|Small-Scale Processing of Fish (ILO - WEP, 1982, 140 p.)|
|CHAPTER II. SALTING - DRYING - FERMENTING|
|VII. FERMENTED FISH PRODUCTS|
Fermentation involves the hydrolysis or breakdown of proteins into their constituents peptides and amino acids. The development of the characteristic odours and flavours of putrefaction is prevented by the addition of salt in varying but usually large amounts, similar to those used for pickled fish. The products are not dried after salting. In some circumstances, carbohydrates may be added which result in the formation of acids which further help to impart a characteristic flavour and odour as well as providing a further degree of preservation.
In general, three types of fermented fish products (Subba Rao, 1961) can be distinguished:
(i) Products in which the fish retain substantially their original form or in which large chunks are preserved (e.g. pedah siam (Thailand), makassar (Indonesia) and buro (Philippines));
(ii) Products in which the fish are reduced to a paste (e.g. ngapi (Burma), pra-hoc (Cambodia), belachan/trassi (Malaysia/Indonesia) and bagoong (Philippines));
(iii) Products in which the fish are reduced to a liquid (e.g. budu (Malaysia), patis (Philippines), nuoc-mam (Viet Nam) and nampla (Thailand)).
Few of these products and processes are found outside South-East Asia and, as with other methods of fish curing, traditional practices developed over many years predominate. These vary considerably from place to place, depending on local taste, raw materials available and care taken during processing. Many traditional products are of excellent quality and often rely on traditional skills which are difficult to emulate with modern processing methods. It is unclear whether the fermented fish products could be introduced successfully into other areas due to problems of consumer acceptability. The fermented products of South-East Asia are many and varied and, for the purposes of this review, it is only possible to cover a few of the more important products and processes.
VII.1.1. Makassar (Indonesia)
The fish species used in makassar are anchovies (Engraulis spp. and Stolephorus spp.). These are headed and placed in earthenware pots with an equal weight of salt. After three to four days, a red coloured rice product called angkhak is mixed with the fish and salt. Angkhak is made up of rice fermented with a mould organism imported from China (Monascus purpureus). Ragi (a Japanese preparation made from yeast and rice flour) is then added with spices. After a few days, the mixture becomes red and it is then packed into glass bottles for distribution. The composition of makassar fish includes, in most cases, 66% moisture, 16% protein, 1% fat and 17% ash.
Buro, which is made in the Philippines, is similar to makassar in that it is a rice-fish product mixed with angkhak. A fish often used in the production of buro is milk fish (Chanos chanos), a commonly cultured brackish water fish of the region. Freshwater species such as dalag (Ophiocephalus spp.) can also be used.
VII.1.2. Colombo cure (India)
This processing method, used in the South of India, utilises mackerel (Rastrelliger spp.), seer (Scomberomorus spp.) and large non-fatty sardines. The fish, which should be very fresh, are first gutted, gilled and washed in sea water. They are then mixed with dry salt in large concrete tanks, using a ratio of 1 part salt to 3 parts fish. Malabar tamarind, which is the dried fruit pulp of tamarind (called garikapuli, (Garcinia cambogia)) is added to the mixture in order to increase the acidity level of the fish preparation. As the fish tend to float on the blood pickle produced, they are weighed down with mats on which stones are placed. The fish can remain in the brine for two to four months prior to packing tightly in wooden barrels topped up with the blood pickle. The mango wood barrels, used for this purpose, are very large and can contain up to 5000 large mackerel weighing up to half a tonne. The storage life is well over a year and the product has a peculiar fruity odour. The flesh is flaky but firm. From a nutritional point of view, this product is very economical since the protein lost in the blood pickle is not wasted. After the fish have been unpacked from the barrels, the remaining pickle is used as a fish sauce.
In this processing method, the fish or shrimp are pounded with salt so that a paste results. The paste is then subject to periods of sun drying prior to packing in sealed containers for maturation. Moisture contents range from 35 to 50% so that almost half the water is lost during processing. Fish pastes represent a considerable portion of the protein intake of many people in South-East Asia (FAO, 1971), especially by the poorest sections of the population. In many fish pastes, carbohydrate-rich materials, such as fermented flour, bran or rice are added.
VII.2.1. Ngapi (Burma)
The raw material used in this product is small anchovy (Anchoviella comersonii) or shrimp (preferably the small planktonic types which give a better natural pink colour to the product). There are a number of methods for making ngapi, depending on the type of product required. In one process, which uses one part of salt to three parts of partially dried fish, the fish or shrimps are first washed in sea water and then dried for two days in the sun. About half of the required salt is then added to the fish and mixed in a bamboo basket. This mixture is pounded for several hours until a paste is formed. The paste is then packed into wooden tubs or boxes, care being taken that all air bubbles are removed. Fermentation takes place over 7 days and the paste is then removed, further pounded for three hours during which time the remaining salt is mixed in. The mixture is then spread out to dry in the sun for 3-5 hours. The product is repacked into tubs and the fermentation continues for about a month. After a third pounding, it can be packed for sale in cellophane or brown paper. Artificial dyes are often added to improve the colour. However, their use is not recommended as some may be toxic. When stored anaerobically in the tubs or earthenware pots, the product is said to keep for about 2 years. The average composition of a shrimp or fish ngapi is 43% moisture, 20% protein, 1% ammonia, 2% fat and 22% salt.
