How do you make caviar?
Caviar comes from a sturgeon and is, quite literally, the eggs that the sturgeon produces. From there, the rest of the process from farming and harvesting to handling are carried out by our team, and those processes make all the difference in the end product.
There are actually a range of different sturgeon roe from the Caspian Sea that can produce caviar. But the process of harvesting is done in one of only two different ways. After harvesting the process is actually relatively simple. The roe is simply rubbed over a mesh screen to separate out the membrane of the sack from the eggs themselves. Then, they are rinsed off and must be inspected individually. In fact, each egg is inspected with tweezers that allow broken eggs to be removed as well as any impurities or any residue from the membrane. Then, it can all be weighed out to exact specifications, salted, and packaged for consumption.
The production process, as mentioned, is relatively simple. But there are two different ways that the caviar can actually be harvested, and we’re going to take a look at what those are and just how they work so you can feel more prepared.
Understanding caviar processing is basic to understanding quality, shelf life and other aspects of the use of caviar. In this article, describe the basic processes used for the production caviar products, with comments about variations used in producing high quality caviar from particular species. Variations are also determined by the maturity and freshness of the eggs when they reach the processing plant. Some popular publications refer to caviar processing knowledge as an art form. We maintain that caviar processing is simple and the scientific issues underlying the technology are clear.
No matter which species is used, caviar always consists of detached, lightly salted, uncooked fish eggs. That is why many technological requirements, quality assessment methods and storage requirements are the same for different types of caviar.
However, processing caviar requires creativity. Differences in roe quality and in the biological properties of different species necessitate adjustments to processing techniques in order to produce the best possible quality and yield.
The material in this article summarizes international experience in processing all existing types of caviar. Readers wishing for more detailed information on processing caviar should refer to the comprehensive Roe Processing Manual by V. Sternin, 1991. A concise, step by step overview of processing different types of caviar is given in the Annex to this book, which also contains many useful and informative pictures illustrating the procedures, equipment and packaging.
Ovaries and eggs
The roes or ovaries of a fish consist of a single binary organ located symmetrically to the spinal column in the belly cavity. The ovaries are shaped like flattened tubes, narrowing towards the rear. Color varies from species and changes slightly as the fish matures. Color may also vary with the fish’s feed and there are differences among individuals. In extreme cases, albino salmon eggs have been reported, as have golden (instead of gray or black) sturgeon eggs. Color may also change as a dead fish gets stale. Nevertheless, color of the eggs from particular species is remarkably consistent most of the time. Sockeye eggs are bright reddish orange; chum salmon eggs are pale red with orange overtones; pink salmon eggs are pinkish-orange; most species of sturgeon eggs are blackish or brownish.
The outer skin or epithelium of the ovary is a dense, semitransparent and rather elastic film. Within this covering, the eggs are attached to connective tissue which envelops the eggs and is attached to the epithelium. Ovaries of some species, such as sturgeon and herring, form distinctive portions called lobes. Ovaries of other species, such as salmon and lumpfish, do not form lobes. As the ovaries mature, the connective tissue and the epithelium lose fatty materials, get thinner, weaken and, by the time the fish is ready to expel its eggs, almost disappear. Descriptions of the various maturity stages of salmon ovaries are given in table 4.1. (Note that these descriptions may be applicable to certain species, but not to others. Table 4.1 is intended for use only with salmonid species.)
An important aspect of caviar processing depends on the strength of the attachment of the eggs to the connective tissue. The eggs cannot be separated effectively unless the ovary is sufficiently mature, so that the connection is weak. Immature roes, with strong connection between eggs and tissue, are used for other products, where it is not necessary to separate the eggs. Immature roes may be used for non-granular pressed roe products (called yastikovaya ikra in Russian). Salmon roes are made into sujiko, a salted, non-granular, whole product, popular in Japan.
Salmon ovaries are most valuable for caviar production when they are at stage IV (see table 4.1). Salmon eggs at stage V have membranes which are too thick. However, there are no clear boundaries between the stages; some eggs from stage III and some from stage V may be processed successfully into good quality caviar.
Table 1.1. Ovary maturity stages for salmonids
I Immature. The ovaries look like narrow and flat yellowish vessel. Eggs are absent
II Ovaries are small in size. Eggs are discernable
III Ovaries occupy 50 percent of the belly cavity. Eggs are clearly recognizable, small in size, deeply colored, enveloped in connective tissue with considerable fatty deposits. Single eggs are difficult to detach.
