FOREWORD

1.0 CAVIAR PRODUCTS
1.1 INTRODUCTION
1.2 THE WORD 'CAVIAR'
1.3 LABELLING PRODUCTS
1.4 CANADIAN ROE RESOURCES
2.0 ROE
2.1 OVARIES
2.2 MATURITY
2.3 YIELD
2.4 FROZEN ROE
2.5 GRADING FRESHNESS
2.6 CHEMICAL COMPOSITION
2.7 EGG STRUCTURE
3.0 SCREENING
3.1 SCREENING OPERATION
3.2 SCREENING TECHNIQUE
3.3 SCREENING DEVICES
3.4 MECHANIZED SCREENING
4.0 SALTING
4.1 PRESERVATIVE ACTION
4.2 THE SALTING MECHANISM
4.3 SALINITY
4.5 CURING EFFECT
4.6 SALTING TIME
4.7 SALINITY MEASUREMENTS
4.8 DRAINING, EGG VISCOSITY AND VISCOSITY MEASUREMENTS
5.0 PACKING
5.1 FREEZING AND REFRIGERATION
5.2 BULK AND RETAIL PACKAGE
5.3 PACKAGE TYPE
5.4 CHEMICAL PRESERVATION
5.5 ADDITIVES AND DYES
5.6 PASTEURIZATION
5.7 PACKAGING OVERVIEW
6.0 QUALITY AND SHELF-LIFE
6.1 QUALITY GRADING
6.2 ORGANOLEPTIC TRIALS
6.3 DEFECTS
6.4 CHEMICAL AND BACTERIOLOGICAL EXAMINATIONS
6.5 SHELF-LIFE
6.6 QUALITY CONTROL AND ASSURANCE
7.0 THE CAVIAR SHOP
7.1 LAYOUT AND MECHANIZATION
7.2 PLANNING A SALMON CAVIAR OPERATION
7.3 WATER QUALITY
7.4 SALT QUALITY
7.5 BRINE PROPERTIES
7.6 BRINE MAKING REQUIREMENTS AND APPARATUS
7.7 SALTING TANKS
7.8 MISCELLANEOUS TOOLS, INSTRUMENTS AND MECHANISMS
7.9 SANITATION
8.0 PROCESSING DIFFERENT SPECIES
8.1 HARVESTING LUMPFISH ROE
8.2 PROCESSING LUMPFISH CAVIAR
8.3 WHITEFISH AND OTHER ORDINARY FISH
8.4 STURGEON FISHERIES
8.5 PROCESSING STURGEON CAVIAR
8.6 SALMON FISHERIES
8.7 PROCESSING SALMON CAVIAR
8.8 ARTIFICIAL CAVIARS

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4.0 SALTING

Though chemical preservatives or pasteurization are used to enhance better shelflife of caviar, salt remains the main, and in the majority of cases, the only preservative used in processing caviar.

4.1 PRESERVATIVE ACTION

The action of salt in caviar processing manifests itself in suppressing the growth of bac-teria and also in killing them. However this action is only partially effective because of comparatively low salt concentrations in modem caviar products, namely 3.5 to 4%. Other reasons for the limited preservation effect is the nature of microorganisms com-monly present in caviar, i.e. their survivability and growth at the given salinities and pH range (4.3 to 5.9) typical for caviars.

As an example one could mention the yeast Torulopsis Candida frequently isolated from salt brines, pickled cucumber, marine plants, and fish and found in caviars. This organ-ism may grow at temperatures as low as 0°C and salt concentrations as high as 20%. At the same time it does not survive pasteurization at 60°C after 20 minutes. Poor quality salt may itself be the source of salt tolerant microorganisms, e.g. sun-dried, mined salts or salts improperly stored for a lengthy time.

The salt not only breaks down bacterial cells but also protects the proteins from the ad-verse action of enzymes.

