2. 20 3 Screening Panelists Using Simple Sensory Tests
trol work. Descriptive panels are often trained to
use scales with reference to intensity levels of
specific standards. Since prospective panelists
have not yet been trained, they should not be
expected to use a scale; but correct rankings of
intensity levels is a reasonable task to put to the
candidates.
3.1.3 Materials and Procedures, Part 1:
Odor Identification
3.1.3.1 Materials (For Each Group of 5–6
Students)
Sets of six jars with lids containing unique odors
(all labeled “A,” individually labeled with
unique three-digit codes).
Second sets of six jars with lids containing unique
odors (all labeled “B,” individually labeled
with unique three-digit codes).
Ballots consisting of two blank pages labeled
A and B.
3.1.3.2 Procedures
Begin with odor set A. Smell the odors in each of
the screw cap jars marked A. Try to identify each
odor by writing a word or two on the ballot that
best describes each odor. Be sure that the three-
digit code on the lid and the jar matches the code
for the answer line on the ballot. Form groups to
share a set of bottles by passing them around in a
circle, but do not discuss your impressions with
your neighbors, please. Next, using odor set B,
smell the odors in each of the screw cap jars. Try
to identify each order from the list of selections
provided as hints. Consider this a multiple choice
test. When you have completed both exercises,
we will discuss the correct answers, and then you
will give your ballot to the instructor or to a TA
for tabulating.
3.1.4 Materials and Procedures,
Part 2: Taste Ranking
3.1.4.1 Materials (For Each Individual)
Three samples of apple (or other fruit) juice: One
as purchased, one with 0.5 % added sucrose and
one with 1.0 % added sucrose (wt/vol).
Three samples of apple (or other fruit) juice:
one as purchased, one with 0.1 % added tartaric
acid and one with 0.2 % added tartaric acid.
3.1.4.2 Procedures
Rank the first set of three apple juices for sweet-
ness per the instructions on the ballot (3=most
sweet; 1=least sweet).
Rank the second set of three apple juices for
sourness per the instructions on the ballot
(3=most sour; 1=least sour)
3.1.5 Data Analysis
Obtain frequency counts of the numbers correct
from your instructor or website.
Taking the data from each person as a pair of
observations, perform a paired t-test on the data
from the unaided and multiple choice versions of
the odor identification. Calculate the correlation
coefficient between the two conditions using the
same data. For the taste ranking, you will con-
struct a simple table of the number of correct
rankings by the “correctness” as determined by
the number of reversals, as illustrated below.
3.1.6 Reporting
Use the standard lab report format unless
instructed otherwise. Provide a brief discussion
in complete English sentences to accompany
your graphs and tables. Answer the questions
raised below in your results and discussion
sections.
1. Odor identification results:
(a) Plot a histogram is a bar graph that shows
a frequency distribution of the data. Plot
the number of correct odor identifications
(zero to six) from each set on the x-axis
and the number of people that got each of
those scores on the y-axis (frequency).
Construct separate histograms for the free-
choice and the matching portions of the
exercise. You can use Excel or some other
graphing program to do this or you can
draw them by hand. If hand drawn, use a
straightedge for axis lines and any borders.
3. 213.3 For Instructors and Teaching Assistants
Hand-drawn graphs should be neat, with
ruler-guided lines and legible axis labels.
(b) Perform a paired t-test using (3.1) (for
additional help, see Statistical Appendix A
of Lawless and Heymann 2010) to com-
pare the mean number of correct odor
identifications in the free-choice proce-
dure with the mean number of correct odor
identifications in the matching procedure.
Was mean performance significantly
higher for one or the other method?
(c) Calculate the correlation coefficient (see
Statistical Appendix D of Lawless and
Heymann 2010) between the two odor
identification methods. Did people who
performed well in one method also per-
form well in the other method? Would you
combine individual performances in the
two methods to achieve an individual’s
total score? Why or why not? (hint: if they
are correlated they may be tapping into the
same ability).
2. Taste ranking results
(a) Check the scoring key to see if your rank-
ings were correct or incorrect. It is possi-
ble to have perfect rankings (e.g. 123), one
reversal (e.g. 132 or 213), two reversals
(e.g. 231 or 312) or complete (three) rever-
sals (321). The TA will tabulate the num-
bers correct for sweetness ranking,
sourness ranking and class totals for both.
You will need this information to answer
the following questions. Make a simple
table of the number correct vs. number of
students who scored that way for sweet-
ness and sourness rankings.
(b) Answer the following questions:
The chance of getting the ranking perfectly
correct is one in six by guessing. Did the
class do better than one-out-of-six correct?
Would you use this test in screening for
apple juice judges in a QC operation?
(Why or why not?) How could you modify
the test to make it better?
