Food Preservation: Drying, Salting, or Freezing Fish
Reasons for Preserving Fish
The majority of fish are harvested from the wild in streams and oceans. Some high-value fish are farmed so that the reproductive cycle of the fish can be managed according to demand. However, most fish are caught in its natural environment and the catch weight of each fishing expedition is unpredictable. The life-cycle and restocking rate of each species in the wild can vary considerably.
For as long as man has been fishing, whenever the catch has been substantial, excess fish have been preserved and saved for less plentiful times. The earliest methods included drying the fish under the sun (in hot climates) or surrounding the fish with packed ice (in colder climates).
Food and Bacterial Growth
Effective methods of food preservation are essential for humans, as there are times of the year when fresh food is not readily available. Preserving food when it is plentiful means that there need be fewer periods when you have to go without. This applies to developed societies as well as more primitive communities.
People have become used to buying frozen and chilled foods from the supermarket and these are now common methods of making food last longer. However, methods of preserving food also include cooking, drying, and salting. They all work by preventing bacterial growth and hence the process of decay in the food. In order to grow and multiply, bacteria need moisture, warmth and time. By removing one of the conditions for bacterial growth, the food can be made to last longer.
Preserving Food at Home
1. How to Preserve Fish: Salting and Sun-drying
In some countries electricity is a recent luxury. The oldest methods to preserve fish are therefore by salting or dehydrating the food. Salting fish is a way of drying the flesh because it draws out moisture and so prevents bacterial growth. Drying under the sun is possible in some places. In cooler climates water is removed using dehydrator machines. This can be done at a domestic level as well as in large industrial sized dehydration plants.
When done properly, both sun-dried and salted fish can remain edible for many months. Before cooking, the fish is rehydrated by soaking overnight in potable water. The video below shows how fish are salted and then sun dried in a sunny country like Brazil.
2. Ways to Preserve Fish: Freezing
Freezing preserves fresh fish by locking any water present into a solid form (i.e. ice). This makes the water unavailable to bacteria and thus prevent bacterial growth. Unfortunately one of the side-effects of freezing fish can be that frozen water crystals pierce the cell walls. This can make the defrosted fish mushy in texture. To limit this type of cell damage fish should be frozen using a process known as quick freeze-drying.
Freezer burn can also be a problem if the processed fish is not protected once frozen. If left for too long in a freezer, the intense cold can cause further drying and damage to the surface of the flesh resulting in a “burn”. This can be avoided by vacuum packing the fish before freezing it. Alternatively the fish can be packed in a sauce so that the drying effect of freezing acts on the sauce rather than on the fish itself. The video below demonstrates how to freeze fish effectively and how to avoid it being affected by freezer burn.
How to Freeze Fish and Avoid Freezer Burn
Benefits of Freezing Versus Salting or Drying Methods
Frozen fish tends to be more popular with consumers than salted and dried fish because freezing does not affect its flavor. Frozen fish can be cooked straight from the freezer with little loss of quality compared to the fresh product. Salted and dried fish on the other hand, needs to be soaked overnight in water to allow the flesh to rehydrate. Even if the soak water is changed several times, the fish still retains a salty taste that isn't found in fresh fish.
Manufacturers recommend you eat their frozen fish within three months of purchase, but you could leave it in the freezer for up to six months with no ill effects. Salting or drying the fish can make it last up to twelve months providing it is kept in cool dry conditions. If you combine the two methods i.e. freezing an already salted or dried fish, there is little to be gained. The taste of the fish has already been changed by the dehydration process. Placing it into the freezer will not regain that fresh fish taste.
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Don't Freeze Fish That is Already Dried or Salted
Researchers in Reykjavik, Iceland carried out controlled experiments to measure the effect of freezing on already dehydrated cod fish. They looked at changes in physical weight of fish stored for up to six weeks at a variety of cold storage temperatures.
The effects of storing and drying on the quality of cured salted cod were studied in 2007 at the United Nations University, Reykjavik, Iceland. The conclusions were clear. At the lowest temperatures i.e. at -18 C and -24° C water content of the fish was greatly reduced and as a result, the fish lost weight over the six weeks of the experiment. There is therefore not only no need to freeze fish that has already been dried or salted, but freezing such fish is likely to result in deterioration in eating quality.
3. Reduced Oxygen Method or Vacuum Packing
Freezing, drying and salting are not the only way that fish can be preserved for later eating. Vacuum packing of fish is often carried out in conjunction with one of these methods, but it can be done on its own.
Vacuum packing is simple to do at home if you use the correct equipment. The vacuum sealer machine sucks all the air (oxygen) out of the vacuum bag and then heat seals it. The video below gives a demonstration of how to vacuum pack fish at home. Once hermetically sealed, the fish will stay fresh for a week in the fridge and up to year in your freezer.
This method of preserving fish is especially useful if you are a keen leisure fisherman. Success as an amateur fisherman tends to result in either feast or famine. Freezing a bumper catch after having vacuum packed it first will increase its freezer storage life from six months (without vacuum packing) to one year (with vacuum packing).