ASTM E679-19

Standard Practice for Determination of Odor and Taste Thresholds By a Forced-Choice Ascending Concentration Series Method of Limits

SIGNIFICANCE AND USE
5.1 Sensory thresholds are used to determine the potential of substances at low concentrations to impart odor, taste, skinfeel, etc. to some form of matter.  
5.2 Thresholds are used, for example, in setting limits for air pollution, in noise abatement, in water treatment, and in food systems.  
5.3 Thresholds are used to characterize and compare the sensitivity of individual or groups to given stimuli, for example, in medicine, in ethnic studies, and in the study of animal species.
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 of assessors with a particular substance may have a profound influence on the threshold obtained with that substance  (1).2  
1.8 Thresholds determined by using one physical method of presentation are not necessarily equivalent to values obtained by another method.  
1.9 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 14-Aug-2019
• ICS: 67.240 - Sensory analysis
• Technical Committee: E18 - Sensory Evaluation
• Drafting Committee: E18.04 - Test Methods

Relations

• Replaces: ASTM E679-04(2011) - Standard Practice for Determination of Odor and Taste Thresholds By a Forced-Choice Ascending Concentration Series Method of Limits
• Effective Date: 15-Aug-2019
• Refers: ASTM E1432-04(2011) - Standard Practice for Defining and Calculating Individual and Group Sensory Thresholds from Forced-Choice Data Sets of<br> Intermediate Size
• Effective Date: 01-Aug-2011
• Refers: ASTM E1432-04 - Standard Practice for Defining and Calculating Individual and Group Sensory Thresholds from Forced-Choice Data Sets of Intermediate Size
• Effective Date: 01-Apr-2004
• Refers: ASTM E1432-91(1997) - Standard Practice for Defining and Calculating Individual and Group Sensory Thresholds from Forced-Choice Data Sets of Intermediate Size
• Effective Date: 10-Sep-1997
• Referred By: ASTM E1432-19 - Standard Practice for Defining and Calculating Individual and Group Sensory Thresholds from Forced-Choice Data Sets of<brk/> Intermediate Size
• Effective Date: 15-Aug-2019

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: E679 − 19
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 E679; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) 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
individualscalledassessors.Thesethresholdsmaybedeterminedinordertonotetheeffectofvarious
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 assessor. 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
odorortasteofasubstancewillnotbedetectableunderanypracticalcircumstances,andabovewhich
individuals with a normal sense of smell or taste would readily detect the presence of the substance.
Thethresholddeterminedbythispracticeisnottheconventionalgroupthreshold(thestimuluslevel
detectable with a probability of 0.5 by 50% of the population) as obtained by Practice E1432, 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 assessor’s threshold is centered within the range of
concentrationstheyreceive.Theuseralsoneedstokeepinmindtheverylargedegreeofrandomerror
associated with estimating the probability of detection from only 50 to 100 3-AFC presentations.
1. Scope 1.5 This practice describes the use of a multiple forced-
choice sample presentation method in an ascending concentra-
1.1 This practice describes a rapid test for determining
tion series, similar to the method of limits.
sensory thresholds of any substance in any medium.
1.6 Physical methods of sample presentation for threshold
1.2 Itprescribesanoveralldesignofsamplepreparationand
determinationarenotapartofthispractice,andwilldependon
a procedure for calculating the results.
thephysicalstate,size,shape,availability,andotherproperties
of the samples.
1.3 The threshold may be characterized as being either (a)
only detection (awareness) that a very small amount of added
1.7 It is recognized that the degree of training received by a
substance is present but not necessarily recognizable, or (b)
panel of assessors with a particular substance may have a
recognition of the nature of the added substance. profound influence on the threshold obtained with that sub-
stance (1).
1.4 The medium may be a gas, such as air, a liquid, such as
1.8 Thresholdsdeterminedbyusingonephysicalmethodof
waterorsomebeverage,orasolidformofmatter.Themedium
presentation are not necessarily equivalent to values obtained
may be odorless or tasteless, or may exhibit a characteristic
by another method.
odor or taste per se.
1.9 This international standard was developed in accor-
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
This practice is under the jurisdiction of ASTM Committee E18 on Sensory
Evaluation and is the direct responsibility of Subcommittee E18.04 on Fundamen-
tals of Sensory.
