What is sensory assessment?
Objective and subjective sensory assessment
Why use sensory assessment?
How sensory assessment operates in practice
Advantages and disadvantages
Need for expert advice
Further information

What is sensory assessment?

Sensory assessment is the use of one or more of the five senses to judge, or form an opinion on, some aspect of quality. The senses in question are sight, smell, taste, touch and hearing. Aspects of fish and fish product quality that can be assessed by these senses are shown in Table 1. By 'quality' it should be made clear that we are thinking of more than how good the fish is to eat: eating quality is perhaps the most important component of overall quality, and is greatly influenced by how well the fish is kept, whether in ice or in frozen storage, but 'quality' also includes such aspects as how valuable the fish is, how suitable the fish is for processing, and whether the fish is of the right size, is damaged or has blemishes. Sometimes an assessment is based on the use of only one sense. Thus, deciding whether a whole fish is a whiting or a haddock is done by sight alone. On other occasions two or more senses are used. For example, a suspicion that a fish is of doubtful freshness can be aroused by looking at it, an opinion that can be confirmed by smelling or tasting the fish.

The term organoleptic may be met: it relates to the properties of a food as perceived by the senses. Thus the organoleptic properties of a food are measured by sensory assessment; the term 'organoleptic assessment' should not be used.

Objective and subjective sensory assessment

In objective sensory assessment effects of personal influence are minimised by avoiding, as far as possible, bias and feelings of liking or disliking. An objective assessment should be a dispassionate and, as far as possible, accurate description of some particular aspect of quality, as in the following statements:

this fish tastes of seaweed
this fish is in size grade 3
this product is very soft
this product is straw-coloured.

I don't like the taste of this fish
I prefer product A to product B this product is delicious
I would buy this product.

Why use sensory assessment?

We need to answer this question separately for objective and subjective assessments. The former will be discussed first because it is used much more in industry.

It is essential to use objective sensory assessment wherever standards of quality need to be established, controlled or assured. Since the prosperity of most fish businesses depends on maintaining the quality of their products at a consistently high level, the importance of objective assessment is obvious. There is a strong case for all those who handle, process and sell fish to receive some formal instruction in those aspects of sensory assessment that concern them. Some aspects of quality measurable by sensory methods can sometimes be estimated also by objective non-sensory methods, described in another Note in this series. For example, instruments or chemical or bacteriological analysis can be used in some circumstances to estimate freshness or degree of deterioration. In the present state of knowledge, however, such non-sensory methods are only secondary and are not exact substitute measures of quality as understood by consumers. This is because instruments and analyses cannot yet replace human senses. Objective sensory assessment as used in industry employs the same human senses used by consumers when they make subjective judgements about quality, and is thus an intrinsically more secure way of obtaining information about quality than is non-sensory assessment; for this reason it should be used wherever possible.

Objective sensory assessment is used for two main purposes. The first is frequently met when we need to describe particular aspects of quality that are important. For example, it is often necessary to know what a product after manufacture tastes like to ensure it meets market requirements. Secondly, objective assessment is used to distinguish between two or more products. This arises, for example, during sorting by eye of fish for size, or when products on a manufacturing line are being visually inspected for faults. In these examples it is not necessary to describe what the samples are like, it is sufficient to be able to recognise that they are different in some respect.

Subjective or hedonic assessment is used in product development and market research, and is largely confined to finding out what ordinary consumers think about fish products. Together with price, the hedonic responses of consumers to fish and fish products in shops and eating places are the main factors in determining sales and repeat sales. They are, therefore, of vital interest to the industry, and it is often necessary for companies to carry out surveys of consumer likes and dislikes. Sometimes companies can carry out consumer testing themselves, but because it is a specialised activity it is often carried out by market research organisations. The information obtained is useful, for example, in deciding whether the quality of fish on offer should be improved or in indicating how products should be changed to make them more attractive to purchasers.

How sensory assessment operates in practice

Informal examination

Sensory assessment begins on board the fishing vessel and continues throughout the processing and distribution chain. In many cases important decisions about quality are made on the basis of a cursory, rapid assessment. Given the quantities of fish that have to be handled, this is inevitable and is often all that is necessary.

A deckhand faced with perhaps several tonnes of mixed commercially valuable species and unwanted rubbish from a haul must quickly recognise by sight the individual fish that are to be saved and put in separate places. This is a simple but important task requiring only a little training.