IV Ovaries occupy almost the whole belly cavity, and can be torn apart only with some effort. Single eggs are easily detachable. Eggs are large in size except for the ones located at the rear end which may be smaller. Eggs remain opaque, the shape is not fully round and the egg outer shell is thin. Eggs burst when squeezed
V Ovaries very large. Fish belly shape typically round (“gravid”). Eggs very large in size throughout the ovaries. Eggs are partially or fully translucent and fully round. Eggs do not burst easily; their outer shell is elastic and thick. The connective tissue is very thin and weak with no fatty deposits. Single eggs are very easily detached when lightly rubbed over a screen. Eggs may “run” through genital pores when fish belly is squeezed
VI Ovaries occupy only part of the belly cav-ity. Connective tissue is shrunken. Several translucent eggs remain slightly attached-fish already spawned
As the ovaries mature, the eggs become a greater percentage of the weight of the ovary and of the fish itself. In some species, the eggs may constitute as much as 34 percent of body weight. Table 4.2 shows data for a number of different species. Pink salmon mature
Table 4.2 Ovary weight of various fish species
FISH Minimum Maximum Average
Chum 3-8 10-20 8-13
Pink 3-10 11-23 7-11
Coho 4-8 12-20 7-12
Chinook 1.5 19 10
Sockeye 3-5 11-15 6-8
Sturgeon 14 34 20
Herring 9 25 18
Pollock (Pacific) 4 25 14
Mackerel 5 7 6
Carp 6 20 16
Whitefish 6 17 14
Lumpfish 20 29 23
at the age of two, chums at three or four. Almost all Pacific salmon mature only once; they die after spawning. Sturgeon mature for the first time after five to 20 years, depending on species (see Article Two), but sturgeon mature a number of times during their lives. Older fish contain many more eggs than younger ones.
Management of salmon fisheries seldom takes account of roe maturity. It is designed specifically for stock conservation and enhancement. Chum roe, for example, is less valued at the beginning of the season (maturity III) and falls greatly in value towards the end of the season, when the egg membrane gets too thick (maturity V). The fishing regulations for sturgeon do take account of roe maturity, since the eggs are a major purpose of the harvest of these fish.
Roes are best when taken from live fish. In traditional sturgeon fisheries, the fish are delivered alive to the processing locations, where they may be held for several days before they are butchered. This has the additional advantage that it allows the digestive tract to cleanse itself, removing any possibility of contaminating the eggs with unpleasant tastes from the guts. Lumpfish are generally taken alive from the gillnets and the roses extracted immediately.
Salmon is mostly dead when landed, but roes should be removed before the onset of rigor mortis and the beginning of enzymatic processes which decompose the tissues. In general, roe extracted within 10 hours of catch is of high quality. Salmon held at freezing point in ice for up to 36 hours can also provide good quality material. If immediate processing is not impossible, it is better to remove the roes and hold them on ice than to leave them in the iced fish. Note that roes should not be in direct contact with ice, but should be placed in sealed containers buried in ice. Roes held inside fish deteriorate faster than extracted roes. Tables 4.3 and 4.4 indicate the drastic effects of different holding temperatures and methods on caviar quality and yield.
Table 4.4. Pink salmon ovaries: quality deterioration effects
Percentage of ovaries
Holding conditions over 12 hours Graded
N ͦ 1 Graded
N ͦ 2 Unit for caviar
Fish held with refrigeration 30 50 20
Fish held on ice at fishice ratio 3:1 64 33 3
Ovaries extracted and kept at 0 ͦ C 96 4 0
Source: Kizevetter, 1958.
For Pacific salmon, 95 percent or more of the roes, extracted before or during rigor mortis may be of the highest quality. The percentage of top quality roes drops to 75 once autolysis (enzymatic decomposition) begins. Similar figures apply to most other species used for caviar.
In practice, deliveries to the processing plant usually contain fish caught at different times under different conditions. The fish in a batch may not all have been iced and handles in exactly the same way. The processor must assess and grade each pair of ovaries individually to ensure consistent quality of product.
Farmed fish offer opportunities for producing roe from live fish. It has already been noted (see Article Two) that in the future sturgeon will be harvested several times by Caesarean section. However, it is unlikely that salmon farmers will want to keep their fish to sexual maturity since this is expensive in time and feed.
Careful quality grading of ovaries has an important bearing on the quality of the final caviar product as well as of the yields and profitability of the producer. Each ovary must be examined individually. In some cases, it may be possible to utilize part of an ovary for caviar, rejecting, say, the rear end which may contain smaller eggs or eggs which have not developed properly. In such cases, the ovary can be torn apart and the better piece utilized.
Grading has to take account of maturity (see table 4.1) and freshness (see table 4.5). Grading has to be done by eye by experienced personnel. At this time, it is not feasible to use objective instrumental or chemical tests to determine freshness and grade.
Table 4.5 shows freshness indicators for chum salmon ovaries, related also to the condition of the fish. As the fish deteriorates, so do the ovaries and the eggs. However, ovaries should be judged on their own merits, since it is sometimes possible to obtain good roe from fish that is less than top quality. Similar indicators to those in table 4.5 can be applied to most fish used for caviar.
As can be seen from the table, the requirements for top quality eggs are that they should be firm. When the eggs are squeezed they change shape but do not break, unless considerable pressure is used. Softer eggs, which are more sticky, give lesser quality caviar. Softer eggs may not be perfectly round and are easy to squeeze out of shape. The best quality eggs are obtained from the freshest fish.
Ovaries or eggs held without refrigeration before salting lose quality rapidly (figure 4.1). Noticeable changes can be observed in less than two hours. The eggs get softer and it is easier to break them. Breaking becomes easier as the eggs deteriorate further.