VII.2.2. Bagoong (Philippines)
Bagoong is one of the major preserved fish products of the Philippines where, in many communities, it constitutes a staple food. The product is also exported as far as the USA to the large ethnic Filipino community. A by-product of bagoong is patis, which is the exuded liquor from the fermentation process and is similar to the Vietnamese nuoc-mam.
Bagoong has a pasty consistency, and is reddish in colour with a slightly fishy cheese-like odour. It can be prepared from fish of the genera Stolephorus, Sardinella and Decapterus, and small shrimp. In the process described by Subba Rao (1961), the fish are washed in clean water, placed in a concrete or wooden vat and mixed thoroughly with salt. The ratio of salt to fish is about one third. The mixture of fish and salt is then transferred to earthenware jars, oil drums or cement tanks and either sealed immediately or, preferably, covered with cheese cloth for five days and then sealed. The sealed containers are held in the sun for one week and the product is then transferred to five gallon cans. These cans are, in turn, sealed by soldering of the lids, and the product is allowed to ferment further for between three months and one year.
The storage life of the product is many years, and the typical composition is not less than 40% total solids, 12.5% protein and 20-25% sodium chloride.
Fish sauces are basically water-extracted solutions of fully fermented fish and are used in a similar manner to soya bean sauce. Indeed, the manufacture and final composition of many fish sauces is similar to that of soya sauce, it being basically a mixture of protein breakdown products (i.e. peptides, amino acids, amines, etc.) in combination with high salt concentrations. Fish sauces may be of limited nutritional value (van Veen, 1965) as their high salt content precludes bulk consumption. However, in some regions, consumption is surprisingly high and in Viet Nam the sauce nuoc-mam can provide up to 20% of the daily protein intake. Fish sacues are rich in hydrolysed proteins and minerals (e.g. sodium chloride and calcium salts) and can be an important source of calcium in the diet.
VII.3.1. Nuoc-mam (Viet Nam)
Nuoc-mam is by far the most important fish sauce in South East Asia, many thousands of tonnes being produced each year, principally in the coastal regions of Viet Nam, Thailand and Cambodia. Nuoc-mam of good quality is a fairly stable, clear dark brown or amber liquid with a distinctive odour and flavour. The lower quality nuoc-mam may, however, have an unpleasant odour and a reduced storage life. Quite often, additional ingredients are added in order to darken the liquid and improve the flavour of the product. These include such materials as caramel, roasted rice, molasses and roasted or boiled corn. Due to its widespread distribution and consumption, legislation has been introduced in some countries in order to guarantee set quality standards.
The fish species used in the production of nuoc-mam are usually of the genera Stolephorus, Engraulis, Dorosoma and Decapterus and clupeoids. Nuoc-mam can also be prepared from shrimp. The processing method is similar to that of bagoong except that the fermentation is generally protracted and the product is the exudate rather than the solid fraction. The actual process varies according to scale. In the small scale operations, whole fish are kneaded lightly by hand, mixed with salt in earthenware pots and buried in the ground for a few months. The nuoc-mam is the clear liquid which settles on top and is carefully decanted off. In the large scale operations the fish (whole and unwashed) are piled, with salt spread between layers, in timber vats. 4 parts of salt to 6 parts fish should be used for this purpose. After three days, the blood pickle (nuoc-boi) is allowed to flow out slowly over a 3-day period into another recipient. The fish are then trampled by foot until a flat surface is obtained. The latter is covered with coconut leaves over which are set two semi-circular bamboo trays, the whole system being wedged down tightly. The nuoc-boi is then poured back over the fish until a 10 cm liquid layer is formed on the top of the trays. It is then left to mature for four months to a year depending on the species of fish. After maturation, the pickle which is run off is the top quality nuoc-mam. The trays and leaves are removed, and fresh salt is added to the top layer of the fish residue. Fresh brine is also added to obtain a lower quality of nuoc-mam.
The yield varies from 2 to 6 parts of nuoc-mam from 1 part of fish, the residual mass being used as fertiliser. Nuoc-mam is normally packed in bottles but may also be stored in earthenware pots.
VII.3.2. Other fish sauces
A number of other fish sauces are also produced in South-East Asia in large quantities. Patis (Philippines) is produced from the bagoong process and is similar to nuoc-mam. Nam-pla is made in Thailand, the preferred fish species being Stolephorus spp. Production of the latter is similar to that of nuoc-mam although less salt is used (i.e. 1 part salt to 4 parts fish). The process may take from 6 to 36 months to complete depending on the quality required. In Malaysia, a sauce known as budu is made from small anchovies. Production involves mixing 1 part of salt and 5 parts of fish in eartheware pots together with tamarind and palm sugar. A dark, sweet-smelling sauce results after 6 months of fermentation. The product has a storage life of 2 years or more.
There are almost as many traditional methods of packaging fermented fish as there are ways of making it. A number of these have been mentioned already, for example earthenware pots, oil cans, drums, glass bottles, wooden barrels, etc. In the past, the latter have been used because of their low cost but nowadays plastic containers tend to replace the traditional containers. The most important function of improved packaging for fermented fish products is that the containers should be air-tight, helping to develop and maintain the anaerobic conditions required for good fermentation and storage. All containers should also, of course, be thoroughly cleaned prior to use. As the major advantage of these products is their low cost, the type of packaging is necessarily restricted. Glass bottles are used for the better quality products, and vacuum packed sealed foil/plastic laminated products pouches might be used in the future.