Useful equations:
(3.1)
Where t has N=1 degree of freedom for N pairs,
D
–
is the mean of the difference scores and sdiff
is
the standard deviation of the difference scores.
(3.2)
3.2 For Further Reading
Cain WS (1979) To know with the nose: keys to
odor identification. Science 203:467–470
Lawless HT, Engen T (1977) Associations to
odors: Interference, mnemonics and verbal
labeling. J Exp Psychol Human Learn Mem
3:52–57
Lawless HT, Heymann H (2010) Sensory evalua-
tion of foods, principles and practices, 2nd
ed., Springer Science+Business, New York
3.3 For Instructors and Teaching
Assistants
3.3.1 Notes and Keys to Successful
Execution
1. The percent correct in the un-cued odor ID
condition is generally 50–75 % (four out of six
is common) but somewhat higher when the
verbal cues are available. The handout or over-
head list of cues for set B must of course include
all of the odors in Set B. Some of the students
will experience the “tip of the nose effect” in
which they seem to know they are familiar with
the odor but can’t find the name (Lawless and
Engen, 1977). This is an opportunity for dis-
cussing the olfactory-verbal gap and the
difficulty in naming odors, as well as the need
for training for odor and flavor description.
2. There is a suggested list of odors for Set B in
the ballots and data sheets appendix.
3. Be sure that students understand what a fre-
quency histogram is. If they simply put the
diff
D
t
N
σ
=
( ) ( )
2 2
2 2
X y
XY
N
r
X Y
X Y
N N
⎛ ⎞⎟⎜ ⎟⎜− ⎟⎜ ⎟⎜ ⎟⎝ ⎠
=
⎡ ⎤ ⎡ ⎤
⎢ ⎥ ⎢ ⎥
− −⎢ ⎥ ⎢ ⎥
⎢ ⎥ ⎢ ⎥
⎢ ⎥ ⎢ ⎥⎣ ⎦ ⎣ ⎦
∑ ∑
∑
∑ ∑
∑ ∑
4. 22 3 Screening Panelists Using Simple Sensory Tests
raw data into Excel, it will not make the cor-
rect graph.
4. Do not allow prep personnel to add sucrose to
the desired (i.e. final) amount of apple juice.
The sugar will take up space and increase the
final volume, so the concentration will not be
accurate. The correct method is to take a
smaller volume (say 75 %) of the desired final
amount, add the sucrose while stirring, and
then top it off to get to the final desired vol-
ume. Larger size volumetric flasks are recom-
mended (2–4 L).
3.3.2 Equipment
For Part 1, odor identification, no special equip-
ment is required.
For Part 2, volumetric flasks (1 L or larger), stir
plates, stir bars, storage containers, label gun
or other means of labeling cups with random
codes. Sample trays for each student are
recommended.
3.3.3 Supplies
Part 1
Perfumer’s paper blotting strips or unscented
Q-tips or cotton balls.
Sets of 6-oz amber jars with screw caps, pref-
erably Teflon lined (12 per groups of 5–6
students).
12 liquid odorants, flavor extracts or similar
familiar-smelling liquids.
Part 2
Apple juice, about 5–6 L for class of 25;
Sucrose, commercial grade is acceptable;
Tartaric Acid, food grade. Sample cups
(30 ml or larger), rinse cups, spit cups,
water, napkins, crackers, spill control and
garbage receptacles.
3.3.4 Procedure
Part 1
Place a drop or two of each odorant on the per-
fumer’s blotter or cotton ball and place each
one in a uniquely coded amber jar. Each set
of 6 should be diverse and each set should
be of about the same difficulty level. Try to
avoid odors that some people may not be
familiar with such as lavender. All of the
items in Set B should be on an overhead or
handout. Do not show the overhead or give
the handout until SetA(the un-cued set), has
been completed. If the choices are printed
on the ballot, DO NOT give out the Set B
ballot until Set A has been completed.
Part 2
Make solutions by taking about 75 % of the
desired final volume, add the sucrose or
acid while stirring, and then top off (still
stirring) to get the final desired volume.
A volumetric flask is recommended. You
cannot simply add the sucrose to the desired
final volume because the liquid will expand
as the sugar is added and the concentration
will not be accurate.
5 l of apple juice will be enough to make 45
cups of each of the samples below (each
cup containing 20 ml sample) (Table 3.1).
Table 3.1 Suggested codes for taste ranking test
samples
Code number Contents
582 Control sample (as purchased)
683 1 % added sucrose (apple juice+10 g
sucrose per liter of final product)
815 2 % added sucrose (apple juice+20 g
sucrose per liter of final product)
869 Control sample (as purchased)
673 0.1 % added tartaric acid (apple juice+1 g
tartaric acid per liter of final product)
174 0.2 % added tartaric acid
5. 233.4 Appendix: Sample Ballots and Data Sheets
3.4 Appendix: Sample Ballots and Data Sheets