Current edition approved Aug. 15, 2019. Published September 2019. Originally
approved in 1979. Last previous edition approved in 2011 as E679–04(2011). Theboldfacenumbersinparenthesesrefertothelistofreferencesattheendof
DOI: 10.1520/E0679-19. this practice.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E679 − 19
Development of International Standards, Guides and Recom- 3.1.10 geometric mean—the nth root of the product of
mendations issued by the World Trade Organization Technical terms. In this method, the terms are concentration values.
Barriers to Trade (TBT) Committee.
4. Summary of Practice
2. Referenced Documents
4.1 A series of test samples is prepared by dispersing the
2.1 ASTM Standards:
substance whose threshold is to be determined in the medium
E1432Practice for Defining and Calculating Individual and
ofinterest.Thisconcentrationscaleshouldincreaseingeomet-
Group SensoryThresholds from Forced-Choice Data Sets
ric increments so that any two adjacent concentration steps are
of Intermediate Size
separated by a constant factor.At each concentration step, two
2.2 CEN Standards:
blank samples consisting of the medium only are provided to
EN13725AirQuality—DeterminationofOdourConcentra-
the assessor along with one test sample. The blank and test
tion Using Dynamic Dilution Olfactometry
samples are encoded so that there is no visual, audible, tactile,
2.3 ISO Standards:
or thermal difference between the samples other than code
ISO 13301 Sensory Analysis—Methodology—General
designators (2).
Guidance for Measuring Odour, Flavour and Taste Detec-
4.2 The assessor starts at the lowest concentration step,
tion Thresholds by a Three Alternative Forced Choice
which should be two or three concentration steps below the
(3–AFC) Procedure
estimated threshold. Each sample within the set of three is
compared with the other two.
3. Terminology
4.3 The assessor indicates which of the three samples is
3.1 Definitions:
differentfromtheothertwo.Achoicemustbemade,evenifno
3.1.1 sample—a material in any form that may or may not
difference is noted, so that all data can be utilized.
exhibit an odor or taste, depending on the amount of odorous
or sapid components that it may contain.
4.4 Individual best-estimate values of threshold are derived
from the pattern of correct/incorrect responses produced sepa-
3.1.2 medium—any material used to dissolve, disperse, or
rately by each assessor. Group thresholds are derived from the
sorb odorous or sapid material whose threshold is to be
geometric average of the individual best-estimate thresholds.
measured.
3.1.3 blank sample—a quantity of the medium containing
5. Significance and Use
no added odorous or sapid material.
5.1 Sensorythresholdsareusedtodeterminethepotentialof
3.1.4 testsample—themediumtowhichanodorousorsapid
substancesatlowconcentrationstoimpartodor,taste,skinfeel,
material has been added at a known concentration.
etc. to some form of matter.
3.1.5 detection threshold—the lowest concentration of a
5.2 Thresholdsareused,forexample,insettinglimitsforair
substance in a medium relating to the lowest physical intensity
pollution, in noise abatement, in water treatment, and in food
at which a stimulus is detected as determined by the best-
systems.
estimate criterion.
5.3 Thresholds are used to characterize and compare the
3.1.6 recognition threshold—the lowest concentration of a
sensitivity of individual or groups to given stimuli, for
substance in a medium relating to the lowest physical intensity
example, in medicine, in ethnic studies, and in the study of
at which a stimulus is recognized as determined by the
animal species.
best-estimate criterion.
3.1.7 best-estimate criterion—an interpolated concentration
6. Preparation of Concentration Scale
value, but not necessarily the concentration value that was
6.1 The concentration levels of the test substance in a
actually presented. In this practice it is the geometric mean of
medium should begin well below the level at which the most
the last missed concentration and the next (adjacent) higher
sensitive assessor is able to detect or recognize the added
concentration.
substance, and end at (or above) the concentration at which all
3.1.8 ascending scale of concentrations—a series of in-
assessors give a correct response.
creasing concentrations of an odorous or sapid substance in a
6.2 The increase in concentration of the test substance per
chosen medium.
scale step should be by a constant factor. It is desirable to
3.1.9 scale steps—discrete concentration levels of a sub-
obtain a scale step factor that will allow the correct responses
stanceinamedium,withconcentrationsincreasedbythesame
of a group of nine assessors to distribute over three to four
factor per step throughout the scale.
concentration steps (see Appendix X1 – Appendix X3). This
will allow more accuracy in determining the group threshold
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
valuebasedonthegeometricmeanoftheindividualassessors.
