Sensory labs: scientific aspects

Implementation of sensory tests under controlled conditions in the sensory lab

People can easily be distracted and influenced in their perception. Compared to the functionally superior senses of hearing and seeing, the chemical senses of smell and taste provide less clearly structured and reliable sensations. It is difficult to discern in a differentiated manner substances that are, for example, contained in food or beverages. Hence, in the context of sensory tests it is highly important to eliminate as many potential disturbing factors as possible. Experience has shown that this can only be achieved under strictly standardized laboratory conditions.

For sensory tests to be run professionally it is not sufficient to have testees and to use appropriate testing methods. Only if also rooms and equipment suffice certain (structural and technical) criteria, scientifically significant data can be obtained.

To eliminate possible disturbances of the testees' senses, particular equipment features are required that are not commonly shared with other types of laboratories. This includes amongst others single test cabins, special lighting technology, noise-absorbing building materials, a seperated preparation room and if needed with a kitchen and hatches leading to the test cabins. The standardization of the tests is partly ensured by the identical equipment of the test cabins, the regulatable indoor climate and the lighting situation that is individually controllable and independent of the daytime and the cabin arrangement.

Objectives

During testing, the volunteers should…

• … feel at ease with an ergonomic sitting position, comfortable chairs and a pleasant climate.
• … find uniform, standardized test conditions.
• … not experience any psychological influence.
• … not be distracted or interrupted (meaning the absence of disturbance factors)

General framework

Elimination of disturbance factors

The disturbance factors include anything that has an influence on the testees' perception or may cause any distraction in general.

Therefore, measures have to be taken that prevent or minimize the following aspects:

• Ambient noise
  • Test cabins not in immediate vicinity of air conditioning or manufacturing plants
  • Avoidance of internal noise pollution
  • Test room not directly facing towards street – avoidance of external noise
  • Noise-absorbing floor covering
• Foreign odors
  • Exhaust/ventilation system with an adequate air exchange per hour
  • Difference in air pressure between preparation and test room: The pressure should be higher in the test room.
  • Use of olfactory inert materials for floors, wallpapers and cabins (e.g. no carpet as floor covering)
• Visual stimuli (e.g. light reflexes, shadows, irritating colors)
  • Exclusion of daylight
  • Neutral color selection (white, light grey) for furnishings, ceilings and walls
  • Red or green lighting to mask different product colors
  • White light with an illumination intensity of 1000–1500 lux
  • Even and glare-free illumination
• Influences resulting from room climate
  • Constant temperature (air conditioning)
  • Constant humidity
• Test neighbors influencing/distracting each other during single-person tests
  • Single cabins or partition walls between test stations
• Influencing of test persons due to contact with personnel or view into the preparation room
  • Strictly separated preparation room without direct access to the test room
  • Hatches allowing only minimal view into preparation room

Standardized test conditions

Tests under standardized conditions help to achieve high-quality results in a time- and cost-efficient manner. Additionally to ensuring uniform lab conditions, it is important to standardize the sample preparation (product-dependently). For example at tasting, beer by default should have another temperature (+6 °C) than red wine (+16 °C). The following areas can be standardized:

• Personnel ergonomics
• Test environment
• Preparation
• Sample coding
• Test procedures
• Schedule
• Evaluation

Examples:

• Tasting with constant product temperature
• Identical sample amounts and forms of presentation for all testees
• Identical test station equipment
• Identical lighting situations at all test stations
• Test execution according to predefined schedule and procedure

Appropriate testees

Depending on the question that should be answered by a test, sensory trained internal or external expert panels, own staff members or untrained consumers may be chosen as testees.

Inexperienced laymen (consumers or staff members) are used for affective testings. In this type of test products are examined in terms of popularity, preference or acceptance. Hereby, the subjective product perception should be identified.

Analytical tests are carried out with experienced testees. They deliver objective results in terms of identification and quantification of sensory product characteristics. Additionally, this type of testing is used to determine differences between multiple products.

Testees performing the latter kind of tests are sensory trained employees or members of external panels. They passed for example a basic training according to DIN 10961:

• Distinguishing the basic aroma types
• Difference tests
• Aroma perception
• Threshold testing

It is important to regularly train and check the sensory abilities. Some tests require panels of so-called expert examiners who have additional product-specific knowledge.

Appropriate test methods

The “right” questions have to be asked and then answered utilizing appropriate methods. Essentially, there are three different kinds of test methods:

• Hedonic test procedures
• Discriminative methods
• Descriptive methods

Difference tests and descriptive testing are summarized as analytical methods.

Hedonic or affective test procedures are used to evaluate subjective product perceptions. The following methods are commonly differentiated:

• Acceptance tests
• Preference tests
• Aversion tests
• Boredom tests
• Permanent preference tests

Anaytical test methods are used to evaluate the product awareness. There are the following method subtypes.

Discriminative methods (difference tests)

Multiple products are compared to each other. This methods are used, for example, if raw materials or production methods should be changed or if complaints were registered. Examples for difference tests:

• Ranking test DIN 10963
• Triangle test ISO 4120
• 2 of 5 testing
• Pairwise difference testing

Descriptive methods

Sensory properties are described and the respective intensities are quantified. This methods are an important part of the product development. Examples:

• Simple descriptive test DIN 10964
• Descriptive analysis with following quality evaluation DIN 10969
• Investigation of profiles DIN 10967;
• Quantitative descriptive analysis (QDA)
• Texture profile analysis
• Free-choice profiling

Benefit

The testees can fully focus on the samples and product variants. This allows valid, reproducable and statistically evaluable test results to be generated. Capacities are used efficiently since unnecessary and costly test repititions are prevented.