4.2 THE SALTING MECHANISM

The salting mechanism of caviar is less understood than that of fish. Screened eggs, as opposed to fish or whole ovaries, have a much larger relative area exposed to the brine solution or to the natural brine generated while dry salting is applied. Also, the hydrophillic proteins in caviar are not intermixed with fat and various fibers which would resist the diffusion of salt from the brine. This diffusion through the semiperme-able outer shell of the egg is sometimes referred to as 'osmosis'. Another easy entryway for the brine is through the micropyle in the later maturity stages, i.e. the little hole in the outer membrane through which the egg is fertilized. Thus, caviar products are getting salted, i.e. salt concentrations are equalized in all aqueous phases of the system, very rapidly. In comparison, salt penetrates fish flesh at speeds of 0.5 to 1.5 mm per hour, whereas for singled out eggs this process may take less than a minute. This is the reason, why one should be extremely careful during the technological process to keep the eggs in contact with water or aqueous solutions only for short periods of time. Rinsing should be rapid, salting and desalting carefully moni-tored. An example of the changes in salt and moisture content of chum eggs during the salting process is shown on Figure 4-1.

Figure 4-1

Salinity and Moisture

While salting, the egg undergoes physical changes which results in the egg swelling, be-coming round, firm, elastic and gaining weight. This fact deserves special attention. While salting fish flesh in saturated brines we may loose weight because fish flesh is comprised of 80% water. Fish egg proteins are much less aqueous and the salting proc-ess results in substantial gains in weight. To illustrate this, one could mention the fact, that when a whole (not gutted) fish with roe is salted the roe tastes saltier than the flesh.

When the egg is first placed in brine slight shrinkage of the yolk sack occurs as some colloidal substances are extruded into the space between the outer membrane and the yolk sac (see Figure 2-5). Water and electrolytes (brine) are passing through the mem-brane pores in opposite directions, but the colloidal substances can't. They remain under the membrane and continue to absorb water until counteracted by the pressure of the membrane. The round shape of the egg is now stabilized. This phenomenon may be ob-served while salting, or, more often, round shape stabilization takes place after the salt-ing is finished and eggs are left to drain. That is why one should not be worried if the eggs do not have a round shape and look slightly shrunken and wet immediately after salting. The residue of brine remaining outside the eggs continue their passage through the shell and after 20 minutes to several hours the eggs look perfectly round.
It is known that good quality eggs which look somewhat shrunken and are vacuum packed immediately after salting and dewatering, recover to a perfectly round shape even inside the glass jars.

FIGURE 4-2: Floatation Principle

a) Whole and broken chum eggs
b) Use of agitation or air bubbling

When eggs are exposed to pure water or light brines during various lengthy technologi-cal steps, eggs become 'water' and loose their specific taste. In water or light brines eggs will usually sink and the lighter debris float, whereas in more saturated brines eggs will float. For salmon eggs this threshold is 60% saturated brine.

Figure 4-2 shows egg floatation properties in 100% and 60% saturated brines. The white specks are floating broken eggs. The principle is used in egg separating systems, see Figure 3-9. The use of warm brines and extensive exposure to water or light brines may create difficulties in monitoring the technological process. Use of cold saturated brines and very short-time washing-rinsing operations in water or light brines is prevailing in the industry.

Lumpfish, whitefish, herring and other smaller size roes are relatively stronger than salmon or sturgeon roes and withstand the rigor of washing procedures much better. A gentle stream of potable fresh water could steadily run over the roes as they are being rubbed. Also eggs which remain on the screens could be gently washed off with water. In processing whitefish caviar the flotation principle is recommended. Screened eggs are stirred in a water solution and the floating debris and broken egg skeins are decanted.

Although whenever possible floatation cleaning should be avoided it can be performed as a batch process or continually. However the later may be difficult to control and hence damaging to caviar quality. The egg - water ratio varies from 1:1 to 1:10 and washing continues until all extraneous material is removed and the salting operation can proceed. Screened salmon roe, could be quickly rinsed when necessary before final salting in 1-2% cold brine in order to wash off broken eggs and yolk. Even screened sturgeon roe is rinsed in cold water to get rid of extraneous mate-rial. However rinsing time does not exceed 30 seconds.

To summarize, the decision to use or not to use rinsing depends on the quality and cleanliness of the screened roe. If the ovaries were weak and the tools were not kept clean one is forced to employ rinsing. Instead of pure water it is always advisable to use cold light brine of slightly lower salinity than the salinity of the final product and keep the screened eggs in contact with the rinsing solution only for short times. Otherwise the product may become watery in taste and unfit for freezing or prolonged storage, because it tends to release excessive juice.

4.3 SALINITY

The existing trend of lowering sodium consumption for health reasons is effecting deci-sions on how caviar should be processed. It could be argued, that the way caviar is con-sumed and the negligible role of caviar in the overall human diet, caviar salinity is not a health issue at all. It is much more important to consider the potential well known Clos-tridium botulinum danger from marketing this noncooked or nonpasteurized fish prod-uct in vacuum packages.

