8.0 PROCESSING DIFFERENT SPECIES

Of all the varieties of whitefish, the lake Whitefish is the most important freshwater commercial species in Canada. It is widely distributed from the West Coast across the country and north into the (Yukon and Alaska). It is caught commercially in gillnets or trapnets. It is also a popular sport fish. As stocks are depleting, the total yearly Canadian harvest dropped from 8,000 tons to 4,000 tons in the nineties. It is a year round fisheries. Of this amount, over half is caught when the fish congregate and move to shallower wa-ters for spawning in August - November. Spawning starts when the water temperatures fall to 7-8°C and this part of the harvest is the source of the mature roe which is fit for caviar production. Commercially caught, spawner size whitefish range from 1.5 to 4 Ibs. (3 to 7 years in age) and yield on average 14% of female weight as roe. Utilization of whitefish roe and many other ordinary fish species roe has a 150 year history in the south of Russia, where this caviar was called 'chastikovaya ikra', i.e. caviar of ordinary size and species of freshwater fish, as opposed to caviar produced from 'noble fish', the Russian 'krasnaya ikra', e.g. sturgeon or salmon caviar.

Lumpfish and whitefish egg size is approximately the same but as opposed to lumpfish, whitefish caviar is mainly processed without dyeing and almost exclusively in a one step process, i.e. without preliminary heavy salting. It retains its natural yellow-goldish shade. A sizeable caviar industry started in Europe and North America in the 1930's. A fresh start was given to the development of whitefish caviar by the comprehensive re-search in the 1970's done by the Western Region of the Department of Fisheries and Oceans in Winnipeg. The low salted, retail packed (50 g) caviar from Manitoba lakes earned a Gold Medal in the 1980 World Culinary Olympics, in Frankfurt, Germany. The product is popular and prices are close to those of salmon caviar.

The logistics of whitefish roe harvesting, as well as the logistics of other freshwater fish, is different from lumpfish roe harvesting in that small boat fishing takes place close to the processing site and fresh roe delivery is a lesser problem. There is no need to proc-ess a highly salted bulk product and then desalt and repack it. In Canada the prevailing tradition is that fishermen themselves extract the ovaries, screen and sometimes salt them on the fishing grounds. The bulk caviar is then delivered to the processor, who may flavour, dye and repack the product. The various options of whitefish caviar proc-essing technology are similar to lumpfish technological, options, see Figure 8-3.
Some differences in the technology recommended by the DFO Winnipeg Laboratory are given below.

Whitefish eggs easily withstand the washing procedures. Washing of screened eggs is recommended using the floatation principle.

Whitefish scales are easily detached when fish is handled and the loose scales of white-fish often contaminate the bulk of the screened eggs, which creates a major problem. A secondary washing-screening process to get rid of any fish scales or other particles is done using a dipnet with a mesh size slightly larger than the egg size, see Figure 8-4. The scales remain in the dipnet and the eggs fall to the bottom of the tank.

FIGURE 8-4: Secondary Washing-screening

1 - Screen, 2 - Remaining scales, 3 - Unscreened eggs, 4 - Cleaned eggs
5 - Mesh tray

A popular method to segregate impurities from small lots consist of rolling salted eggs over cheese cloth. By rolling them back and forth, eggs are both drained and impurities are caught by the cheese cloth. The cloth has to be rinsed as soon as it is soiled.

After draining for about an hour, eggs are examined again for cleanliness and passed on for salting. Stirring time of eggs with salt-preservative mix ranges from 1 to 25 minutes. Eggs with a thick membrane are stirred for a longer time. At the beginning the egg mass is foaming and gets very liquid. However, soon the egg mass becomes dense, the eggs look more homogeneous and transparent than before salting. Another sign to stop stir-ring is when the eggs do not stick to the stirring paddle, but roll down it. For caviars heavily soiled with sand (e.g. flounder caviar) it is better to use brine salting.

