6.0 QUALITY AND SHELF-LIFE

Caviar grading judgements are based on the totality of organoleptic, chemical and bacte-riological quality indices. Organoleptic indices include taste, smell, appearance, consis-tency. Chemical indices include product salinity, residuals of restricted preservatives used, free fatty acid value, total acidity value as a measure of fat oxidation and rancid-ity, and finally, nitrogen value found in free amino acids, nitrogenous bases and other extractive substances as a measure of protein breakdown.

As with all kind of products, caviar shelf-life depends on storage conditions, i.e. time-temperature history, type of package, technological process option (preservation, pas-teurization, etc.) and overall plant and processing sanitation status. Apart from this, cav-iar shelf-life depends greatly on initial roe quality, which fluctuates from fish to fish. That is why any figures on caviar shelf-life given in this chapter, or elsewhere, are sta-tistically observed average figures, which in practice may vary considerably. For exam-ple, lightly salted, initially good salmon caviar, when vacuum packed and stored frozen is reported to remain of excellent quality for two years. At the same time, lightly salted, initially contaminated caviar in air-tight pails stored at +2°C has shown mould growth and rancidity within a couple of months.

6.1 QUALITY GRADING

It is often difficult to judge quality during organoleptical trials because of large devia-tions in the assessments. Such trials only confirm that different expert groups, e.g. of Japanese or European origin, have different ideas as to what constitutes a 'good caviar'.

Table 6-1, which grades sturgeon and salmon caviars in three grades: 'Highesf, No. 1 and No. 2, will assist quality control personnel, brokers, importers and the food service industry to make objective caviar quality assessments. The information is based on U.S.S.R. State standards and it takes into account the existing good manufacturing prac-tices in the world as well as B.C. Research experience.

Some information on pasteurized caviar is also included. Pasteurized caviar is in a grade by itself and may comply with the 'highesf grade requirements.

There are no well established traditions to judge caviars other than sturgeon and salmon. Caviar is tasted at 10-15°C. Very cold caviar temperatures mask the real organoleptical properties. Caviar taste depends greatly on fish species and its fat characteristics. By grading caviar, one is not discriminating because of one single quality index characteristic. The grading decision is based on the integral impression from organoleptical trials and objective chemical and bacteriological data.

6.2 ORGANOLEPTIC TRIALS

Table 6-2 offers a scoring system for salmon caviar organoleptic quality which may help the expert to derive the overall quality. Caviar taste and appearance are the most impor-tant of the indices which count towards the potential total score. One can notice that poor taste outgrades salmon caviar very rapid. It does not mean, however, that caviar, with a taste score lower than '6', automatically is not saleable.

Similar score tables could be developed for other caviar types. The score description is only a guideline.

The description of caviar status in Table 6-2 is very brief. The decision to assign a cer-tain score to the sample is still quite subjective. Table 6-3 can be used as a formal key to assist in making the final judgement on caviar grade based on compliance with two conditions: taste plus smell score and total quality score. The quality indices in Table 6-2 are arranged in the recommended order of making judgements when samples are pre-sented.

 

TABLE 6-3

GRADING USING TABLE 6-2 SCORES

If a single quality index does not comply with grade No. 2 requirements then independ-ent of the total score the product is outgraded.

We realize that the score system is very formal and should be used cautiously. The sys-tem was successfully used over many trials. Caviar was graded No. 1 or No. 2 only if minimum scores for each grade were met. Organoleptic taste panelists should be trained in profound understanding of the quality assessment checklist (Table 6-1) and the nature of potential defects. Chapter 6-3. Only then can they make use of the 10 score scale. Training of panelists is essential to avoid the semantic difficulties in the interpretation of the words in Table 6-1 and 6-2. It is essential to present to the panel samples of equal salinity, otherwise the overwhelming impact of salinity may distort the impressions from all other quality indices. The often used ranking tests show the least dispersion. The triangle test, which is designed to identify the odd sample, is used to clarify a cer-tain sample grade in comparison with samples of a well defined grade.

Organoleptic checks during shelflife storage are made at least once every 2-3 months for a given lot, unless otherwise needed. It is difficult to define a lot. The lot is determined during processing and initial packing. A lot comprises homogeneous packages, packed on the same day at the same processing site. The quality certificate is supposed to verify this.

When lifting the lid from bulk sturgeon caviar tins to take a sample, one should tap lightly over the lid so eggs won't adhere to the lid and the lid can be put back in place easily. First of all the smell is examined and next the surface of the eggs is visually ex-amined. Using a spatula the sample is taken in the middle of the tin from a 15-20 depth. To be representative, the samples are taken for examination from different packages and mixed into an average sample. This applies to chemical, bacte-riological, taste, impurities, consistency and egg membrane examinations. Colour and appearance are estimated in bulk.

6.3 DEFECTS

The technology and conditions at most caviar handling sites do not provide for aseptic packaging of low salt caviar. The use of chemical preservation improves shelf-life only marginally. Both oversalting or pasteurization as alternative solutions are detrimental to caviar taste. Defects may appear while processing or during storage or could be due to the combined effect of both processing and storage.