The issue was investigated by injecting spores of Clostridium botulinum into bottled salmon and lumpfish caviars and subjecting them to abusive (+30°C) temperatures. The results of these experiments allow formulation of safety parameters which will prevent formation of toxins, see Table 4-1.

TABLE 4-1

MINIMUM CAVIAR SALINITIES
TO ASSURE PRODUCT SAFETY

Good manufacturing practice would be to produce caviars with salinities greater than 3.36%. This number takes into account possible changes of pH during storage. How-ever, processors are often faced with the market demand to keep salinities lower/ as lit-tle as 2% in extreme cases. This results in the need for frequent pH examinations and very strict limitations on storage time and temperature conditions. On the other hand there are limits for lowering salinity which may result in significant reduction of flavour and hence in consumer acceptability.

One should mention the opinion from the Seafood Products Research Center USFDA, Bothell, Washington (personnel communication) that caviar type products, as opposed to products prepared from whole ovaries, are less susceptible to contamination from bacteria and parasites. The reason is that after the eggs are singled out and cleaned of debris and connective tissue they are thoroughly washed off with brine by virtue of the very technology of the process.

The above mentioned salinity, 3.36%, provides for a well balanced effect of enhancing the taste characteristics expected from a 'good caviar' combined with moderate saltiness and pleasant viscosity, flavour and aroma strength typical for the specific fish, sweet-ness, fullness or thickness of mouthfeel. The later is caused by egg interior viscosity. Taking into account potential salinity measurement errors the overall caviar salinity tar-get should be 3.6%.

Salinity is also one of the factors affecting the final product viscosity. Experiments con-firm a very high correlation between these two factors for any comparable lots. An ex-ample for chum caviar is given in Figure 4-3.

Figure 4-3

Viscosity of Chum Caviar*

* cps - 'centipoise', the viscosity measurement unit

It is one of the challenges facing caviar processors to achieve reduced sodium while maintaining the flavour. There are two principle ways to achieve acceptable flavour in reduced sodium foods. One is to add flavours like lemon, vinegar, spices, or glycerol which mask the 'raw' taste of too lightly salted caviar. The other is to introduce non-sodium 'salty' ingredients like calcium or potassium chloride, or glutamic acid.
These additives are not used in sturgeon and salmonid caviars but are known to be used in cod, herring and pike caviars.

4.5 CURING EFFECT

It is through the curing process of raw (noncooked) fisheries products that they ripen, or as technologists would say they 'mature'/ to become the familiar delicacies, with the changed texture, with flavour homogeneity and specificity of the bouquet, which we consume. There is no further culinary interference and our pallet is used to recognize this specific taste. If the curing process is not complete our palate will judge the product as 'raw'. With caviar the curing takes place due to salt and certain time-temperature conditions after salting. The mechanisms of this process are still not fully understood.

The combined effect of several processes is believed to be responsible for the biochemical changes which result in curing: breakdown of proteins by proteolytic, and fats by lipolytic, enzymes, microbiological activity and fermentation.

Often caviar type dishes and appetizers are garnished with strongly flavoured condi-ments (onions, lemons). One should always suspect that such a presentation is driven by the desire to mask the 'raw' impression of improperly cured eggs or, even worse, the beginning of spoilage.

The maturation or curing, as well as the salting processes, in caviar proceed much faster than in flesh. The only way to monitor the curing is to provide a certain favourable tem-perature and time regime after salting. To overdo, means to hold the salted eggs before packaging and storing: a) for too long, b) at too high temperatures, or c) at too low temperatures. There are known cases of salmon caviar spoilage because of holding them 'for draining' for several days. At the same time one should not rush salmon caviar into the freezer within hours after salting. This won't provide for a 'good cure'. The curing process is not interrupted when caviar is vacuum packed in retail containers, immedi-ately after dewatering, provided it is left for a certain number of hours at temperatures around 12°-16°C. Higher curing room temperatures may trigger fat oxidation.

4.6 SALTING TIME

Salinity is by far the most important and easily detectable consumer index used to judge caviar quality. In the case of dry salted caviars, e.g. sturgeon or lumpfish caviars, salt is added to each batch as a % of screened egg weight. The challenge is to predict the salt uptake in view of the excessive natural brine originating during the dry salting and draining operations. This uptake depends on egg maturity, freshness, salting temperature, salting time and draining intensity. Recommendations on the amount of salt which has to be added in order to meet the desired salinity of the final product, are based on experience.