Table 4.5. Chum salmon ovaries: grading for freshness
Fish status Ovaries Eggs Caviar
Alive or very fresh. During or after rigor mortis (stiffering). No signs of autolysis. Convex eye. Transparent slime
Firm and elastic flesh
Gills bright and reddish
Fresh odor or oderless Light orange color, opaque or slightly transparent.
Shiny clean ovary surface.
Firm and elastic
Fresh odor or odorless Firm.
Can be crushed only under considerable pressure.
When squeezed eggs deform, but do not break Best caviar.
Fresh. Signs of autolysis. Flat eyes
Gills somewhat discoloured.
Slight malty odor Orange-reddish color.
No objectionable odors Soft eggs, easy to deform.
Break when squeezed, stick slightly together.
Round shape, slightly deformed Grade No. 1 caviar
Further deterioration, however, still considered fit for fresh/frozen products.
Gills increasingly discoloured
Off odors. Red color
.Flabby and soft ovaries Slimy and dull ovary surface
Slight off odors Soft eggs, easy to deform
Break when squeezed, stick slightly together Round shape, slightly deformed. Ovaries should be sorted out in two grades for processing:
Grade no. 1 & Grade No. 2 caviar.
Low grade salmon. Unfit for fresh/frozen products
Gills greenish and brownish. Very soft flesh
Strong off odors
Dark red color.
Soft, sticky and very slimy ovaries.
Unpleasant odors. Very soft.
Shape collapses under ovary weight. Burst when slightly squeezed.
Eggs are dull, and covered with vicous sticky slime.
Eggs stuck together. Ovaries unfit for caviar
Source: V. Sternin, 1982 and 1991
Broken eggs release a whitish juice. Decomposed eggs develop a sour smell. Old ovaries may become semi-liquid and give off sharp, unpleasant odors.
Figure 4.1. Grading chum salmon ovaries by freshness. L to R: Best —orange-red, firm, elastic. Second — reddish-orange, slightly soft. Poor — dark red. soft, slimy ovaries.
The higher the ambient temperature in which ovaries are stored, the faster the spoilage processes occur. Spoilage is a result of both enzymatic and microbiological action. Enzymes, which are natural substances contained in the live animal tissues, break down proteins and fats, a process known as autolysis. Enzymes act first on the outer membrane of the eggs, which softens. The egg shape deforms and the eggs may break easily during the separating process (screening), resulting in heavy losses of raw material for the processor. Ovaries must be chilled and may also be salted before screening to minimize losses. It is always advisable to process the ovaries as soon as possible for best quality and maximum yield.
Note that whole ovaries taken from a live fish are sterile, but they pick up bacteria and other microorganisms from the environment, from tools and working surfaces, or by contact with or leakage from the intestines of the fish. Good manufacturing practice for caviar requires the protection of the ovaries from such contamination, excellent sanitation and minimum time before processing. One objective of grading of ovaries is to separate raw material that will produce top quality caviar from inferior raw material. Only the best quality roes can be used for pasteurized caviar, since the pasteurization process may cause weak eggs to collapse in the container, giving a product with excessive juice and unpleasant odors.
Some authorities state that ovaries more than 6 or 7 hours after capture should not be used for caviar, as they become sticky and lose their shape. These are extremely strict recommendations, which are sometimes difficult to adhere to. It is not practical to lay down such rules; it is most important to judge each ovary on its merits.
The fish should be washed before the belly is cut. Then the ovaries should be detached and placed in a sanitary place before the viscera are removed. If the ovaries are removed with the viscera, the chances of contaminating the ovaries are much higher. The effects of such initial contamination cannot be reversed later.
The ovaries are then washed in cold water or a light brine of two to three percent salt. Slime is removed more easily with brine than with fresh water.
The use of frozen ovaries for caviar is unusual and the issues involved in its potential use are confusing. Ovaries containing delicate eggs cannot be frozen, because the eggs rupture when thawed. Russian standards do not permit sturgeon caviar to be made from frozen roe. However, sometimes ovaries can only be delivered to the processor in a frozen state and if these materials are to be utilized then technologists must find ways to process them.
Iranian standards permit dry-salted and brined caviar products to be made from frozen roes of cod, sablefish, herring and other species. Work on using frozen salmon roe is still in experimental stages in British Columbia and Alaska. Roes from chinooks caught by trollers with freezing capacity are commonly dumped with the viscera, although this material may have use for caviar.
When freezing roes, it is recommended that a fairly slow process be used: one that takes about 30 to 40 minutes to pass through the critical temperature zone of 0 to -5° C (32 to 23°F). It is also possible to use ovaries extracted from fish that was originally frozen whole.
This is standard technology for the roe herring industry of the Pacific coast of North America, although the herring roes are used for products where the eggs are not separated, but remain in the ovarian sac.
Frozen roe is thawed to -1° C (30°F) before screening. Over mature salmon eggs and small eggs with strong membranes from ordinary fish withstand freezing best. Thawed eggs require much less salting time than fresh eggs — sometimes as little as 30 to 60 seconds. Yields from frozen roes are lower than from comparable fresh roes. Yields decline the longer the roes are kept in frozen storage. Experiments with salmon indicate yields of 75 percent after screening and 60 percent for the final product from frozen salmon ovaries stored for up to 10 days. If the roes are kept for 20 to 25 days, yields fall to 60 percent and 30 percent respectively.