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM
6.3 Good judgment is required by the person in charge in
Standards volume information, refer to the standard’s Document Summary page on
the ASTM website.
order to determine the appropriate scale step range for a
Available from British Standards Institution (BSI), 389 Chiswick High Rd.,
particular substance. This might involve the preparation of an
London W4 4AL, U.K., http://www.bsigroup.com.
approximate threshold concentration of the odorous or sapid
Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
4th Floor, New York, NY 10036, http://www.ansi.org. substance in the medium of choice. The concentration of the
E679 − 19
substance may be increased two to three times for odorants or choice or (+) for a correct choice arranged in the order of
1.5 to 2.5 times for sapid substances depending on how the judgmentsofascendingconcentrationsoftheaddedsubstance.
perceived intensity of odor or taste varies with the concentra-
8.2 If the concentration range has been correctly selected,
tion of the substance providing the sensory response. For
all assessors should judge correctly within the range of
example, if x represents an approximate odor threshold
concentration steps provided. Thus, the representation of the
concentration, then a series of concentration steps would
assessors’ judgments as in 8.1 should terminate with two or
appear as follows if a step factor of “3” were used:
more consecutive plusses (+).
… x/27, x/9, x/3, x,3x,9x,27x.
8.3 Becausethereisafiniteprobabilitythatacorrectanswer
6.4 In actual practice, the various concentrations are ob-
will occur by chance alone, it is important that an assessor
tained by starting at the highest concentration and diluting
continues evaluating the dilution series until multiple consecu-
three times per step, thus providing a series of dilution factors,
tive correct responses are recorded.
“V” being the initial volume:
i
8.4 The best-estimate threshold concentration for the asses-
...729V , 243V,81V,27V,9V,3V , V,...
i i i i i i i
sor is then the geometric mean of that concentration at which
6.5 At each selected concentration or dilution, a 3-AFC
the last miss (0) occurred and the next higher concentration
sample set consisting of one test and two blank samples is
designated by a (+).
presented to assessors in indistinguishable fashion (3).Itis
8.5 The panel threshold is the geometric mean of the
desirable to have all samples prepared and ready for judging
best-estimate thresholds of the individual assessors. If a more
before the evaluation session begins. (Reference (2) contains
accurate threshold value of an individual assessor is desired, it
sound practices for coding the samples, rotating the positions
may be obtained by calculating the geometric mean of the
of these test and blank samples as the test proceeds, etc.)
best-estimate threshold of all series administered to that
6.6 If the samples are arranged in a left-center-right, or an
person.
above-center-below order, care must be taken that the test
sample is presented in one third of the presentations in the left
9. Report
(top) position, one third in the center position, and one third in
9.1 Successful completion of the foregoing procedure pro-
the right (bottom) position to eliminate positional bias.
vides either the detection or recognition threshold of the
6.7 If only one sample at a time is available, the test and
substance in the medium of interest in accordance with this
blank samples may be presented one after another in units of
practice.
three presentations, with the test sample being randomized to
9.2 The threshold value is in concentration or dilution units
be the first, the second, and the third, and requesting the
appropriate for the substance tested (4).
response after all three samples in the set have been presented.
Better results, however, are obtained if the test and the two
9.3 Forenhancedunderstandingofthethresholdresults,the
blanksamplesareavailableforadirectcomparison,sothatthe
following information is recommended:
assessor may sniff or taste back and forth at ease until a
Threshold of:
decision is reached.
Procedure: ASTM Practice E679 (Rapid Method)
Presentation:
Number of scale steps:
7. Procedure
Dilution factor per step:
7.1 The assessor begins evaluating the sample set which
Temperature of samples:
Assessor selection:
contains the test sample with the lowest concentration (highest
Number of times test given:
dilution) of the odorous or sapid substance, takes the time
Type of threshold (detection or recognition):
needed to make a selection, and proceeds systematically
Best-estimate threshold:
Individual:
toward the higher concentrations.
Panel:
7.2 Within each set, the assessor indicates that sample
9.4 Refer to Appendix X1 – Appendix X3 for examples of
which is different from the two others (detection threshold) or
the calculations and reporting requirements.
which exhibits a recognizable odor or taste of the substance
(recognition threshold). If the assessor cannot readily
10. Precision and Bias
discriminate, a guess must be made so that all data may be
utilized. 10.1 Because sensory threshold values are functions of
sample presentation variables and of individual sensitivities,
7.3 The judgments are completed when the assessor either
interlaboratory tests cannot be interpreted statistically in the
(1) completes the evaluation of all sets of the scale, or (2)
usualway,andageneralstatementregardingprecisionandbias
reaches a set wherein the test sample is correctly identified,
ofthresholdsobtainedbythispracticecannotbemade.Studies
then contin
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: E679 − 04 (Reapproved 2011) E679 − 19
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 E679; 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 (´) 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.assessors. 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.assessor. 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 probability of 0.5 by 50 % of the population) as obtained by Practice E1432, 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’sassessor’s threshold is centered within the
range of concentrations he or she receives. they receive. 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
1.1 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 of assessors with a particular substance may have a profound
influence on the threshold obtained with that substance (1).
