Other FAQs about Fish that you may be interested in.
In this article, I answered the question: “Can you eat fish that has been frozen for a year?” and I explained the potential alterations that can occur on frozen fish and the best ways to freeze it and thaw it.
Feel free to contact me for any further information related to this subject.
- Duarte, Ana M., et al. Quality Assessment of Chilled and Frozen Fish—Mini Review. Foods, 2020, 9, 1739.
- Food Keeper Data. United States Department of Agriculture.
- Dawson, Paul, Wesam Al-Jeddawi, and Nanne Remington. Effect of freezing on the shelf life of salmon. Int J Food Sci, 2018.
- Selecting and Serving Fresh and Frozen Seafood Safely. United States Department of Agriculture.