Caviar made from frozen ovaries is normally graded as a second quality product.
The interior viscosity of caviar made from frozen roe is lower, but organoleptic tests comparing salmon and other caviars made from fresh and frozen roes showed only small preferences for caviar made from fresh ovaries. Note that the shelf life of caviar made from frozen material is much shorter.
Size, color, shape, toughness and taste of fish eggs depend on species. The morphology of fish eggs is generally similar: each egg is a pigmented, semi-viscous, yolky emulsion encased in a membrane. The emulsion contains fatty globules of varying sizes and is called a colloidal solution. Within this solution there is a barely visible germinal vesicle.
The outer membrane of the egg is porous and it varies in strength, thickness and number of layers. Mature eggs contain an opening, called the micropyle, through which the spermatozoa enters to fertilize the egg. The colloidal interior – the yolk – is contained in its own membrane: there is some space (perivitelline space) between this membrane and the outer membrane. During salting this space absorbs brine. It swells and the egg becomes truly round and firm.
Figure 4.2 shows a salmon egg as an example of egg structure. Both outer and yolk membranes are porous and have microscopic channels which provide for egg metabolism while it is growing. Close to the yolk membrane are concentrated small size color fatty droplets, called lipochromes, which are responsible for the particular color shade of each egg.
Table 4.6. Fecundity and egg sizes
Fish Fecundity in thousands Egg diameter, mm
Sturgeon 5 to 6,000 Large – Over 2.5
Medium – 2.2 to 2.5
Small – ˂2.2
Pacific salmon 1.5 to 5 Chum – 4 to 5
Pink – 3.5 to 4
Coho – 3.5 to 4
Chinook – 6 to 7
Sockeye – 4 to 4.5
80 to 120
0.9 to 1.2
Flounder 90 to 1,600 0.8 to 1.2
Mackerel 200 to 450 0.8 to 1.0
Cod 2,500 to 10,000 0.3 to 0.8
Carp 200 to 1,000 0..8 to 1.6
Pike 10 to 210 2.5 to 2.8
Whitefish 50 to 150 0.9 to 1.4
Egg sizes vary greatly as indicated in table 4.6. Only sturgeon eggs, because of their great value, are normally size graded. These are classified into three size ranges, as shown in the table. Eggs from other fish are normally processed together as they come, without size grading.
Color. While the eggs from a single fish are all the same color, tints vary between fish of the same species. Sturgeon eggs are particularly variable. They can be shades of gray from light to dark, black, yellowish gray, brownish gray, greenish gray and even a dark golden color. Salmon eggs range from light orange through reddish orange to red. Most eggs from other fish are pale shades of gray, yellow, pink, green or brown. The majority of lumpfish eggs are pinkish, but sometimes the color ranges to purple and brown.
Mature eggs look brighter and shinier than immature eggs, which tend to be dull and opaque.
Toughness is usually judged by squeezing an egg until it breaks. Weakness indicates immaturity, staleness, that the egg was once frozen, or a combination of these factors. Testing by squeezing works with larger eggs, such as those from salmon and sturgeon. Smaller eggs, such as those from herring or carp, often have relatively stronger outer membranes, so the result of the squeezing is harder to evaluate.
Taste is typical of each species, although it may be affected somewhat by the fish’s feed and the water conditions in which it lived. Some sturgeon eggs may have a grassy or muddy aftertaste. Some salmon eggs, especially those of sockeye and coho, sometimes have a slightly bitter flavor. Pink salmon eggs are sweet. Numerous off-tastes occur in eggs of freshwater fish from pollutants. Some-times, undesirable flavors disappear when the eggs are salted; or, at least, they are masked by the salt.
What makes caviar different from other roe products is that the eggs are separated from the ovary and the tissue which contains and joins them. The process for separating the eggs is called screening. The most commonly used method is manual screening. The more valuable the roe, the more likely it is to be screened manually rather than mechanically. Manual processing minimizes losses of eggs during screening. A skilled operator can screen between 100 and 200 kilograms (roughly 200 to 400 pounds) of salmon roe an hour. Screening takes only a small part of the total time and labor required for producing caviar. Mechanized screening is mainly applicable when landings are very large in a short period, as may be the case on board a factory vessel, for example, or if the value of the roe is low, as with some ordinary fish.
Ovaries are rinsed and drained, then inspected to make sure they are free of blood clots, debris or other adulterants. They are then pressed through a screen made of wire mesh or other material. The operator uses a gentle, circular motion so that the eggs are pushed through the screen, while the connective tissues remain on top. Overly harsh handling of weak eggs results in excessive breakage. In this case, the eggs release an interior liquid and the broken egg becomes a whitish, empty membrane, which later is difficult to remove from the screen. A simple representation of the screening process is shown in figure 4.3.
