ASTM E679-91(1997)
(Practice)Standard Practice for Determination of Odor and Taste Thresholds By a Forced-Choice Ascending Concentration Series Method of Limits
Standard Practice for Determination of Odor and Taste Thresholds By a Forced-Choice Ascending Concentration Series Method of Limits
SCOPE
1.1 This practice describes a rapid test for determining sensory thresholds of any substance in any medium.
1.2 It prescribes an overall design of sample preparation and a procedure for calculating the results.
1.3 The threshold may be characterized as being either (a) only detection (awareness) that a very small amount of added substance is present but not necessarily recognizable, or (b) recognition of the nature of the added substance.
1.4 The medium may be a gas, such as air, a liquid, such as water or some beverage, or a solid form of matter. The medium may be odorless or tasteless, or may exhibit a characteristic odor or taste per se.
1.5 This practice describes the use of a multiple forced-choice sample presentation method in an ascending concentration series, similar to the method of limits.
1.6 Physical methods of sample presentation for threshold determination are not a part of this practice, and will depend on the physical state, size, shape, availability, and other properties of the samples.
1.7 It is recognized that the degree of training received by a panel with a particular substance may have a profound influence on the threshold obtained with that substance (1).
1.8 Thresholds determined by using one physical method of presentation are not necessarily equivalent to values obtained by another method.
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An American National Standard
Designation: E 679 – 91 (Reapproved 1997)
Standard Practice for
Determination of Odor and Taste Thresholds By a Forced-
Choice Ascending Concentration Series Method of Limits
This standard is issued under the fixed designation E 679; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
The obtaining of odor and taste thresholds requires the sensory responses of a selected group of
individuals called panelists. These thresholds may be determined in order to note the effect of various
added substances on the odor and taste of a medium. They may also be determined in order to
characterize and compare the odor or taste sensitivity of individuals or groups.
It is recognized that precise threshold values for a given substance do not exist in the same sense
that values of vapor pressure exist. The ability to detect a substance by odor or taste is influenced by
physiological factors and criteria used in producing a response by the panelist. The parameters of
sample presentation introduce further variations. Thus, the flowrate of a gaseous, odorous sample has
an influence on the detectability of an odor. However, a concentration range exists below which the
odor or taste of a substance will not be detectable under any practical circumstances, and above which
individuals with a normal sense of smell or taste would readily detect the presence of the substance.
The threshold determined by this practice is not the conventional group threshold (the stimulus level
detectable with a probabililty of 0.5 by 50 % of the population) as obtained by Practice E 1432, but
rather a best estimate not far therefrom. The bias of the estimate depends on the concentration scale
steps chosen and on the degree to which each panelist’s threshold is centered within the range of
concentrations he or she receives. The user also needs to keep in mind the very large degree of random
error associated with estimating the probability of detection from only 50 to 100 3-AFC presentations.
1. Scope 1.6 Physical methods of sample presentation for threshold
determination are not a part of this practice, and will depend on
1.1 This practice describes a rapid test for determining
the physical state, size, shape, availability, and other properties
sensory thresholds of any substance in any medium.
of the samples.
1.2 It prescribes an overall design of sample preparation and
1.7 It is recognized that the degree of training received by a
a procedure for calculating the results.
panel with a particular substance may have a profound influ-
1.3 The threshold may be characterized as being either (a)
ence on the threshold obtained with that substance (1).
only detection (awareness) that a very small amount of added
1.8 Thresholds determined by using one physical method of
substance is present but not necessarily recognizable, or (b)
presentation are not necessarily equivalent to values obtained
recognition of the nature of the added substance.
by another method.
1.4 The medium may be a gas, such as air, a liquid, such as
water or some beverage, or a solid form of matter. The medium
2. Referenced Documents
may be odorless or tasteless, or may exhibit a characteristic
2.1 ASTM Standards:
odor or taste per se.
D 1292 Test Method for Odor in Water
1.5 This practice describes the use of a multiple forced-
E 544 Practice for Referencing Suprathreshold Odor Inten-
choice sample presentation method in an ascending concentra-
sity
tion series, similar to the method of limits.
E 1432 Practice for Defining and Calculating Individual and
This practice is under the jurisdiction of ASTM Committee E-18 on Sensory
Evaluation of Materials and Products and is the direct responsibility of Subcom- The boldface numbers in parentheses refer to the list of references at the end of
mittee E18.04 on Fundamentals of Sensory. this practice.