The task becomes more difficult with the trend to process low salinity products. As a rule of thumb, good quality sturgeon eggs should be mixed with 4.5 to 5% fine salt in order to obtain 3 to 3.5% salted caviar.

To provide reliable technological recommendations for brine salting, e.g. in salmon cav-iar processing, which will assure final product salinities of 3.5 - 3.8% is even more dif-ficult.

To evaluate objectively the influence on salinity of the combined effect of many con-tributing variable factors is impossible. Under- or oversalted lots appear frequently on the market. Changing caviar salinity by a secondary salting, or by trying to desalt caviar products, inevitably lowers caviar grade and can result in a nonmarketable product. Fi-nal salt content depends on various factors, the main factor being salting time. None of these factors affects the salinity linearly. To get precise recommendations in such a multi-related system with the required level of accuracy is very difficult. This is the rea-son why all the existing manuals and expert recommendations give a very wide range of brine salting times. The "black magic" behind these numbers is to know how to take into consideration the factors mentioned in Table 4-2.

TABLE 4-2

FACTORS AFFECTING SALMON EGG SALTING TIME IN BRINE

This is not the case with heavy salted products/ where precise salting times are not criti-cal. At salinities of 10% (e.g. salted salmon ovaries, 'Sujiko') the eggs are saturated and the salting process slows down considerably, hence fluctuations in salting time of sev-eral minutes do not affect the product salinity.

Practically, monitoring the desirable salinity under industrial conditions can be done with an accuracy of ±0.3%. This has to be taken into account in contract arrangements between processors and brokers. As an example, several experimental salting curves for Chum caviar are shown on Figure 4-4. These curves illustrate only the trend and cannot be used as salting guidelines. Previously frozen, or non-fresh eggs, absorb salt very quickly and salting is stopped before a desirable inner liquid viscosity is achieved. It is for this reason that only roe of the highest grades (not frozen and very fresh) can be processed into low salted caviar ('malosol')/ which has a pleasant, not watery viscosity.

Figure 4-4

Salting Curves

Evaluation of the freshness and maturity of the ovary is quite subjective, yet these fac-tors strongly affect the salting time. The influence of various factors on salting time in saturated brine which are needed to achieve a desired final product salinity, shown in Table 4-2, can only show the general trend without attaching any numerical value to de-fine that influence. The actual time of salting salmon eggs may vary from two to twenty minutes.

The only sure way to determine salting time for any particular batch, in order to achieve the desired caviar salinity with ±0.3% accuracy/ is to perform trial salting of a small sample and measure the actual salinity vs salting time. In practical terms this means, that every time the conditions described in Table 4-2 are changed trial salting should be performed. Even the most experienced experts can't accurately determine required salt-ing time by looking at the roe or by tasting while the salting process goes on. There are many known cases of over or undersalting of large batches when the method of trial batches was ignored.

The method consists of the following steps:

• Take a representative screened roe sample large enough for 5-6 salinity measure-ments by the chosen measuring method, say 300 grams.
• Using the same roe/brine ratio as planned for the main batch in consideration, start to agitate the roe.
• Every 2 minutes remove a small portion of roe, enough to measure salinity, and drain it off.
• Measure salinity of all samples taken and choose salting time according to the salin-ity vs. salting time curve.

Usually the procedure is repeated every 3-4 hours unless the conditions change earlier.
Any desalting of oversalted salmon eggs in a light brine results in 'watery' eggs, which become softer and release excessive juice during subsequent storage.
In the case of lumpfish caviar desalting is part of the technological process. In this case, in order to monitor the process similarly to the described salting curves in Figure 4-4, 'desalting' curves should be determined experimentally.

For undersalted eggs secondary brining is not damaging if performed without delay. Adding very fine dry salt in order to increase salinity to the desired level is done, but it may damage the eggs while mixing.

A special note should be made regarding salting in warm brines. Pressed sturgeon caviar which is processed from weak and immature roes is brine salted at temperatures over 40°C for 1.5 to 8 minutes, depending on all other factors, particularly on egg size. Salt-ing in warm brines brings up a distinctive, prized sturgeon flavour. Weak salmon ova-ries if salted at 30-40°C also yield a product which is milder in taste as compared with caviar salted at the usual 8-10°C brine temperature. The product stores better, i.e. with-out releasing excessive juice.