Table 4.7. Screen mesh openings (mm)
Sturgeon Chum Coho and pink Whitefish Lumpfish Herring
Type of Screen Netting Netting. Metal sheet only for mechanized screening Netting or metal sheet Netting or metal sheet Metal sheet
Opening (mm) 6-8 10-12 7-9 6-7 5 2.5-3
*For salmon screening devices, the second screen opening is 5-6 mm and the slope screen opening are 2-3 mm square of 2-3 by 8-10 mm rectangular mesh.
Screens are made from stainless steel wire mesh, or perforated sheet metal. They can also be made from monofilament or multiple nylon twines. Historically, screens were made of braided cotton twines stretched on wooden frames, but these do not comply with modern food industry sanitation standards; however, such screens are still in use. Screens must be stretched flat and some designs include devices for maintaining the tension of the screen mesh. Table 4.7 shows mesh sizes used for certain fish roes.
Sturgeon roes are separated through a single screen. Salmon roes break more easily and produce more debris; they are usually out through a triple screen device. The eggs are passed through the top screen by the operators. The second screen, mounted 15 to 20 centimeters (about 9 inches) below, is designed to catch debris and clumps of eggs that fall through the top screen. The third screen is mounted at an angle so that the eggs roll down it, losing excessive fluid from broken the eggs and broken egg membranes. This screen is often quite long, as the further the eggs roll, the cleaner and dryer they will be. A typical salmon roe screen is illustrated in the Annex (see figure A7).
A machine with a vertical shaft is used in Russia for pollock and cod roes. Ovaries are delivered from a bin on to a horizontal, round stainless steel screen and are pushed through by six adjustable rubber blades on a shaft rotating at 40 to 50 rpm. The eggs fall through two more screens and then roll down a sloping screen. Output is said to be 900 kilos an hour for capelin and 350 kilos an hour for salmon eggs, with average yields of 88 percent and 75 percent respectively.
Lumpfish roes are normally screened mechanically in Canada, Iceland and the other major producing countries. These machines use horizontal shafts. The blades push the eggs through the perforated drum and are collected fopr further processing, while the debris is pushed to the end of the drum and removed through an opening.
Broken eggs and debris. Broken eggs, pieces of connective tissue and clumps of unseparated eggs are the major problems of the screening process, especially when screening salmon eggs. Eggs broken during screening are difficult to remove. The screens clog and screened eggs get soiled with broken membranes. Screens must be replaced and cleaned frequently. Debris from connective tissue and other unwanted material must be picked out from the screens by hand using vacuum suction. If rinsing operations takes place, debris and broken membranes can be made to float in light brine while the eggs sink to the vessel bottom. Finally, broken eggs can still be removed individually on an inspection line or during packing, using tweezers.
Eggs break less if they are kept cold, at about 3° to 5°C. Ovaries may be cooled by rinsing in cold light brine, although it is obviously preferable that they be kept cold at all times. Cooling the ovaries before screening does not improve quality but does increase the yield of whole eggs. Weak ovaries can be strengthened by salting in saturated brine for a short time before screening. This also increases the yield of whole eggs. It is advisable to tear apart ovaries before screening, so that the inner lobes are facing the screen, leaving the outer film on top.
Screened salmon eggs from fresh ovaries are almost perfectly round. They are translucent and have a shiny surface. They will roll easily on a sloping surface. The eggs from stale ovaries are sticky and do not roll down an incline, but slide. Screened eggs of all fish species should be clean, free of debris and broken eggs.
Egg separating system. Figure 4.4 shows schematically a salmon roe processing system, which could utilize either pure brine solutions or brine solutions containing enzymes. Such technologies do not employ the screening procedure discussed above and are better described as fish egg separating systems.
The use of enzymes to decompose connective tissues of salmon and trout ovaries has been known since the end of the 1960s. The technology aims to utilize less mature ovaries to provide yields higher than when manual screening is used. Proponents also claim lower labor costs. Although it is claimed that the enzyme solution only decomposes the connective tissues and does not affect the eggs itself, very thorough washing of screened eggs exposed to the enzyme action is required. The source of the enzymes is usually plant protease, or protease of animal origin. Treatment time is from several minutes to half an hour. The enzyme concentration in solution ranges between 0.02 and 0.1 percent. The process is reported to be used for making caviar from farmed trout. There is no information on the shelf life of caviar produced in enzyme separating systems. Prolonged contact of the eggs with watery solutions during the process makes the caviar taste watery. Egg separation systems are not popular.
Figure 4.4b. Photo shows the eggs leaving tank (4) in figure 4.4a.
Salt is the prime, in some cases the only, preservative used for caviar. Other means of preservation include the use of chemicals and pasteurization, but salting is the most important method used. Salt determines the viscosity of the inner fluids of the egg, an important quality feature in all caviars. The relationship between salinity and viscosity of chum salmon caviar is shown in figure 4.5.
Action of salt. Salt suppresses the growth of bacteria and kills bacteria. Salt also reduces the action of enzymes. Bacteria cause spoilage and may be harmful to humans. However, modern tastes do not permit the manufacture of product that is sufficiently salty. Caviar generally contains about 3.5 percent to 4 percent salt by weight. Salinity levels of as much as ten percent are required for caviar product that can be considered to be reasonably safe. Caviar products usually have pH values between 4.3 and 5.9, which again is insufficiently acid to deter the growth of all harmful bacteria.