A filleter would be expected to cut fillets according to standards of quality of workmanship and of yield that are set by the factory supervisor or manager, or incorporated in a specification. This is a skilled task controlled by sight and touch and accomplished only after fairly extensive training and experience. The filleter may also have to trim or "V-cut" in order to remove bones to a quality standard set by the company or customer: here the senses of sight and touch are again involved. It is often convenient for filleters and similar operatives as part of their duties to assess other aspects of quality. For example, the presence of undesirably high numbers of parasites or of off-odours and taints can be detected by sight or smell and the unacceptable fillets can be removed from the production line at an early stage. The acuity of the operative may be enhanced by aids such as a candling table to help in detecting bones and parasites. In order to accomplish these tasks a certain amount of instruction and familiarisation is required.

Degrees of freshness and deterioration

Stale, bad or putrid fish are easily recognised by sight, smell or taste, and quality assessment of fish in this condition presents little difficulty.

There are, however, many occasions when it is necessary to assess quality at some intermediate stage of loss of freshness or some intermediate state of deterioration. For example, absolutely fresh fish commands a better price than fish that is less fresh but still not stale. Frozen fish that has suffered some loss of flavour or has developed a slight off-flavour through being stored for too long a period at too high a temperature will generally be cheaper than equivalent, fresh tasting, fish stored under good conditions. It may be necessary to check that the fish is really fresh before packaging to ensure that it will not become stale when distributed and displayed.

To assess the degree of freshness or deterioration, objective sensory assessment based on descriptions should be used. The starting point is to construct a scale of freshness or deterioration by storing fish under fixed conditions, for example well packed in melting ice. The changes in appearance, smell, taste and sometimes texture, that occur in fish after given intervals of time are described as objectively as possible by a small group of assessors. The descriptions given at each stage during the loss of freshness or during deterioration are compared and a selected set of descriptions at each stage is agreed. A set of descriptions of the odours, flavours, texture and appearance of cooked cod, from gutted fish stored in melting ice, is shown in Table 2. This set and a similar one for raw cod have been used for over 30 years at Torry Research Station and by many persons responsible for quality control in industry. It is, therefore, well used and accepted. Other sets of descriptions are available for a wide range of species and products, iced, chilled and frozen. It will be noted that none of the descriptions includes subjective expressions of liking or disliking, acceptance or rejection.

Because of the constancy of the descriptions and the clear cut distinction between the descriptions at each stage of spoilage, it is common practice to denote each stage by a number or score as shown in Table 2. The whole scheme is described as a score sheet. Each score is a useful short-hand notation for a stage of spoilage. In use, a sample in question is examined by one or more of the senses as appropriate and the findings are compared with the descriptions in the score sheet. Thus, if a sample of iced cod after cooking smells like caramel or toffee, it would be given a score of 6.

The same principles can be used to devise a score sheet and to score samples having different degrees of deterioration such as the off-flavours and poor textures that develop in badly stored frozen fish.

When using score sheets for objective assessment it is essential that the assessor, as the person carrying out the examinations is called, becomes thoroughly familiar with the procedure through training. The assessor's performance in using the score sheet must be tested periodically. Furthermore, the assessor must be interested in and dedicated to the task because it requires a good deal of concentration. Only if these conditions are satisfied can reliable and accurate results be obtained.

Amounts of blemishes and defects

The extent of occurrence of blemishes and defects such as blood clots, bruising, discoloration, processing faults, bones, skin, foreign material, guts, parasites and freezer bum can be assessed and scored visually or by touch in ways similar to those already discussed.

Grading

To meet the demands of the market increasing quantities of fish and fish products are being graded. Separating fish by size when boxing on board ship, size grading of fish for packing into cans, and selection of fillets for consumer packs are examples. Some of these operations can be accomplished by automatic weighing and grading machines, but often sensory methods are used. Grading for size involves either judging by sight and experience which category the fish falls into or, less usually, measuring the fish against a ruled scale.

Grading for freshness, degree of deterioration, colour, amount of blemishes and so on, is in principle the same. In the case of freshness, for example, fish will be allocated to grades that are defined by numerical scores on the kind of scale described in the previous Section.

In Britain and other countries within the European Community, the most important grading scheme operates at port markets as part of the price support system of the Common Fisheries Policy. This scheme includes grades of size and freshness: Table 3 shows the sensory descriptions relating to freshness for some of the species included in the grading scheme.

Other applications

Sensory assessment plays an essential role in product development.