The effect of warm brine can be explained by partial denaturation and coagulation of proteins, which results in higher egg interior viscosity.

There is another situation for using warm brine. It is for caviar processed from previ-ously frozen ovaries extracted from frozen salmon. The ovaries are initially defrosted to -1°C in running water. After draining they are salted in saturated brine at 15°C for 6 minutes. The ovaries firm up. Then they are put into a 70% saturated brine at 35-40°C and gently stirred for 3-5 minutes until the eggs separate. Apparently the combined ef-fect of thermotreatment and previous freezing weakens and breaks up the connective tissue, so the eggs are simultaneously separated and salted. This 'wef caviar technology is sometimes used for home made salmon caviar. Eggs brined in warm brines drain faster.

4.7 SALINITY MEASUREMENTS

Any caviar salinity measuring method should be rapid, convenient and accurate within ±0.1 to ±0.3%. The popular Quantab Chloride Titrator method employs direct interac-tion of chloride with silver dichromate. For aqueous samples, up to 12% salt concentra-tion Quantab Chloride Titrators could be used directly without diluting the sample. For caviar salinity measurement the sample has to be prepared by blending a representative caviar portion with nine portions of water. Vigorous mixing will ensure extraction of salt. The solution is then filtered to get rid of egg membranes, and tissue particles. The lower end of the Quantab is placed into the solution. The reading is done after 10-12 minutes. This method is not convenient and its accuracy is low. It should be used only for rough checks on the final product.

The classical argentometric chemical method of checking salt content by titration with silver nitrate is costly and requires trained personnel.

Most popular are conductometric salt analyzers, which provide an instantaneous reading of salinity, usually on a digital display. The aqueous sample is placed into, or poured through, an electric measuring cell. The sample preparation remains the same as de-scribed above with Quantab titrators. By using any conventional electrical grinder to break up the eggs and extract the salt into the water the duration of this procedure is about 2 minutes per measurement, see Figure 4-5. The instrument should be calibrated according .to manufacturers instructions. The use of tap water to dilute samples, as op-posed to distilled water, usually does not affect measurement accuracy. After each measurement the measuring cell, and especially the measuring electrodes, should be rinsed.

FIGURE 4-5: Trial Salting

1) Salting
2) Taking samples every 2 minutes
3) Weighing an egg sample and adding water, 1:9
4) Blending
5) Filtering
6) Measuring

Finally, the use of chloride ion-selective electrodes can be recommended as an instant measuring technique which consists of smashing up of a representative sample inside a plastic bag and applying the chloride ion-selective electrode directly to the mixture of broken shells and fluid. Special experiments have proven, that there is no need to sepa-rate the broken skins and to apply the electrode to the drained off juice. The electrode should be held by its own weight (no special pressure) and turned back and forth until a stable reading is obtained. The time required for one reading is 15 to 45 seconds, see Figure 4-6.

FIGURE 4-6: Using Chloride Ion-selective Electrode

The readings could be taken by means of a pH meter. The pH meter has to be calibrated using standard solutions. Not all the instruments are designed to provide for direct read-ing of salt concentration, instead they will read millivolts. In this case salinity can be de-termined graphically using calibration curves. Special attention should be paid to keep the electrode working surface clean.

To conclude, the use of chloride ion-selective electrodes is advantageous in that the sample preparation does not require any weighing or filtration efforts. However, the sensitivity to instrument cleanliness, the need of frequent checking of the calibration curve and potential instrumental errors makes this method unattractive. The majority of processors prefer conductometric salt analyzers.

4.8 DRAINING, EGG VISCOSITY AND VISCOSITY MEASUREMENTS

Draining after salting is a technological procedure which may contribute to caviar qual-ity. The term 'draining' in this context will mean the combined effect of dewatering and air drying. 'Good quality' caviar eggs hold their round shape, are moist and shiny, do not burst easily, do not stick in lumps. These 'good quality' properties vary depending on caviar type by species or ethnic taste traditions. The caviar properties mentioned above describe the exterior mechanical properties of the bulk of the eggs, which influences our visual perception of good quality. Even more important are egg interior rheological properties - the viscosity of inner yolk fluid. Apart from good taste we expect good salmon and sturgeon caviar not be too chewy, which means the egg should 'melf in the mouth and the inner yolky fluid should have a pleasant viscosity. All these caviar properties depend greatly on egg freshness, maturity and draining regimes. At the same time other traditional perceptions of 'good quality' like, 'popiness' could influence the technological decisions the processor has to make.