Some organisms are well adapted to salty environments. One example is the yeast Torulopsis candida, which is found in salt brines, pickled cucumbers, marine plants and fish. It is sometimes found also in caviar. This microorganism can grow at temperatures as low as freezing point and in salt concentrations of 20 percent. However, it does not survive normal pasteurization processes of 60°C for 20 minutes. Salt tolerant microorganisms are sometimes found in impure salt. It is important that processors use only the finest quality salt available.
Table 4.8 Chemical analysis of
recommended salt (percent)
Sodium chloride (NaCl) min 99.7
Calcium (Ca) max 0.02
Magnesium (Mg) max 0.01
Sulfate (SO₄) max 0.16
Insolubles max 0.03
Moisture max 0.1
Sodium sulfate (NaSO₄) max 0.2
Source: V. Sternin, 1982
Salt quality. Salt purity affects both the effectiveness the salting process and the taste of the finished product. The table 4.8 contains recommendations for the chemical composition of salt used for processing of sturgeon caviar. Mesh of 0.8 mm should pass 100 percent of this salt; mesh of 0.5 mm should pass 95 percent.
Use of sun-dried, mined and other less pure salts can result in mold growths caused by salt-tolerant organisms introduced with the salt itself. Excessive calcium and magnesium salt impurities can result in bitter aftertastes in the product.
Fish eggs absorb salt rapidly. The salting process must be carefully monitored to ensure that only the right amount of salt is taken up by the caviar. During salting, the egg swells, becomes firmer, more elastic and gains weight. During salting and draining (while the yolk part of the egg continues to absorb salt) the egg becomes perfectly round. Note that if caviar is rinsed after salting for too long, some of the salt will be removed and the eggs can easily become watery. If rinsing is done, a light brine should be used.
Dry salting. Sturgeon caviars are dry salted by mixing 4:5 to 5 percent dry salt by weight with the eggs. The objective is to achieve 3 to 3.5 percent salinity in the final product after the excess natural brine is drained. Final product salinity will vary with the egg maturity, freshness, the temperature of the roe/salt mixture, and the length of salting time. It requires great skill to meet the targeted salinity.
Brine salting. Salmon roe is salted in saturated brine (that is, a
Table 4.9 Factors affecting salmon egg salting time in brine
Factor Effect on salting time
Increases slightly within a certain roe freshness range. As freshness is lost beyond this range time falls considerably.
Roe maturity Increases strongly, because egg membrane gets thicker. For over-mature (running) eggs, the increase is dramatic.
Brine saturation Decreases strongly at saturations lower than 90%. At saturations ≥95%, the influence is negligible.
Brine temperature Decreases slightly within the range 10 to 20’C. At higher temperatures, the effect is stronger
— egg/brine ratio
— proper agitation May increase if egg/brine ratio is less than 1/3, or brine is not fortified, or thoroughly agitated.
Egg size Increases slightly for larger eggs.
Fish species Depends on particular fish egg morphology.
Source: V. Sternin, 1982.
saturated salt solution) to produce a final salinity of 3.5 to 3.8 percent; this process is even harder to predict. Table 4.9 shows how various factors affect final product salinity.
Batches that are undersalted or oversalted often appear on the market. Some repackers attempt to correct salinity by using a second salting or rinsing, as required. However, such processes damage the product and in some cases make it unsalable. It is important to achieve the correct salinity with the initial salting process.
Another factor not mentioned in table 4.9 involves using ovaries that have been frozen before screening. The eggs absorb salt much more rapidly than eggs screened from unfrozen ovaries. They will usually reach the required salinity before the inner viscosity is high enough for a top quality product. Low salt caviar (malasol) can only be produced from the freshest, unfrozen ovaries.
Figure 4.5. Relationship between salinity and viscosity of chum salmon caviar
Figure 4.6 shows experimental salting curves for chum salmon caviar. These curves illustrate trends and should not be used as guidelines. In practice, the time needed to brine salmon eggs ranges between two minutes and 20 minutes.
Test-salting. The saltiness of the product, then, depends firstly on the grader’s evaluation of the freshness and maturity of the eggs and his ability to determine salting time. Even the most experienced caviar processors have difficulties in maintaining the desired salinity. Contract arrangements between caviar processors and buyers usually specify caviar salinity within 0.2 percent. The best way — in fact the only way — to ensure correct salinity is to test salt a sample of each batch (figure 4.7). Use a sample of about 10 ounces (300 grams) of salmon eggs. Salt it in brine at the same proportion and method as production quantities. Test the salinity every two minutes, using an instrumental measuring method. Plot a curve of the salinity over time. Then, for the production batch,
Figure 4.6. Experimental salting curve for chum salmon eggs
choose the salting time according to the curve derived from the sample readings. Measuring salinity is a simple matter, requiring basic instruments and little time. Sample curves should be prepared every time the characteristics of the roe being cured appear to change. This technique ensures that all the roe is properly salted, giving the processor the highest possible yield and return and the buyer the assurance of consistent salinity product.
