Drying fish as a method of preservation has been used for at least 5000 years in Africa. There are hieroglyphs in Egypt describing the splitting and drying of fish that are at least that old, writes Mr Piers.
Exactly the same methods are still in use today, and the product is a highly esteemed part of traditional African diets.
Some technical factors have influence on the success of any fish processing operation, and the final product should have high market acceptance. Some important points to bear in mind are:
1. Simple systems work best
2. Cost is a major factor in adoption of technology
3. Gas properties - hot air rises
4. Good flow of air is important to remove moisture
5. Fish should be positioned to drip excess water
6. Wood retains bacteria and should be avoided
7. Wire mesh grids are expensive and difficult to clean
After examining a recently published FAO Guide several points have been noted. These are discussed below and some alternatives suggested.
The picture above from the FAO document shows fish laid out on a metal grid for smoking. From many years of experience with this process, several serious disadvantages of using grids have been identified. They are:
1. The fish sticks to the grid when being smoked.
2. It is necessary to turn the fish over to ensure equal smoking on both sides.
3. When turning over, the fish breaks up and losses are incurred, and the product is damaged.
4. The layer of fish blocks the free flow of air through the fish.
5. Small pockets of liquid are trapped on top of the fish and provide areas for bacteria to multiply.
Besides operational problems, some of the grids shown have wooden frames. It is an established fact that wood implements and trays harbor bacteria that are not eliminated by washing, and that then can be transferred from one batch of fish to the next, thereby hastening their proliferation. It is for that reason that wooden fish crates were banned many years ago in the EU.
The grids used in this smoker are also not very suitable. They are manufactured from expanded sheet metal, and this process causes the formation of extremely sharp edges where the metal has been sheared. The consequences of this are:
1. Risk of injury to workers as they have to manually turn the fish over by hand.
2. Many small corners where thorough cleaning is impossible, and dangerous.
These are visible in the illustrations below.
Note the fish touching each other, and the wooden frame, in the picture above.
By way of example, a different system was constructed and successfully used for many years by this author. Unfortunately original pictures do not exist, so an effort has been made to illustrate the principle generally.
Initially an old galvanized steel water tank was obtained free of charge as it could no longer hold water and was replaced. The type is shown below:
These are very common in Africa, and many of them are now being replaced with plastic tanks that do not rust. Obviously a small leak is a problem if they are used for water retention, but not a problem if being used as a smoker.
Once constructed as per the diagram below, instead of using grids the fish are hung on metal rods inside the container as shown. This has numerous advantages such as:
- Cost. The cost of construction materials is minimal, comprising of the tank (possibly obtained for free!), the metal rods made from normal concrete reinforcing material which is universally available and cheap, and the chimney and flue.
- The heat and smoke are not lost due to opening for access. Rods are inserted and removed very quickly with minimum effort, and only once per cycle. When the rod is removed, many fish are handled simultaneously thus saving labour.
- The metal naturally radiates excessive heat should the fire be temporarily too hot, so a self regulating system is established. Once set up, the fire does not need to be attended.
- If set up properly, the fish do not touch each other, or metal, or wood that has had fish on it previously. This is the major cause of bacterial contamination and proliferation.
- The fish hanging vertically allows them to drip any fluids or fats, thus facilitating much more rapid drying. A simple drip tray without openings can be installed inside on the floor.
- With this system high volumes of fish can be smoked simultaneously without impeding the flow of heat and air. This due to the hanging system and the natural shape of the fish.
- Maintainence, especially cleaning is minimal. Rods can be soaked and disinfected easily.
Both horizontally and vertically separation of the fish is easily achieved as shown below. The length of the flue will determine the temperature of the air and smoke entering the chamber.
The top rods are secured to the top (roof) and lower ones hung from each other with simple hooks. This is a very efficient system allowing unimpeded airflow and rapid drying.
Smoke-dried products produced with this system are of a very high quality, very well received by African consumers, and it requires extremely small amounts of wood fuel. Whole logs can be used, saving labour on woodcutting. The cost is well within the means of many small-scale processors and construction materials almost universally available in Africa.
For more information, contact Adrian Piers at firstname.lastname@example.org
You might also be interested in:
- A Guide to Smoking for Fish Preservation
- New Fish Smoking Technology to Benefit Ghana
- New Fish Drying Technology Boosts Livelihoods in Ivorian Town