Dewatering and drying techniques which constitute draining could be more or less in-tensive and last for minutes up to 24 hours.

There are many practical ways to regulate, to a certain extent, egg rheological properties before they are packed and stored. The commonly used draining procedure is to put salted eggs over a screen or into draining baskets and allow the excess liquid to drain off.

Sturgeon eggs are put onto sieves (screens) in 3 to 4 cm layers for only 5-10 minutes. When packed into retail packages they should remain quite moist so they could easily flow through the bin and volume measuring device of the filling machines. It is known that when overdried bulk packages of the salmon caviar are repacked into retail contain-ers using filling machines some light brine is added into the bin to assist the flow and avoid egg breakage.

When sturgeon eggs are packed into institutional size (1.8 kg) cans eggs are drained to a larger extent. After draining over screens the caviar is manually filled into cans, which are put on their side for up to two hours. Excess liquid drains off through the clearance along the seams of the lid and can body (See Figure 4-7a). Finally, the cans are stacked into columns of 3-4 cans and subjected to pressure by putting measured weights on the top for hours. The excess liquid continues to drain along the perimeter of the lid. The lid slips down 2-3 mm short of the prominent body lug and all the air cavities inside the product disappear. Another solution is to use a manual screw press, gradually increasing pressure.

FIGURE 4-7: Draining

a) Sturgeon caviar, Guryev, Russia
b) Salmon caviar, Canada
c) Salmon caviar, Japan

Draining of salmon caviar after salting is done in plastic baskets with appropriate size openings. Elongated openings are preferable. Synthetic soft mesh material basket liners are very convenient for handling eggs, in baskets with oversized openings (Figure 4-8).

FIGURE 4-8: Using Synthetic Liners

FIGURE 4-9: Honey Like Viscous Droplet

Some processors use traditional bamboo baskets, for draining (Figure 4-7c). However, soon after the excess brine runs off the tiny clearances between the bamboo strips clog and draining, in fact, stops. Further dewatering takes place only through moisture evaporation from the surface. The top egg layer may overdry and the eggs shrink, fade and become hard. At the same time the bottom layers, being sealed off from the outside, remain very moist. Before packing, the eggs from several baskets are dumped together into containers for further technological steps. The dry and moist eggs intermix, and the dry eggs regain their shape, colour and consistency by absorbing the available moisture. The lot homogenicity recovers.

The described partial overdrying process is difficult to monitor. The overdrying rate de-pends on the exposed egg surface to volume ratio, on the room temperature and mois-ture, on the air circulation speed. In a noncontrolled atmosphere or on rainy days a salmon egg layer over 8 cm may 'drain' for days and the inside will still remain moist creating favourable conditions for spoilage.

Another danger of lengthy draining is through exposure to airborne bacteria. That is why the traditional draining methods are now replaced by intensive modern dewatering technological operations which allow processors to shorten the 'overnight draining' batch process. Modern online dewatering technology provides for an uninterrupted salt-ing-draining-packing process.

Because of the fragile nature and value of sturgeon caviar the above described tradi-tional draining methods will never change. For salmon eggs several modem means of enhanced dewatering can be mentioned: running salted eggs through a clean screening device (this will also recapture broken egg membranes), centrifugation of salted eggs in a perforated basket, running salted eggs through a perforated drum or a perforated con-veyor belt and forced blowing of clean air of controlled temperature and dryness. Dry-ing by air blowing has to be very carefully monitored because overdried eggs are very difficult to reconstitute.

Draining off small size egg caviars like lumpfish, whitefish, herring, flyfish may create problems because of the small size of the draining mesh, which clogs very quickly. An improvement to this passive draining method consists of holding the batch over a vac-uum chamber and thus enhancing the drip uptake.

The exterior characteristics of the bulk of the eggs affected by draining are excessive juice on the bottom of the container and excessive fluidity of the egg bulk or, excessive dryness and lumping. These visually judged quality indices could be improved by quick rinsing and secondary draining, adding vegetable oils or glycerol which helps to pre-serve the shiny and bright appearance, prevents sticking and make the eggs 'rattle like peas' when eggs are turned in a bowl.