Draining over small mesh size netting retards dewatering. Shaking of screens, centrifu-gation or applying vacuum may be necessary.

Generally both unsalted fresh or frozen and salted ovaries of ordinary fish can be util-ized for caviar processing.

Ordinary caviar of small size eggs of both ocean and freshwater fish are dry salted. Only larger size eggs of 2 mm and up are brine salted. Table 8-1 provides information on or-dinary fish ovaries. If ovaries are soft by nature or after defrosting, they are first brine salted in cold or hot brine to strengthen them and only then are they screened.

TABLE 8-1

ORDINARY FISH OVARIES

Ovaries with small size eggs and thick membranes may withstand preliminary washing with hot light brine. The use of 90°C light brine to wash off slime from pike ovaries be-fore screening has been reported.

Ordinary fish ovaries are often unusually coloured or contain discoloured degenerated eggs. They should be outgraded before screening. Unevenly coloured eggs in the caviar mass are recognisable even after dying. This makes a second grade product. Different but evenly coloured ovaries should be processed in separate lots. Different colour shades are typical for cod, halibut, sole, alewife, perch, sauger and carp ovaries. There is less difference in the colour shade of herring, pollack, capelin, pike and mullet ovaries.

The basic colour of all ordinary fish ovaries ranges from pale yellow to yellow-orange. Sometimes greenish and purplish shades appear. The egg membranes consist of many layers. The yolky interior fluid is quite viscous even before salting. This results in ordi-nary fish caviars being firm and not providing a juicy mouthfeel, rather being quite chewy. They contain less fat and hence less flavour. As with sturgeon and salmon cav-iars, only mature ovaries are fit for caviar processing. Care should be exercised in ex-tracting ovaries. Because of the smaller size of the fish, machine butchering takes place more often and bleeding is not performed. This may result in heavy contamination from the guts and bitterness as a result of damaging of the gall bladder. The same rule applies as with the 'noble fish' (sturgeon, salmon): after belly cutting, detach the ovaries first and immediately rinse them. The yield of screened eggs from mature ovaries of good quality is 80-85%.

In countries where legislative regulations allow, ordinary fish caviar is salted with a mix of 98.7% salt and 1.3% saltpetre (Potassium Nitrate).

It is typical for some ordinary fish caviars to have little flavour or sometimes a slightly bitter aftertaste. That is why flavouring of ordinary fish caviars with spices, onions, fish flavours and thickening agents is widely produced. Also sugar, sauces, and vegetable oils are used in much larger proportions than in salmonid caviar. The common defect of ordinary caviar is their rubbery texture. This may be the result of pasteurization or over-drying.

Figure 8-5 shows different types of ordinary fish caviar.

a) Flying fish b) Flying'fish dyed c) Flying fish with soya sauce d) White-fish e) Herring

Caviar can be smoked in conventional kilns using cold smoke. To compensate for the dryness, plenty of vegetable oil should be added before packing. Attempts to introduce smoked salmon and cod caviar products to the marketplace did not succeed. Whereas, smoked and smoke-dried whole ovaries are quite popular.

Canned and cooked products from screened ordinary fish eggs can hardly be called cav-iar products. They are popular in Europe. The technology for canned and cooked cod caviar is well established and described below.

Very fresh chilled or thawed frozen cod roe, either whole or broken are suitable. Separa-tion of membranes takes place when ovaries are passed through a low revolution mixer. The membranes remain wrapped around the shaft. The remaining debris is removed by conventional screening over a flat screen. Cans are filled with screened cod eggs, mixed with 15-25% water, 1-1.5% salt and 1-5% peanut oil. The final product, after 75 min-utes cooking at 120°C in a 10 oz. flat tin, has a slightly pink colour, is firm and slices easily. Equally popular in Europe are spreadable, pasteurized (at 70-80°C) pate type products blended with water, vegetable oil, spices, and packed in tubes. Only very fresh ovaries should be used for this product. Because both products are mixed or blended with water, draining after screening is not necessary.

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