Current edition approved Aug. 15, 1991. Published October 1991. Originally Annual Book of ASTM Standards, Vol 11.01.
published as E 679 – 79. Last previous edition E 679 – 79. Annual Book of ASTM Standards, Vol 15.07.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.
E 679
Group Sensory Thresholds from Forced-Choice Data Sets 4.3 The panelist indicates which of the three samples is
of Intermediate Size different from the other two. A choice must be made, even if no
difference is noted, so that all data can be utilized.
3. Terminology 4.4 Individual best-estimate values of threshold are derived
from the pattern of correct/incorrect responses produced sepa-
3.1 Definitions:
rately by each panelist. Group thresholds are derived by
3.1.1 sample—a material in any form that may or may not
geometrical averaging of the individual best-estimate thresh-
exhibit an odor or taste, depending on the amount of odorous
olds.
or sapid components that it may contain.
3.1.2 medium—any material used to dissolve, disperse, or
5. Significance and Use
sorb odorous or sapid material whose threshold is to be
5.1 Sensory thresholds are used to determine the potential of
measured.
substances at low concentrations to impart odor, taste, skinfeel,
3.1.3 blank sample—a quantity of the medium containing
etc. to some form of matter.
no added odorous or sapid material.
5.2 Thresholds are used, for example, in setting limits for air
3.1.4 test sample—the medium to which an odorous or
pollution, in noise abatement, in water treatment, and in food
sapid material has been added at a known concentration.
science and technology.
3.1.5 detection threshold—the lowest concentration of a
5.3 Thresholds are used to characterize and compare the
substance in a medium relating to the lowest physical intensity
sensitivity of individual or groups to given stimuli, for ex-
at which a stimulus is detected as determined by the best-
ample, in medicine, in ethnic studies, and in the study of
estimate criterion.
animal species.
3.1.6 recognition threshold—the lowest concentration of a
substance in a medium relating to the lowest physical intensity
6. Preparation of Concentration Scale
at which a stimulus is recognized as determined by the
6.1 The concentration levels of the test substance in a
best-estimate criterion.
medium should begin well below the level at which the most
3.1.7 best-estimate criterion—an interpolated concentration
sensitive panelist is able to detect or recognize the added
value, but not necessarily the concentration value that was
substance, and end at (or above) the concentration at which all
actually presented. In this practice it is the geometric mean of
panelists give a correct response.
the last missed concentration and the next (adjacent) higher
6.2 The increase in concentration of the test substance per
concentration.
scale step should be by a constant factor. It is desirable to
3.1.8 panelists—individuals whose odor or taste thresholds
obtain a scale step factor that will allow the correct responses
are being evaluated, or who are utilized to determine the odor
of a group of nine panelists to distribute over three to four
or taste threshold of the substance of interest.
concentration steps (see Appendix X1). This will allow more
3.1.9 ascending scale of concentrations—a series of in-
accuracy in determining the threshold value based on the
creasing concentrations of an odorous or sapid substance in a
geometric mean of the individual panelists.
chosen medium.
6.3 Good judgment is required by the person in charge in
3.1.10 scale steps—discrete concentration levels of a sub-
order to determine the appropriate scale step range for a
stance in a medium, with concentrations increased by the same
particular substance. This might involve the preparation of an
factor per step throughout the scale.
approximate threshold concentration of the odorous or sapid
3.1.11 3-alternative forced choice (3-AFC) presentation—a
substance in the medium of choice. The concentration of the
set consisting of one test sample and two blank samples (as
substance may be increased two to three times for odorants or
applied to this practice).
1.5 to 2.5 times for sapid substances depending on how the
3.1.12 geometric mean—the nth root of the product of
perceived intensity of odor or taste varies with the concentra-
terms. In this method, the terms are concentration values.
tion of the substance providing the sensory response. Thus, if
x represents an approximate odor threshold concentration, then
4. Summary of Practice
a series of concentration steps would appear as follows if a step
factor of “3” were used:
4.1 A series of test samples is prepared by dispersing the
substance whose threshold is to be determined in the medium
... x/27, x/9, x/3, x,3x,9x,27x...
of interest. This concentration scale should increase in geomet-
6.4 In actual practice, the various concentrations are ob-
ric increments so that any two adjacent concentration steps are
tained by starting at the highest concentration and diluting
separated by a constant factor. At each concentration step, two
three times per step, thus providing a series of dilution factors,
blank samples consisting of the medium only are made
“V ” being the initial volume:
i
available to the panelist. The blank and test samples are
...729V , 243V,81V,27V,9V,3V , V,...
i i i i i i i
encoded so that there is no visual, audible, tactile, or thermal
difference between the samples other than code designators (2).
