SOP: Ranking Test

GIFSQ — Global Institute for Food Safety & Quality

Principle

Several samples are compared on the basis of a single characteristic, and each panelist places all the samples in numerical order according to the intensity of that characteristic (laboratory analysis) or according to preference (consumer analysis). A control need not be identified. The ranking method is particularly suitable when more than three samples must be compared — for comparing one treatment with others, or for comparing treatments among themselves.

Apparatus required

• Individual judging booths (identical, uniformly illuminated), each fitted with drinking water, a glass, clean towels and a basin or receptacle for expectoration
• Coloured lighting (where needed to mask small colour differences between samples)
• Stainless steel, glass or china serving dishes and cups; plain serving trays; small stainless steel forks and spoons
• Prepared evaluation cards for the ranking test

Sample preparation

Prepare all samples in exactly the same manner. Mark every sample with a three- or five-digit code number. Present all samples simultaneously (including a standard or control, if one is used).

Procedure

Present all coded samples to the panelist simultaneously

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Ask the panelist to rank the samples in numerical order according to the intensity of the specified characteristic (or according to preference, in consumer analysis): First, Second, Third, Fourth, …

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Record the sample code against each rank position

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Record comments (type of off-flavour, etc.)

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Repeat for the required panel (trained: 5–12 judges for 2–7 samples; semi-trained: 10–25 judges; untrained: 72–80 judges)

Interpretation of results

Tabulate the ranks with the treatments in columns and the replicates (panelists) in rows; total the ranks for each treatment. Where two samples were ranked equally, use the average of the ranks they would have occupied if ranked individually. Refer the rank sums to the rank-sum tables (Tables 19-5a and 19-5b of the book) to determine the significance of the differences between the observed rank sums. When the number of samples exceeds 12, or the number of panelists exceeds 20, use the expanded tables for ranked data. To compare any two samples more closely (e.g., the test sample against the best market sample), re-rank those two samples alone and re-examine.

Worked illustration from the book: five treatments (a test sample plus four market samples) ranked by 10 panelists gave rank sums of 18 (test), 16 (A), 47 (B), 28 (C) and 41 (D). The tabulated limits (Tables 19-5a/b) for 5 treatments and 10 replicates are: upper pair 20–40 at the 5% level and 18–42 at the 1% level; lower pair 23–37 at the 5% level and 20–40 at the 1% level. Rank sums below the lower limit or above the higher limit of the upper pair are significantly different: market sample A (16, below 18) is significantly superior at the 1% level, and samples B (47, above 42) and D (41, above 40) are significantly inferior at the 1% level; the test sample (18, below 20) is significantly superior at the 1% level. Sample C (28, within 20–40) is neither superior nor inferior. The book also shows reranking of the test sample against sample A alone to compare them directly.

Specimen evaluation card fields: sample codes in rank order (First / Second / Third / Fourth); comments; signature.

Precautions

• Conduct judging in individual booths so that judgements are independent; allow no communication between panel members except consultation with the panel leader on any point of doubt.
• Test in the hour after a normal meal (e.g., 10.00 a.m. to 12 noon, or 3 to 5 p.m.).
• Panel members should not smoke or chew pan or supari for at least half an hour before the test.
• Judge quickly but not hurriedly; make odour observations by sniffing before tasting.
• Allow retesting, but avoid prolonged testing; tasters may swallow or spit out samples, and should rinse between samples (or use bread or puffed rice) to remove a strong flavour.
• Assign tied ranks as the average of the ranks the samples would have occupied, and record how ties were handled.
• Keep the evaluation card simple, clearly typed or printed, with unambiguous terms and directions in the desired sequence of action.

References

Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.

Amerine, M.A., R.M. Pangborn & E.B. Roessler, Principles of Sensory Evaluation of Food, Academic Press Inc., New York (1965) — the chapter’s general sensory reference cited in the book. (The book’s own source line for the rank-sum significance tables, Tables 19-5a and 19-5b, is illegible in the available copy.)