GUIDE FOR THE SELECTION, TRAINING AND MONITORING OF SKILLED VIRGIN OLIVE OIL TASTERS
COI/ T.20/ Doc. No 14/Rev. 4
The purpose of this standard is to provide panel leaders with essential rules for selecting, training and monitoring the selected tasters on their panel.
2. SCREENING OF CANDIDATES
Screening shall be carried out by the panel leader who shall personally interview the candidates to become familiar with their personality and surrounding environment. The physio-psychological conditions that have to be met are not very rigorous since, theoretically, any normal person should be able to perform this work. Factors such as sex, age, specific habits (smoking), etc. have been superseded nowadays by others such as health, personal interest and having time available for the work.
During the interview, the panel leader shall explain the characteristics of their task to the candidates and approximately how much time it will take up. He or she shall then glean information from the candidates allowing assessment of their interest and motivation and how much real time they have available. The following questionnaire could help as a reference.
Please, answer the following questions: YES / NO
- Would you like to be involved in the work on this subject? …. ….
- Do you think this work could contribute to the quality improvement of foodstuffs on the domestic and international fronts? …. ….
- If so, why?1/
- You should be aware of the fact that you will have to taste oils when called upon to do so. Would you be prepared to do this? …. ….
- Would you like to compare your olfactory- gustatory skill with that of your colleagues? …. ….
- Are you available time-wise?
Are you independent enough to organise your daily work as you wish? …. ….
- If you are dependent upon a superior, do you think that if you had to absent yourself from your usual job for anything up to half an hour, on several occasions over a successive number of days, you would be allowed to do so? …. ….
- Would you be able to make up for any time lost in your job due to your participation in the
sensory analyses? …. ….
Do you think you should be remunerated for this work?
- In what way? ……………………………………………………..
Describe what could be gained from the organoleptic assessment of any foodstuff, or, if you wish, of olive oil.
The panel leader shall use this information to screen the candidates and shall reject those who show little interest in this kind of work, are not readily available or who are incapable of expressing themselves clearly.
3. DETERMINATION OF THE DETECTION THRESHOLD OF THE GROUP OF CANDIDATES FOR CHARACTERISTIC ATTRIBUTES
The panel leader shall carefully choose four oils, one each of which is considered to be representative of one of the following attributes – fusty, winey, rancid and bitter – with as great and clear an intensity as possible.
The panel leader shall prepare a series of samples of each of the oils at descending concentrations (1:2) by making successive dilutions in a medium (refined oil or paraffin).
The series shall be considered completed when no difference can be detected between two successive samples of the series and the medium. The panel leader shall then choose the seven samples prior to these last two from the prepared series.
Enough samples should be prepared for the number of candidates.
Paired comparison tests shall be carried out to establish the mean threshold of the group, up to a total of 8 pairs of samples per candidate which shall be randomly presented in successive, independent tastings (the pairs comprise one each of the seven samples chosen and a blank medium, plus one pair of blank mediums). After each tasting, the candidates shall be asked whether the two samples are identical or different.
Upon completion of the test, the panel leader shall note down the correct answers of the set of candidates for each concentration and shall express them as a percentage. The leader shall plot the concentrations tested along the x-axis and the percentages of correct answers along the y-axis and then, by interpolation of the curve, shall determine the detection threshold which is the concentration corresponding to 75% correct answers. A practical example of this procedure is given in Figure 1.
This “threshold concentration”, which may be different for each initial oil because it depends on the intensity of the attribute present, should be similar for the different groups of candidates to various panels; it is not linked to any habit or preference. Consequently, it is a point of reference common to any normal human group and may be used to homogenise the various panels on the basis of their olfactory-gustatory sensitivity.
If the above procedure is repeated for the three remaining attributes on the basis of their respective thresholds which are also calculated as indicated above, scales with similar aromatic intensities for each stimulus will be obtained for all the laboratories, even though the defects of the initial oils may be perceptible at different intensities.
This threshold concentration shall be C10 in the series of samples prepared to select tasters by the intensity rating method (section 4).
4. SELECTION OF TASTERS BY THE INTENSITY RATING METHOD
n the selection procedure, there should be two to three times more candidates than those required for the panel so that the people with the best sensitivity or powers of discrimination can be picked out. It is always advisable to use the same product as the one that is to be subsequently analysed.
When selecting the method, it should not be overlooked that, apart from being effective, the procedure adopted should be as economical as possible as regards the quantity of oil, the number of samples to be used and the time spent on selection. The effectiveness of a selection procedure lies in the choice of the optimum levels of the following three dependent variables: (a) “cost” determined by the number of tests, (b) “proportion” of potentially suitable candidates who by chance have been unfortunately eliminated during screening and (c) “proportion” of candidates who by chance have got through the selection process although unsuitable material.
The selection procedure chosen is as described by F. Gutiérrez Rosales et al. (2).
– Liquid paraffin (DAB, PhEur, BP, USP) or oily medium without taste or odour (recently refined olive oil or another similar oil).
– Oils: fusty, winey, rancid and bitter.
