Boiled fish products

Boiling fish in water is a method of short-term preservation used in many countries especially in South East Asia; although the method is used in other parts of the world, it is in fact only of major commercial significance in South East Asia. The shelf life of the products varies from one or two days to several months depending on the method of processing.

Basic method

The action of boiling fish in water at normal temperatures and pressures denatures (cooks) the proteins and enzymes and kills many of the bacteria present on the fish. The normal spoilage that occurs in a dead fish is thus stopped or drastically reduced. With the normal methods of packaging which are employed with cooked fish, they are very soon contaminated with bacteria again and spoilage can thus begin. Boiling fish in water will not produce a completely sterile product and, even if they were packed in completely sealed packaging, spoilage would still occur.

Very many variations of the basic method of preparation are used, depending on the raw material available, the required shelf life and consumer preferences. Often salt is added before, during or after processing; high levels of salt in the final product will help to extend the shelf life. In hot humid countries, therefore, where drying fish may be difficult, boiling may allow distribution of the catch to market in an acceptable condition with simple, low-cost facilities and equipment.

Products where the fish are boiled for a relatively short time with little salt should be treated in the same way as fresh fish. Where fish are cooked for several hours with plenty of salt, the product will not resemble fresh fish and can be treated in a similar manner to other salted fish products.

Variety of production methods in Asia

Some idea of the range of boiled fish products produced in Asia is given from the outline of methods below.

Cambodia

Raw material: Eleutheronema, Stromateus, Polynemus, Cybium, Sardinella spp.

Processing method: Immerse the fish in boiling brine (5 kg NaCI per 20 litres sea water) for 3 minutes. The fish are boiled in small baskets which are used both for cooking and distribution.

Storage life: 1-3 days.

Malaysia

Raw material: Rastrelliger sp. (kembung)

Processing method:	1 Wash the fish in sea water.
	2 Immerse them in saturated brine for 3 - 4 hours.
	3 Arrange the salted fish in bamboo baskets.
	4 Immerse the baskets in boiling brine containing 25 - 34 per cent salt.
	5 Allow the baskets to cool.
	6 Store in a cold room.

Yield: Approximately 70 per cent of raw material weight.

Packaging: The processing baskets.

The Philippines

Raw material: Tulingan, frigate mackerel etc.

Processing method:	1 Prepare the fish. They may or may not be gutted; the side of the fish
	may be cut.
	2 Rub salt into the fish.
	3 Place the fish on a mat in a clay pot.
	4 Fill to the top of the pot with fish.
	5 Heat the pot gently until the fish are steamed.

Packaging: The processing pot.

Indonesia

In Indonesia, various boiled fish products are produced, generally known as pindang. One of the methods used is as follows:

Raw material: Many species, including sharks, but commonly Rastrelliger (kembung), Decapterus (lejang), Euthynnus (tonkol) and Caranx spp.

Processing method:	1 Gut and cut the fish to fit the container; small fish may not be gutted.
	2 Wash.
	3 Arrange the fish in the containers (clay pots or metal bowls) in alternating layers of fish and salt; the ratio of fish to salt varies between 20:1 and 3:1 depending on the shelf life and taste required.
	4 Add a little water.
	5 Heat above a fire (wood or oil) until nearly cooked.
	6 Drain most of the liquid from the bottom of the container.
	7 Add more salt to fish on the surface and cook until no free water remains in the bottom of the container.
	8 Seal the top of the container with leaves or paper.

Yield: 80 - 90 per cent of raw material weight.

Packaging: The product is distributed in the processing container.

Shelf life: May be from a few days to 3 months depending on the quantity of salt and effectiveness of sealing the container.

Chemical composition: For Caranx leptolepis,

Moisture	66.5	per cent
Protein	22.3	per cent
Fat	2.5	per cent
Salt	0.9	per cent

Research: Some investigation has been undertaken into sterilising the clay pots before cooking. Rubber rings have also been used to seal the top of the container and wax has been used to coat the outside of the pot to seal it: the shelf life may then be extended up to 9 months.

Some concern has been expressed in Indonesia over the public health and safety of boiled fish and some cases of sickness, or even death, have been allegedly caused by eating pindang. Traditionally, clay pots have been used for cooking and distribution but recently these have been replaced, to some extent, by pots made from galvanised sheet. It has been suggested that the zinc of the galvanising may contaminate the fish, and also there may be contamination from the lead used to solder the seams. In addition, insufficient cooking or too little salt allows the growth of harmful micro-organisms. Although some work has been carried out to extend the shelf life of pindang, it has been proposed that a detailed study of processing, packaging, storage and spoilage is needed.

Conclusion

Boiled products are acceptable to large numbers of consumers in South East Asia and the process used may be suitable for introduction to other tropical countries where conditions of high temperature and humidity make normal salting and sun drying difficult for part or all of the year.