This practice is under the jurisdiction of ASTM Committee E18 on Sensory Evaluation and is the direct responsibility of Subcommittee E18.04 on Fundamentals of
Sensory.
Current edition approved Aug. 1, 2011Aug. 15, 2019. Published August 2011September 2019. Originally approved in 1979. Last previous edition approved in 20042011
as E679 – 04.E679 – 04 (2011). DOI: 10.1520/E0679-04R11.10.1520/E0679-19.
The boldface numbers in parentheses refer to the list of references at the end of this practice.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E679 − 19
1.8 Thresholds determined by using one physical method of presentation are not necessarily equivalent to values obtained by
another method.
1.9 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D1292 Test Method for Odor in Water
E544 Practice for Referencing Suprathreshold Odor Intensity
E1432 Practice for Defining and Calculating Individual and Group Sensory Thresholds from Forced-Choice Data Sets of
Intermediate Size
2.2 CEN Standards:
EN 13725 Air Quality—Determination of Odour Concentration Using Dynamic Dilution Olfactometry
2.3 ISO Standards:
ISO 13301 Sensory Analysis—Methodology—General Guidance for Measuring Odour, Flavour and Taste Detection Thresholds
by a Three Alternative Forced Choice (3–AFC) Procedure
3. Terminology
3.1 Definitions:
3.1.1 sample—a material in any form that may or may not exhibit an odor or taste, depending on the amount of odorous or sapid
components that it may contain.
3.1.2 medium—any material used to dissolve, disperse, or sorb odorous or sapid material whose threshold is to be measured.
3.1.3 blank sample—a quantity of the medium containing no added odorous or sapid material.
3.1.4 test sample—the medium to which an odorous or sapid material has been added at a known concentration.
3.1.5 detection threshold—the lowest concentration of a substance in a medium relating to the lowest physical intensity at which
a stimulus is detected as determined by the best-estimate criterion.
3.1.6 recognition threshold—the lowest concentration of a substance in a medium relating to the lowest physical intensity at
which a stimulus is recognized as determined by the best-estimate criterion.
3.1.7 best-estimate criterion—an interpolated concentration value, but not necessarily the concentration value that was actually
presented. In this practice it is the geometric mean of the last missed concentration and the next (adjacent) higher concentration.
3.1.8 panelists—individuals whose odor or taste thresholds are being evaluated, or who are utilized to determine the odor or
taste threshold of the substance of interest.
3.1.8 ascending scale of concentrations—a series of increasing concentrations of an odorous or sapid substance in a chosen
medium.
3.1.9 scale steps—discrete concentration levels of a substance in a medium, with concentrations increased by the same factor
per step throughout the scale.
3.1.11 3-alternative forced choice (3-AFC) presentation—a set consisting of one test sample and two blank samples (as applied
to this practice).
3.1.10 geometric mean—the nth root of the product of terms. In this method, the terms are concentration values.
4. Summary of Practice
4.1 A series of test samples is prepared by dispersing the substance whose threshold is to be determined in the medium of
interest. This concentration scale should increase in geometric increments so that any two adjacent concentration steps are
separated by a constant factor. At each concentration step, two blank samples consisting of the medium only are made available
to the panelist. provided to the assessor along with one test sample. The blank and test samples are encoded so that there is no
visual, audible, tactile, or thermal difference between the samples other than code designators (2).
4.2 The panelistassessor starts at the lowest concentration step, which should be two or three concentration steps below the
estimated threshold. Each sample within the set of three is compared with the other two.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from British Standards Institution (BSI), 389 Chiswick High Rd., London W4 4AL, U.K., http://www.bsigroup.com.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
E679 − 19
4.3 The panelistassessor indicates which of the three samples is different from the other two. A choice must be made, even if
no difference is noted, so that all data can be utilized.
4.4 Individual best-estimate values of threshold are derived from the pattern of correct/incorrect responses produced separately
by each panelist.assessor. Group thresholds are derived by geometrical averaging from the geometric average of the individual
best-estimate thresholds.