Start the selection process with 25 candidates, in accordance with the methodology described hereafter for each stimulus:
On the basis of the threshold concentration obtained for the group, proceed as follows:
Prepare a series of 12 samples in such a way that the “threshold concentration” holds the 10th place in this scale. Naturally, the 11th and 12th concentrations will be more diluted, as a result of which it will be more difficult to detect the presence of the oil possessing the selected attribute.
Taking the C10 concentration as the basis, the remaining samples can be prepared in accordance with the following formula:
C10 x an, where “a” is a constant, the dilution factor, which is equal to 1.5, and “n” is the exponent which varies between 9 and -2.
Example: if the threshold obtained for rancid oil is 0.39, then C10 = 0.39. Since “a” = 1.5, the series of samples would have the following concentrations:
Sample1 2 3 4 5 6 7 8 9 10 11 12 Conc. 14.99 10.00 6.66 4.44 2.96 1.97 1.32 0.88 0.58 0.39 0.26 0.17
(1) Prepare 12 coded tasting glasses (one series per candidate) and pour 15ml of each of the concentrations prepared into each glass.
(2) It is advisable to leave these glasses covered with a watch-glass in the tasting room at a temperature of 20–25oC for at least an hour before starting the tests in order for the oil to reach ambient temperature.
(3) The leader shall then arrange the 12 tasting glasses of each series in a row in descending order of concentration.
The next step is to ask each candidate to perform the test on their own, in accordance with the following instructions:
4.2. Instructions for candidates
The 12 tasting glasses lined up in front of the candidates contain dilutions of the fusty/muddy sediment and/or winey and/or rancid and/or musty and bitter stimuli. The distinguishing factor between the contents of the tasting glasses is their intensity. The glass with the greatest intensity is on the far left-hand side and the rest of the glasses are placed in descending order of intensity towards the right. The last tasting glass on the right may have such a weak intensity as to be impossible to detect.
Proceed as follows: Become familiar with the odour and taste of each of the tasting glasses in the series. To do so, begin smelling and tasting at the right-hand side (no. 12) and try to retain the intensity of all the odours and tastes, without becoming overtired.
When you feel that you have got used to the scale of concentrations of the odour and taste, leave the room.
Meanwhile, the leader shall remove one of the tasting glasses from the series and shall place it on a level with the last one on the right-hand side (no 12), moving all the others together so as to fill in the space left. Then return to the room and carry on with the test.
The test involves the following:
The tasting glass withdrawn from the series has to be put back in its exact place. To do so, smell and taste it and compare it with the others as often as wished, bearing in mind that if it is to be replaced correctly its intensity must be stronger than the sample on its immediate right and weaker than that on its left. This test will be repeated with three other glasses.
Each candidate shall be issued a form, in addition to the instructions just described, in order to make the test and the collection of the replies easier.
SELECTION OF CANDIDATES
Test nº ……………………… Attribute …………………………………………..
The glass taken out belongs to position n ……………………………………………………….
Date …………………………….. Name ……………………………………………
4.3. Obtaining the result
The panel leader shall record the data for each of the candidates in the following manner to facilitate their arrangement:
Name of candidate Attribute studied Nº of orden given (K’) Exact Nº of order (K) Grading (K’ – K)2
__________________ ________________ __________________ _____________________________ _________________
__________________ ________________ __________________ _____________________________ _________________
4.4. Statistical scoring procedure
In this particular selection case, the tasting glasses that have to be replaced in their exact position shall be the same for all the candidates. According to the statistical calculations done for this purpose, they shall correspond to the following positions in the order of the series as regards each attribute:
Fusty (At)/Muddy sediment (B) and/or Winey (Av) and/or Rancid (Ra) and/or Musty (Mo) y Bitter (Am)
Glass nº Glass nº Glass nº Glass nº
(10,5,7,2) (11,3,8,6) (7,4,10,2) (6,3,11,9)
The number corresponding to the position of the glasses in the order of the series may not vary since the statistical calculations for this test have been done with an eye to the probability of the glasses being randomly replaced in their exact position.
In order to make it extremely difficult for any information to be passed on from one candidate to another, the panel leader shall ensure that:
1) THERE IS NO POSSIBLE MEANS OF CONTACT BETWEEN THE CANDIDATES. DIFFERENT CODES SHALL BE USED FOR EACH CANDIDATE.
2) THERE IS NO WAY IN WHICH THE CANDIDATES CAN FIND OUT THE POSITION OF THE GLASSES WHICH HAVE BEEN WITHDRAWN.
3) EVEN THOUGH ALL THE CANDIDATES SHALL BE PRESENTED WITH THE SAME GLASSES INDICATED EARLIER ON, THE ORDER IN WHICH THEY ARE HANDED OVER TO EACH CANDIDATE SHALL VARY.
Each candidate shall then be given a score, depending on their performance, in the
Let ei , ei , … ei be the 12 glasses with the 12 corresponding 1 2 12
concentrations of attribute “i” (i may be any one of the 4 attributes: fusty, winey, rancid and bitter) arranged in descending order of intensity.
Let ei be one of the glasses picked and K’ the position it is allocated K
by the candidate when replaced in the series. Therefore, the values of K and K’ are whole numbers between 1 and 12 inclusive, corresponding to the real place number of the glass chosen and that allocated by the candidate respectively.
Let T (maximum permitted deviation) be a value set beforeh