For lumpfish roe, where desalting is a regular part of the process, desalting curves should be prepared in the same way, so that the final salinity of the product is controlled.
Draining and drying salted eggs is important for achieving the desired viscosity of the inner fluids of the egg. Draining of sturgeon eggs is done by putting the salted eggs on a sieve or screen in layers of 3 to 4 cm to drip and dry for periods of approximately five to fifteen minutes. The eggs can then be packed. Caviar packed directly into retail packages using filling machines should be sufficiently moist so that the eggs flow easily through the filling
equipment. Sometimes, if bulk packs are too dry to flow properly repackers will add light brine to help the flow and reduce breakage.
When sturgeon caviar is packed into institutional tins of 1.8 kilos (4 pounds), the eggs may be drained more thoroughly: these tins are traditionally filled by hand 10 to 15 mm (about 1/2 inch) above the rim. The lids are placed over the drained, tins and then slowly pressed down. Then the tins are laid on their sides for up to two hours so that the eggs drain further. finally, the tins are placed under a weight or in a screw press for several hours, so that more liquid is expelled and all the air removed from the spaces between the eggs. The tins are then wiped clean and a rubber band is put on to secure the lid.
Salmon caviar is drained in layers not exceeding 10 to 12 cm in perforated plastic buckets, or in traditional Japanese bamboo baskets. The upper layers of eggs may be too dry, the bottom layers too wet. However, during packaging eggs are mixed together, the dry eggs absorb moisture from the wet ones and the consistency of the batch is re-established. Draining time for salmon eggs depends on the egg maturity, air temperature and other factors and ranges between 30 minutes and 12 hours.
Traditional salmon drying methods expose the caviar to airborne bacteria. Other dewatering methods are centrifugation or drying with controlled currents of clean air. Drying over a vacuum chamber could further accelerate the process.
Insufficient draining is indicated by excessive juice at the bottom of the container. Too much draining and drying shows as dry eggs and clumping. Either condition may be corrected by a short rinse in light brine and subsequent draining. The addition of small quantities of vegetable oils or glycerol gives a bright, shiny appearance and prevents sticking. Properly drained salmon eggs “rattle like peas” when stirred in a bowl.
Salmon egg interior fluid viscosity is a major quality indicator. The best quality is described as having “honey-like” viscosity (see Annex, figure A.9); when squeezed, the egg does not burst easily. When the egg is forced to collapse, a viscous droplet remains.
Caviar processing plants
Caviar processing operations range from large, floating factories, to small repacking shops far from the sea and sources of fish. All plants need to maintain certain standards of sanitation and quality control. It provides guidance on many issues including designing and operating caviar processing lines, equipment, instrumentation and tools. It discusses the problems involved in water supply, brine preparation, plant sanitation and processing mechanization.
What fish makes caviar?
True caviar comes from sturgeon, specifically the Acipenseridae family in the Caspian Sea. However, roe (the eggs from the fish) are also harvested from other fish and some people consider these roe to also be caviar. There is a dramatic difference between the two, but in the United States the only requirement to be labeled as ‘caviar’ is that the product be a salted-cured fish roe. In Switzerland, however, caviar must come from sturgeon.
In other parts of the world the product must be salted-cured sturgeon roe, in order to be considered caviar. However, even within the category of sturgeon there are still several different types that could produce the caviar. These include:
• Beluga Sturgeon (buy beluga caviar)
• Russian Sturgeon
• Amur Sturgeon (Japanese Sturgeon)
• Persian Sturgeon
• Siberian Sturgeon
• Shovelnose Sturgeon
• White Sturgeon
• Sterlet Sturgeon
• Starry Sturgeon
• And many more…
If you’re interested in learning even more about all of the different sturgeon and paddlefish species (there are 27 of them) you can take a look at this article here to find out even more.
How is caviar harvested?
The process of harvesting caviar requires the extraction of unfertilized eggs (also called roe) from the fish. In the process, there are two different ways that this can be done. The first is the more classic or traditional manner, while the other is considered more “humane”.
For the traditional method of extraction the fish is actually killed in the harvesting process. For No Kill method, a for of c-section, is performed in order to remove the eggs without killing the first. We’ll take a look at each of these right here.
Are fish killed for caviar?
Many people want to know if killing the fish is essential or required in order to collect the roe. Unfortunately, the most common answer to this question is ‘yes’ because this is the traditional method by which the roe are harvested.
While it has now become possible to extract the roe without killing the fish, the majority of farms do still use the older techniques. The main reason for this is that it makes sure that the roe (and ultimately the caviar) are higher quality and more consistent. We’ll explain here.
The Classic Caviar Harvesting Method
1) extracting roe from sturgeon
The original method of harvesting caviar has actually been the same since the very beginning of the caviar time. Even though farming itself has changed, and even fishing, production, and more, the harvesting process hasn’t. And that means the old methods are still very much in use.
The traditional methods, passed down from Russian and Iranian techniques, require the killing of the fish in order to get the eggs. But as the sturgeon population has become more limited, even more people are concerned about what this process could mean to the future of the fish.