For example, it can be used to test the responses of consumers to new products, to modified products or to products containing new ingredients. The results provide important information to guide the manufacturer towards products having the best chance of being marketed successfully.

Manufacturers, distributors and retailers sometimes need to know how long products can be kept under particular conditions before quality deteriorates below a level considered acceptable to consumers. The period is called the shelf life. It is estimated by storing the product, assessing its quality at intervals, and deciding at what point it becomes unacceptable.

Assessors and taste panels

In some circumstances, it is possible for just one sensory assessor, particularly if highly trained and experienced, to make acceptable and objective judgements of quality. Indeed, sometimes only one assessor may be available. For example, it is common practice at British ports for one person employed by the relevant Fish Producers' Organisation to carry out daily inspection and grading assessment of large quantities of chilled fish. These tasks are accomplished by rapid visual scanning of batches of fish: only in occasional cases of doubt will individual fish from a batch be examined more closely or smelled.

Inspection on production lines of fish products by company employees can be similarly covered adequately by one person examining samples regularly. Large production flows may require more than one assessor but each sample would still be examined only once.

Similarly, the manager or owner of a small buying, processing, retailing or catering business, or the skipper or mate in the case of fishing vessels, may be the only person responsible for quality assessment.

Many critical quality decisions in the industry depend, therefore, on the skills and experience of individuals acting alone. There are other circumstances, however, when it is necessary to avoid this dependence by arranging for each sample to be assessed by more than one assessor. In doing so, the risk of mistakes arising from the use of one assessor is reduced, and the assessment made more reliable. Groups of assessors operating in this way are usually referred to as taste panels, though they can use all the other senses as well as that of taste.

The ways in which taste panels can be used in the fish industry, and how panel members are selected, form too large a subject to be dealt with fully in this Note, and only a brief account of the main features can be given here. In one use, each taste panel member assesses quality of a sample objectively and independently of the others according to a scoring scheme like that shown in Table 2. The individual scores for each assessor are then averaged to give a score for the taste panel as a whole. In another objective application the taste panel members are asked to distinguish between samples on the basis of particular quality differences. For example, the members may be asked to pick out the saltiest product from a small number of products. Another important use of taste panels is where subjective opinions of a group of ordinary consumers are being sought. For example, the members may be asked how much they like or prefer a particular product. In the case of such subjective or hedonic assessment, it is essential to have a taste panel that is representative of the wider population whose views on the product are of interest.

The way assessments are conducted requires careful attention. Samples may have to be selected according to a proper statistical scheme, and coded and presented in the correct way. The results of the assessment may have to be analysed by statistical procedures. Steps must be taken to avoid problems of lack of interest, fatigue and adaptation that can affect the performance of assessors. Fatigue is the gradual loss of ability through tiredness to give reliable judgements. Adaptation is the reduction in the ability to distinguish differences in aspects of quality when assessing the same aspect repeatedly.

TABLE 1 SOME QUALITY ASPECTS OF FISH AND FISH PRODUCTS, AND THE SENSES USED TO ASSESS THEM

Sense	Aspect of quality
Sight	General appearance and condition, size, shape, physical blemishes, colour, gloss, identity
Smell	Freshness, off-odours and -flavours, taints, oiliness, rancidity, smokiness
Taste	Freshness, off-tastes and flavours, taints, oiliness, rancidity, smokiness, astringency, the primary tastes of acidity, bitterness, saltiness, sweetness
Touch (by fingers & mouth)	General texture, hardness, softness, elasticity, brittleness, roughness, smoothness, grittiness, gumminess, fluidity, wetness, dryness, crispness, presence of bones
Hearing	Brittleness, crispness

TABLE 2 SENSORY SCORE SHEET FOR COOKED COD FLESH TAKEN FROM GUTTED FISH THAT HAVE BEEN STORED IN MELTING ICE

Score	Odour	Flavour	Texture, mouth feel and appearance	Score
10	initially weak odour of sweet, boiled milk, starchy, followed by strengthening of these odours	watery, metallic, starchy; initially no sweetness but meaty flavours with slight sweetness may develop	dry, crumbly with short tough fibres	10
9	shellfish, seaweed, boiled meat, raw green plant	sweet, meaty, creamy, green plant, characteristic		9
8	loss of odour, neutral odour	Sweet and characteristic flavours but reduced in intensity	succulent, fibrous; initially firm going softer with storage; appearance originally white and opaque going yellowish and waxy on storage.	8
7	wood shavings, woodsap, vanillin	neutral		7
6	condensed milk, caramel, toffee-like	insipid		6
5	milk jug odours, boiled potato, boiled clothes-like	slight sourness, trace of 'off' flavours		5
4	lactic acid, sour milk, 'byre-like'	slight bitterness, sour, 'off' flavours		4
3	lower fatty acids (eg acetic or butyric acids), composted grass, soapy, turnipy, tallowy	strong bitter, rubber, slight sulphide		3