Egg interior rheological properties, i.e. the viscosity of inner fluid is a major quality in-dex, especially for salmon caviar.

The best salmon egg caviar is described as having 'honey like' viscosity. The traditional way to check the 'right' salmon egg viscosity is to squeeze a single egg between the fin-gers, or over glass. The egg is not supposed to burst easily. When it finally collapses the inner liquid does not spurt like a water jet, but remains like a viscous droplet. Obvi-ously, the described criteria is very subjective and efforts have been made to employ in-strumental measurement methods of both egg strength to rupture and inner fluid viscos-ity.

Many factors influence final egg inner fluid viscosity. It changes during caviar shelflife and depends on the packing options, e.g. minimal viscosity changes are expected in vacuum packed containers. The upper layer of salmon caviar packed in airtight plastic pails dries up, turns chewy and looks whitish. At frozen storage the lay-ers exposed to air show a typical 'caviar freeze burn'.

Factors which influence salmon egg inner fluid viscosity are: salinity, final moisture content as a result of dewatering intensity, brine temperature during salting, pasteuriza-tion, freshness of eggs used to make caviar.

Using laboratory viscometers it is possible to obtain an objective judgement on egg inte-rior liquid viscosity. Figure 4-10. A representative interior liquid sample is obtained by smashing and straining an egg portion, centrifugation of this fluid to remove immiscible liquid material and separation of the higher density protein layers, which forms the ma-jor part of the fluid. The separated protein fraction is then placed into the cup of a Brookfield Microviscometer. The measured apparent viscosity is used as a relative ob-jective viscosity index. Measurements of shear rates are recorded at a range of rotor revolutions: 5 to 200 r.p.m. In spite of all the inaccuracies of the method (±6%), it pro-vides one with an objective tool to judge relative numerical viscosity changes depending on different technological regimes.

FIGURE 4-10: Viscosity Measurements

a) Obtaining interior liquid
b) Isolation of the higher density portion
c) Measurement
d) Equipment and tools

The apparent viscosity unit is 'poise" (ps) or 'centipoise' (cps), where of 1 ps=100 cps. Viscosity is defined as the ratio between shear stress and shear rate as measured by the viscometer. If this ratio is constant we call the behaviour of such substances Newtonian flow. The rheological nature of the inner egg liquid from both fresh and processed salmon eggs was proven to be Newtonian.

The affect of salinity on viscosity is given on Figure 4-3 for chum caviar.
One of the main obstacles to processing caviar from frozen eggs is the resulting low vis-cosity. Frozen chum eggs have a low starting viscosity of 170 cps as opposed to 400 cps for refrigerated eggs.

There is a strong correlation between caviar viscosity and moisture. Using different draining-drying temperatures and, air blowing velocities, caviar viscosity can be easily manipulated. However, at excessively intensive regimes egg shape and viscosity can irreversibly deteriorate.

Attempts to alter chum caviar inner fluid viscosity by adding thickening agents failed. Apparently, the long chain molecules of the thickening agents do not penetrate egg membranes. Such a treatment may only affect the exterior viscosity (fluidity) of the bulk of the eggs.

In summary, forced draining - drying by cold air blowing is an acceptable principle as it can shorten the duration of this operation and also increase the viscosity of the caviar processed from frozen roe. Overnight draining has to be done under very high sanitation standards. Overdrained (too viscous) caviar can not be corrected. The required draining time depends on egg maturity, air temperature, egg layer height, air exchange rate (blower), initial moisture content of eggs which is in turn affected by freshness and whether or not the ovaries were frozen. In the plants, salmon caviar is packed after 30 minutes and up to 12 hours of draining.

The "right" level of viscosity can be determined only organoleptically. Taste panels were specifically assigned to assess this. As a result, the thresholds of non-acceptable "too liquid" and "too viscous" chum caviar were found. 400-1,500 cps was considered as good quality. More viscous caviar appeals to Japanese, less viscous caviar is favoured by the Europeans. The significantly unacceptable caviar samples were always at the ex-tremes of less than 200 and over 2,500 cps.

Table 4-3 show some of the taste panel results. The preference was evaluated by a 9 point system where "like extremely" was given 9 and "dislike extremely" was given 1. All the samples were prepared from the same fresh lot of salmon.

TABLE 4-3

SALMON CAVIAR
VISCOSITY: ORGANOLEPTIC TESTS
(12 EXPERTS)

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