In order to keep the process as humane as possible, once the fish are full of eggs they are put into ice-water that slowly cools their body temperature. This causes them to become slower and to move less while also decreasing the amount of fat that they carry. It also makes them unconscious.
From there, the fish are killed quickly and as humanely as possible and are cleaned with purified water. The incision is then made to remove the roe from the belly of the fish.
Typically, we’ll find two roe sacks, which are removed immediately after death in order to preserve the safety and quality of the roe. If they are left too long the fish will release a chemical that damages the eggs. At this point, the roe can be cleaned and processed, while the rest of the fish can be used for other purposes, such as meat and skin.
The roe sacks, also known as skein, can be screened so that the membrane is removed and the eggs are preserved. They are then washed, filtered, drained and prepared for processing. The processing of these so-called ‘green eggs’ involves the weighing, salt-curing, and grading process that gets them ready for your table.
2) The No Kill Caviar Harvesting Method (albeit hormone driven)
Now, in the No Kill method it’s possible to remove the roe without actually killing off the fish in the process. This is considered a cruelty-free caviar or a no-kill caviar. It’s also less traditional and it’s not as popular with some of the standard farms. It actually uses hormone therapy and milking techniques or even surgery to get the eggs.
The process of harvesting caviar in these No Kills is definitely not as easy as the kill method. Because of the way that the cells within the body of the fish work, it’s essential to get the eggs out without them being fertilized or entering the water. If the eggs are unfertilized but mature they will immediately become inedible once they enter the water. And once they have been fertilized they cannot actually be collected.
This meant that there was additional work that needed to be done in order to find a way to make the process No Kill but still get high quality, safe caviar. A milking process was then created by marine biologists and German scientist Angela Kohler. This process helps to change the breeding reproduction techniques to make sure that the eggs can actually be delivered and the fish kept alive.
In order to make this process work, the fish must be monitored so that when they are ready to lay the eggs they can be injected with a specific type of hormone. This is a type of ‘signaling protein,’ which must be injected many days before they are to be harvested. It allows the eggs to separate from the membrane so that they can be more easily removed.
To help reduce stress on the fish it can still be put into a cooled pool or it can even be sedated, but will not be cooled to the point of full unconsciousness. The idea is simply to keep the fish calm and make sure that the eggs are not damaged.
It can then be washed in purified water and the eggs can be removed. This can be done through a c-section or through the vivace method.
For a c-section the belly of the fish is cut open and the eggs are taken out. Much like in a human c-section, the fish is then sewn and bandaged and then is able to be released back into the water again. It’s important that this is done extremely carefully, however, as there is danger of infection or even to the reproductive organs if it’s not done right.
For a vivace process the fish is actually ‘milked’ to remove the eggs. Also known as ‘striping’ the individual would massage the eggs out, which creates a process similar to delivery of the eggs. As soon as these green eggs are removed they must be washed, however, in a bath with water-calcium solution, which keeps them firm. Unfortunately, while this allows the eggs to be cured and eaten, it can affect the overall texture.
After either of these processes the fish can be cured and graded for sale.
3) sturgeon fish having an ultrasound
The conservation aspect of no-kill caviar is great, especially as it is helping to increase sustainability for sturgeon, which are an endangered species. When you keep in mind the fact that it takes roughly 10 years for a sturgeon to be able to produce eggs, and the fact that they can live as long as 100 years, it’s most definitely a good idea to keep them alive. It helps improve the population and also increases profits for farms by allowing them to keep the same fish year after year.
But there are some other factors to keep in mind for why farms still prefer the kill method.
Unfortunately, the no-kill methods of extracting eggs just don’t produce the same type of caviar. The flavor and the texture just are not the same and this means that caviar lovers are most definitely not impressed. Not to mention the c-section method could cause infection and infertility, which reduces the quality of the fish or results in death anyway.
The vivace method requires hormones and calcium to be added to the eggs and this means that the texture is much firmer than a traditional caviar. This is also a negative to those who enjoy the flavor of the caviar.
Next, No Kill methods of harvesting roe are actually much more expensive. There is additional equipment needed, hormones, chemicals and more. The upfront costs are extensive and the prospect of being able to use the same fish over and over again only slightly decreases the long-term costs. This is especially true when you consider that the quality of the caviar is not as good and therefore there is a lower market for it. Also, the hormones that are injected can make the caviar unsafe for some portions of the population.
What all of this means is that cruelty-free caviar may be a possibility in the future, but there is still more that needs to be done in order to make it more palatable at the moment. As a result, most of the caviar that is being produced around the world is done through the kill method.
The positive aspect of this is that caviar farming is done in actual farms, which means that wild sturgeon are not being collected for caviar. This means that the natural population of the fish is being allowed to flourish yet again. Farms can breed some of their fish for consumption and then uses every part of the fish when they do harvest the eggs.
Also, farmers are required to take care of their fish because if they don’t the eggs can actually be reabsorbed, which means that there is no caviar at all.
While there is definitely an interest in cruelty-free options and it is possible that this will become more likely in the future, for the time being, the process just isn’t ready.