Whichever technological option is chosen, the time-temperature impact sooner or later brings up typical caviar defects. Some of them are common for all caviars, some are typical only for specific caviar types. A review of these defects and possible causes of their appearance is given below. Caviar defects can seldom be fixed. Usually defects re-sult in product downgrading or total discarding (outgrading).

One of the most common defects for both sturgeon and salmon caviars is sharpness in taste with slightly detectable soury aftertaste. This condition further develops into to-tally unacceptable and offensive sourness and stinginess.

It is mainly caused by microbiological and enzymatic spoilage. It starts with changing in taste and is followed by offensive smell, and loss of elasticity of egg membranes. Egg shape collapses, a sticky slimy juice appears between the eggs and on the product sur-face. The slime then develops into visible mould and yeast colonies which penetrate the bulk and grow on the package walls. Salmon caviar is more susceptible to this microbi-ological spoilage then sturgeon caviar. In extreme cases, egg membranes rupture, mas-sive release of juice follows and strong sulphuric, ammoniacal and methylaminic smells appear as a result of protein disintegration.

Salmon caviar colour darkens to brownish tones and broken egg membranes appear in abundance.

At the very early stages of this process/ caviars can be reconditioned to improve or-ganoleptic properties and then downgraded, thus still remaining a saleable item. The re-conditioned product should however always comply with the existing product safety regulations, and undergo mandatory expert evaluation.

Reconditioning is done by quick multiple rinsing in light brine (5-6%) at 12-15°C, thor-ough draining and repacking. The reconditioned product should be consumed within days. Reconditioned caviar, while edible, is of low grade. The idea of such recondition-ing is to get rid of the water soluble acids and thus improve the taste and smell. If the spoilage process progressed to weakening of the egg elasticity and/or started in the yolky egg interior and spread throughout the egg mass, reconditioning is impossible.
The most trivial defect is undersalting or oversalting of caviars. The issue was discussed in Chapter 4.

A typical defect of sturgeon caviar appears, as a result of extremely long shelf-life and temperature abuse, in the form of little white crystalline non-soluble, odour free bodies 0.1 to 1 mm in size. They appear in pasteurized sturgeon caviar if the later was pasteur-ized after prolonged storage of the unpasteurized bulk. These crystals look like "wheat-lets" and are distributed throughout the caviar mass. The larger ones have an irregular shape with protruding spiny edges.

They appear as a result of protein hydrolysis and consist mainly of tyrosine and other amino acids (Figure 6.1a). High salt content enhances this phenomenon.

The appearance of those crystals is a sign that the product is not useable because of gen-eral spoilage. However, the crystals are not harmful. Removing them by reconditioning is impossible.

FIGURE 6-1: Caviar Defects

A bitter taste or aftertaste in caviar may be caused by many reasons. Firstly bitterness is noticeable in oversalted products or when poor quality salt, which contains excessive magnesium and calcium impurities, is used. Some preservatives, like urotropine, may cause slight bitterish-stingy aftertaste. Sockeye and coho caviars have a slightly bitter natural aftertaste, which is caused by some unstable fatty acids specific for these spe-cies. This shortens substantially sockeye and coho caviar shelf-life.

Finally bitterness is a result of fat oxidation and hydrolysis. Sturgeon caviar is some-what less susceptible to this kind of deterioration because the fat droplet is concentrated in the middle of the egg whereas in salmon eggs fat droplets are distributed throughout the yolk.

Bitterness caused by fat oxidation and hydrolysis is easy to distinguish from bitterness resulting from poor quality or excessive salt with the former the bitterness is lasting and it has a tickling affect in the throat. In the either case the bitterness is short lived.

Caviars may have mild to strong off-tastes which are specific to the fish habitat or feed-ing patterns. The most well known are the so-called 'grass/ or 'mudd/off-tastes of stur-geon caviars, particularly of Caspian osetra. Beluga and sevruga caviars do not show noticeable off-taste. In the trade many argue that these off-tastes, when expressed mildly, contribute to an original taste bouquet, which is then called 'nutty' and should be appreciated.

These off-tastes appear with sturgeon, that before they were caught, were living in shal-low, stagnant waters overgrown with weeds, or with a silt bottom. Tastes may change in season and depend on area of harvest. If the off-taste becomes strong, caviars are down-graded. The only way to remove partially these off-tastes and off-odours is to keep the sturgeon alive in running water for 15-20 days before slaughtering. These off-tastes have been masked in caviar by artificial flavouring.

Salmon caviar off-tastes are caused by inadequate processing or fishing practices such as subjecting caviar after salting and before packing to polluted air (gasoline, smoke) or poor sanitation. Metallic off-tastes result from the use of tins which are not appropri-ately protected with lacquer and stored for a long time.

When undersalted salmon caviar (1.5-2.5%) is subjected to temperature abuse, a slight sulphuric smell (similar to rotten eggs) may sometimes appear very quickly, before other spoilage indications. If noticed in the very early stages, within days after packing, salmon caviar could be quickly rinsed in brine and resalted with fine salt. The recondi-tioned caviar should be consumed within days. The product has to be downgraded, its safety checked according to the existing regulations and an expert evaluation and certi-fication is mandatory. Individual caviar-lot colour fluctuations are not considered de-fects, unless they are related to general spoilage, e.g. darkening of salmon or whitefish caviars. With sturgeon caviar, colour changes during storage are hardly noticeable.