Sensory Science 101
Part II: Sensory Evaluation Methods
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© 2007 Institute of Food Technologists
What is Sensory Evaluation?
“A scientific discipline used to evoke, measure, analyze and
interpret those responses to products that are perceived by
the senses of sight, smell, touch, taste and hearing.”
Stone, H and Sidel, JL. 1993. Sensory Evaluation Practices. 2nd ed. Academic Press: San Diego.
© 2007 Institute of Food Technologists
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How is Sensory Evaluation Used?
• In a food company, sensory scientists work closely with
product developer’s to understand:
 What consumers like and why
 If consumers can tell a difference when they change a product (e.g.
substitute an ingredient)
• In academia, sensory scientists:
 Try to understand how our senses work and how our senses respond
to stimuli (both from food and chemicals)
 Improve testing methodology
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Why Is Sensory Evaluation Used?
• It reduces uncertainty and risks in decision making
• It ensures a cost-efficient delivery of new products with high
consumer acceptability
• Human observers are good measuring instruments
 People can sometimes detect odorants at levels lower than what can
be detected by an instrument
 Instruments can not measure liking (although they can be used to
determine what characteristics of a food correlate with liking - e.g. with
many beverages – up to a point - as sweetness increases so does
liking)
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Principles of Good Practice
• Facilities should be well designed
 White or off-white color
 Lighting should be controlled
 There should be good ventilation
• Samples should be prepared properly
 Temperature should be controlled and the same for all samples
 Volume served should be equal for all samples
 Samples should be served at equivalent shelf-life or time since cooking/preparation
• Experimental Design Considerations
 Samples should be labeled with random 3-digit codes to avoid bias
 Samples should be served in random or counterbalanced order
• Counterbalanced order means that if 2 samples are served, half of the subjects
receive one sample first and the other half receive the other sample first
• Counterbalancing takes into account order effects
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Sensory Evaluation Methods
• Goal is to match the right
test with the right question
Question
Method
Are products
different?
Discrimination Tests
If products
are different,
how are they
different?
Descriptive Analysis
What is the
Affective/Hedonic Tests
acceptability
of a product?
Is one
product
preferred
over another?
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Discrimination Tests
• Basic Question: Are two products different from one another?
• Basic Setup
 25-50 panelists
 Screened for acuity (keenness or sharpness of perception, i.e. can they smell
and taste well?)
 Given triangle, duo-trio or paired comparison tests
 Analysis is done using tables which compare results to chance – this analysis
ensures that the difference was real and not because people chose the
correct sample by luck/chance
• Advantage
 Quick and simple
• Limitations
 Limited results – only yes they are different or no they are not
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Discrimination Tests
• Question: Are two products different from one another?
• Triangle Test: Choose the sample that is most different
B
A
A
342
194
608
• Duo-trio Test: Choose the sample that matches the reference
Reference (B)
A
B
437
821
976
• Paired Comparison Test: Which sample is sweeter?
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B
A
035
759
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Descriptive Tests
• Basic Question: How do products differ in all sensory attributes?
• Basic Setup
 8-12 panelists
 Screened for acuity
 Trained
 Asked to rate intensity for all sensory attributes
 Analysis is done using a t-test to determine if means are statistically different
• Advantages
 Detailed quantitative information
• Limitations
 Time consuming
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Descriptive Tests
• Most food companies have a panel that is trained on each of
their products
• To train a panel takes several weeks to months
• There are several different methods of training
 Quantitative Descriptive Analysis
 Sensory Spectrum
 Flavor Profile
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Sample Ballot
305
Descriptive Tests
• What does trained mean?
• It means that the panelists are trained
to evaluate products similar to how
any instrument would give a reading
• In essence, the panelists are
calibrated so that they have an
understanding of each attribute and
the range of intensity
• For example, a trained panel would
be a given a sample of grape juice
and would be able to rate the level of
turbidity, color, viscosity, etc..
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Descriptive Tests
• Mean attribute ratings are
calculated, statistics is used to
determine if the means are
significantly different
• The data can be plotted onto
graphs – such as the spider plot –
to easily compare samples
• In this example three brands of
grape juice were compared:
 Which is sweeter?
 Which has more cooked flavor?
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Consumer Acceptance Tests
• Basic Question: Are the products liked?
• Basic Setup
 75-150 consumers per test
 Screened for product use (Do they buy the product? And how often?)
 Asked degree of liking (how much do they like it) and/or preference
questions
• Advantages
 Provides essential information – Do they like it or not?
• Disadvantages
 May be difficult to get a representative sample of consumers
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Consumer Acceptance Tests
• Acceptance Tests
 Used to measure how much people like a product
 There are several types of scales that can be used
Sample Ballot
Taste each product in the order listed. Circle how much you like the product.
The
Smiley
Scale
Quartermaster
Corp.
9-point
hedonic (liking) scale
(Used
with
kids)
(Most common)
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LIKE EXTREMELY
8
LIKE VERY MUCH
7
LIKE MODERATELY
6
LIKE SLIGHTLY
5
NEITHTER LIKE NOR DISLIKE
4
DISLIKE SLIGHTLY
3
DISLIKE MODERATELY
2
DISLIKE VERY MUCH
1
DISLIKE EXTREMELY
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Consumer Acceptance Tests
• Preference Tests
 The “Pepsi Challenge” type of test that is widely used in marketing
research
 Used to determine which product is preferred, although people have
the option to choose “no preference”
Sample Ballot
Taste each product in the order that they are listed.
Circle the number of the product that you prefer, all things considered.
470
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193
no preference
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Careers in Sensory Evaluation
• Job Titles:
 Sensory Scientist
 Sensory Analyst
 Sensory Technician
• Employers:
 Food processors
 Cosmetic and fragrance
manufacturers
 Ingredient
manufacturers/suppliers
 Academia (Higher Education)
 Consumer and marketing
research firms
 Self-employed/Consultant
© 2007 Institute of Food Technologists
• Job Responsibilities:
 Experimental design
 Sample Preparation
 Perform, analyze, and report
experimental results
 Troubleshooting
Sensory Scientist at Work!
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Want to learn more?
• Visit:
 http://www.ift.org
 http://school.discovery.com/foodscience/
• Find a Food Scientist:
 A database of IFT members who are willing to
provide more information about the field of food
science to you
 http://members.ift.org/IFT/Education/TeacherResources/findafoodscientist.htm
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Questions?
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Activity
• Triangle Sensory Test with Oreo Cookies
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References
Lawless, HT and Heymann, H. 1998. Sensory Evaluation of
Food: Principles and Practices. New York: Chapman &
Hall.
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