5. Significance and Use
5.1 Sensory thresholds are used to determine the potential of substances at low concentrations to impart odor, taste, skinfeel,
etc. to some form of matter.
5.2 Thresholds are used, for example, in setting limits for air pollution, in noise abatement, in water treatment, and in food
systems.
5.3 Thresholds are used to characterize and compare the sensitivity of individual or groups to given stimuli, for example, in
medicine, in ethnic studies, and in the study of animal species.
6. Preparation of Concentration Scale
6.1 The concentration levels of the test substance in a medium should begin well below the level at which the most sensitive
panelistassessor is able to detect or recognize the added substance, and end at (or above) the concentration at which all
panelistsassessors give a correct response.
6.2 The increase in concentration of the test substance per scale step should be by a constant factor. It is desirable to obtain a
scale step factor that will allow the correct responses of a group of nine panelistsassessors to distribute over three to four
concentration steps (see Appendix X1 – Appendix X3). This will allow more accuracy in determining the group threshold value
based on the geometric mean of the individual panelists.assessors.
6.3 Good judgment is required by the person in charge in order to determine the appropriate scale step range for a particular
substance. This might involve the preparation of an approximate threshold concentration of the odorous or sapid substance in the
medium of choice. The concentration of the substance may be increased two to three times for odorants or 1.5 to 2.5 times for sapid
substances depending on how the perceived intensity of odor or taste varies with the concentration of the substance providing the
sensory response. For example, if x represents an approximate odor threshold concentration, then a series of concentration steps
would appear as follows if a step factor of “3” were used:
… x/27, x/9, x/3, x, 3x, 9x, 27x . . .
6.4 In actual practice, the various concentrations are obtained by starting at the highest concentration and diluting three times
per step, thus providing a series of dilution factors, “V ” being the initial volume:
i
. . . 729V , 243V , 81V , 27V , 9V , 3V , V , . . .
i i i i i i i
6.5 At each selected concentration or dilution, a 3-AFC sample set consisting of one test and two blank samples is presented
to panelistsassessors in indistinguishable fashion (3). It is desirable to have all samples prepared and ready for judging before the
evaluation session begins. (Reference (2) contains sound practices for coding the samples, rotating the positions of these test and
blank samples as the test proceeds, etc.)
6.6 If the samples are arranged in a left-center-right, or an above-center-below order, care must be taken that the test sample
is presented in one third of the presentations in the left (top) position, one third in the center position, and one third in the right
(bottom) position to eliminate positional bias.
6.7 If only one sample at a time is available, the test and blank samples may be presented one after another in units of three
presentations, with the test sample being randomized to be the first, the second, and the third, and requesting the response after
all three samples in the set have been presented. Better results, however, are obtained if the test and the two blank samples are
available for a direct comparison, so that the panelistassessor may sniff or taste back and forth at ease until a decision is reached.
7. Judgment Procedure
7.1 The panelist begins judging with thatassessor begins evaluating the sample set which contains the test sample with the
lowest concentration (highest dilution) of the odorous or sapid substance, takes the time needed to make a selection, and proceeds
systematically toward the higher concentrations.
7.2 Within each set, the panelistassessor indicates that sample which is different from the two others (detection threshold) or
which exhibits a recognizable odor or taste of the substance (recognition threshold). If the panelistassessor cannot readily
discriminate, a guess must be made so that all data may be utilized.
7.3 The judgments are completed when the panelistassessor either (1) completes the evaluation of all sets of the scale, or (2)
reaches a set wherein the test sample is correctly identified, then continues to choose correctly in higher concentration test sample
sets.
E679 − 19
8. Data Evaluation
8.1 The series of each panelist’sassessor’s judgments may be expressed by writing a sequence containing (0) for an incorrect
choice or (+) for a correct choice arranged in the order of judgments of ascending concentrations of the added substance.
8.2 If the concentration range has been correctly selected, all panelistsassessors should judge correctly within the range of
concentration steps provided. Thus, the representation of the panelists’assessors’ judgments as in 8.1 should terminate with two
or more consecutive plusses (+).
8.3 Because there is a finite probability that a correct answer will occur by chance alone, it is important that a panelist continues
to take the test until there is no doubt by that person of the correctness of the choice.an assessor continues evaluating the dilution
series until multiple consecutive correct responses are recorded.
8.4 The best-estimate threshold concentration for the panelistassessor is then the geometric mean o
...