6.5 At each selected concentration or dilution, a 3-AFC
4.2 The panelist starts at the lowest concentration step, sample set consisting of one test and two blank samples is
which should be two or three concentration steps below the presented to panelists in indistinguishable fashion (3).Itis
estimated threshold. Each sample within the set of three is desirable to have all samples prepared and ready for judging
compared with the other two. before the evaluation session begins. (Reference (2) contains
E 679
sound practices for coding the samples, rotating the positions 9. Report
of these test and blank samples as the test proceeds, etc.)
9.1 Successful completion of the foregoing procedure pro-
6.6 If the samples are arranged in a left-center-right, or an
vides either the detection or recognition threshold of the
above-center-below order, care must be taken that the test
substance in the medium of interest in accordance with this
sample is presented in one third of the presentations in the left
practice.
(top) position, one third in the center position, and one third in
9.2 The threshold value is in concentration or dilution units
the right (bottom) position to eliminate positional bias.
appropriate for the substance tested (4).
6.7 If only one sample at a time is available, the test and
9.3 For enhanced understanding of the threshold results, the
blank samples may be presented one after another in units of
following information is recommended:
three presentations, with the test sample being randomized to
Threshold of:
be the first, the second, and the third, and requesting the
Procedure: ASTM Practice E 679 (Rapid Method)
Presentation:
response after all three samples in the set have been presented.
Number of scale steps:
Better results, however, are obtained if the test and the two
Dilution factor per step:
blank samples are available for a direct comparison, so that the
Temperature of samples:
Panelist selection:
panelist may sniff or taste back and forth at ease until a
Number of times test given:
decision is reached.
Type of threshold (detection or recognition):
Best-estimate threshold:
7. Judgment Procedure
Individual:
Panel:
7.1 The panelist begins judging with that set which contains
the test sample with the lowest concentration (highest dilution)
9.4 Refer to Appendix X1 for an example of the calculation
of the odorous or sapid substance, takes the time needed to
required and reporting.
make a selection, and proceeds systematically toward the
higher concentrations.
10. Precision and Bias
7.2 Within each set, the panelist indicates that sample which
10.1 Because sensory threshold values are functions of
is different from the two others (detection threshold) or which
sample presentation variables and of individual sensitivities,
exhibits a recognizable odor or taste of the substance (recog-
interlaboratory tests cannot be interpreted statistically in the
nition threshold). If the panelist cannot readily discriminate, a
usual way, and a general statement regarding precision and bias
guess must be made so that all data may be utilized.
of thresholds obtained by this practice cannot be made.
7.3 The judgments are completed when the panelist either
However, certain comparisons made under particular circum-
(1) completes the evaluation of all sets of the scale, or (2)
stances are of interest and are detailed below.
reaches a set wherein the test sample is correctly identified,
10.2 When 4 panels of 23 to 35 members evaluated butanol
then continues to choose correctly in higher concentration test
in air (5), the ratio of the highest to the lowest panel threshold
sample sets.
was 2.7 to 1; when the same panel repeated the determination
on 4 days, the ratio was 2.4 to 1. For 10 panels of 9 members
8. Data Evaluation
evaluating hexylamine in air, the ratio was 2.1 to 1.
8.1 The series of each panelist’s judgments may be ex-
10.3 When 26 purified compounds were tested for threshold
pressed by writing a sequence containing (0) for an incorrect
by addition to similar beers by 20 brewery laboratories (each
choice or (+) for a correct choice arranged in the order of
compound was tested by 2 to 8 laboratories), the ratios of the
judgments of ascending concentrations of the added substance.
highest to the lowest panel threshold varied from less than 2.0
8.2 If the concentration range has been correctly selected,
to 1, to 7.0 to 1 or more (6). The lowest variability was found
all panelists should judge correctly within the range of con-
with simple compounds of high threshold (sugar, salt, ethanol),
centration steps provided. Thus, the representation of the
and the highest with complex compounds of low threshold
panelists’ judgments as in 8.1 should terminate with two or
(eugenol, hop oil, geosmin).
more consecutive plusses (+).
10.4 When 14 laboratories determined the threshold of
8.3 Because there is a finite probability that a correct answer
purified hydrogen sulfide in odorless air (7), the ratio of the
will occur by chance alone, it is impo
...
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