The descriptions and scores at the top and bottom of the table relate, respectively, to the freshest fish and to fish stored for 20-25 days in ice. Further score points down to zero can be defined as spoilage continues, but, since the fish is by that stage totally inedible, these points are of no practical significance.

Advantages and disadvantages

These are listed in Table 4. It should be pointed out that in some instances, such as subjective testing, sensory methods are indispensable.

Need for expert advice

Clearly, some aspects of sensory assessment are somewhat complicated, and before anyone attempts to introduce any but the simplest assessment scheme into a business, expert advice should be obtained.

TABLE 3 DESCRIPTIVE GUIDE TO EEC GRADES OF FRESHNESS OF WHITE FISH

In order to be placed in freshness grade E, A or B the fish should possess the following characteristics. The descriptive terms are meant to be guides and not all the characteristics described will necessarily occur together in every fish. Gill odours are particularly discriminatory.

		E	A	B	Not graded
Skin		bright; shining; iridescent (not redfish) or opalescent; no bleaching	waxy; slight loss of bloom; very slight bleaching	dull; some bleaching	dull; gritty; marked bleaching and shrinkage
Outer slime		transparent; water white	milky	yellowish-grey; some clotting	yellow-brown; very clotted and thick
Eyes		convex; black pupil; translucent cornea	plane; slightly opaque pupil; slightly opalescent cornea	slightly concave grey pupil; opaque cornea	completely sunken; grey pupil; opaque discoloured cornea
Gills		dark red or bright red; mucus translucent	red or pink; mucus slightly opaque	brown/grey and bleached; mucus opaque and thick	brown or bleached; mucus yellowish grey and clotted
Peritoneum (in gutted fish)		glossy; brilliant; difficult to tear from flesh	slightly dull; difficult to tear from flesh	gritty; fairly easy to tear from flesh	gritty; easily torn from flesh
Gill and internal odours	all except flatfish	fresh; seaweedy; shellfishy	no odour; neutral odour; trace musty, mousy, milky, caprylic, garlic or peppery	definite musty, mousy, milky, caprylic, garlic or peppery; bready; malty; beery; lactic; slightly sour	acetic; butyric; fruity; turnipy; amines; sulphide; faecal
	flattish	fresh oil; metallic; fresh-cut grass; earthy; peppery	oily; seaweedy; aromatic; trace musty, mousy or citric	oily; definite musty, mousy or citric; bready; malty beery; slightly rancid; painty	muddy; grassy; fruity; acetic; butyric; rancid; amines; sulphide; faecal

TABLE 4 ADVANTAGES AND DISADVANTAGES OF SENSORY VIS-A-VIS NON-SENSORY METHODS

Advantages

Disadvantages

Closest to what ordinary consumers experience Can be much more rapid than most non-sensory methods Assessors can use more than one sense and are, therefore, flexible instruments Good at detecting differences Can be very sensitive Acceptable for writing into specifications for quality Usually acceptable in litigation Can be non-destructive No laboratory facilities required

Assessors can become fatigued Assessors can become adapted Assessors subject to biases eg from loss of interest or from distractions Training of assessors may be lengthy Assessors not easy to replace quickly because of the need for training Can be more expensive than some non-sensory methods Not good at quantifying perceptions Interpretation of results sometimes problematical and sometimes open to dispute Several assessors required for high precision

Further information

Further information can be obtained by contacting:

The Director
Torry Research Station
PO Box 31
135 Abbey Road
Aberdeen
AB9 8DG

Tel. Aberdeen (0224) 877071
Telex 739719 MAFTRS G
Fax Aberdeen (0224) 874246

91 Sensory assessment of fish quality
92 Non-sensory assessment of fish quality
93 Handling and processing scad
94 Temperature measurement in the fish industry
95 Who does what - advice for the fish industry

Copies of all Notes are obtainable, for a small handling charge, from the above address.

BL. 5811
© Crown copyright 1989