These psychological errors are most pertinent for professional coffee cuppers and judges in competitions. Being aware of these pitfalls can help them design their evaluations to be more accurate and less susceptible to human errors. However, everyday drinkers, who probably don’t end up in formal evaluation settings, may find this list superfluous.

Nonetheless, anyone keen to take their sensory experience to the next level will find themselves behaving differently once they know what to avoid!

These psychological errors go by different names in different sources. So, if you read about them elsewhere, be prepared for the confusion. Here they are in no particular order: Order of presentation errors

First sample effect—When several samples are presented simultaneously, tasters may rate the first sample higher or lower than they would if it were in a different position.

Contrast effect—If adjacent samples are highly contrasted (e.g., one high quality then one low quality), the second sample may get scored abnormally lower (and vice versa if the low quality sample is presented first). 

The order in which the samples are presented to you and your prior knowledge of the brews are just two factors that may have dramatic effects on your evaluation of taste. Being aware of these pitfalls will make your evaluations less susceptible to human error.

Group effect—Opposite to the contrast effect, if one type of sample is placed amongst a group of different samples, the single sample is more likely to be rated like the rest of the group.

Central tendency effect—Samples placed in the center of a group of samples tend to be preferred more than the outer samples.

Pattern effect—Assessors may look for patterns amongst the samples, and, if discovered, may be biased.

For an individual, little can be done to avoid these errors, though training will help.

When working with a larger group, the errors can be balanced across the whole group.

Samples must be presented in a different, random order to each person. If every person receives a different first sample or a different middle sample, then the biases for those spots will be averaged across all the samples.

Did you know?

The first U.S. patent for decaffeinating coffee was applied for in 1906 and issued in 1908.

Error of central tendency

This is just like the central tendency effect, only it applies not to a sample within a group of samples but to the rating of a characteristic of a sample. If rating the intensity of a characteristic, such as sweetness, a person is more likely to score the sample in the middle of the scale instead of near the ends. We have a mental fear of the extremes, it seems.

Extensive training can help prevent this error by helping us not only become comfortable with the extreme ends of scales, but with recognizing the whole range of the scale itself.

Error of expectation

You find what you’re looking for. If you know you are drinking a dark roasted coffee, you’ll find flavors associated with dark roasts. Similarly, if a nearby person makes a sound or gesture after tasting the coffee, you’ll expect to find something. A good example of this was demonstrated by coloring a white wine with an odorless red dye before inviting tasters to smell the wine and identify what general type of wine they were drinking. A large percentage of the group was tricked and labeled the wine as red wine, despite their sensory experience of the aroma. Errors of expectation can be prevented by drinking your coffee (or other beverage) without knowing anything about it. This means that coffee professionals should not look at the beans, either in the green or roasted state, prior to or during evaluation of a brew.

Stimulus error

This is similar to the error of expectation. If a taster has prior knowledge of a product that is unrelated to the actual product, they will likely score a product in error. If you are going to drink a coffee from a well-regarded roaster, you’ll likely rate the coffee higher. A famous study showed that drinkers will rate a wine higher and describe it more positively if it comes from a Grand Cru bottle rather than a table wine bottle. To prevent this, tasters should be occluded from all information about a product.

Error of habituation

We are creatures of habit. If you are presented samples that are systematically changed, albeit slowly, then you tend to proffer the same rating. Thus, if a coffee that has been roasted ever so darker or lighter is presented each day, a taster may not discern it and will consequently score each successive coffee like the ones before it.

Logical error

These occur when tasters associate two or more characteristics together, which may or may not be associated. For example, lighter roasted coffees are associated with higher acidity. Thus, independent of the actual acidity of a coffee, tasters are likely to rate it

higher because of the roast level. This is pretty difficult to avoid in some cases.

Eliminating any not-gustatory sensory experiences can help. In the case of this example, nullifying the visual cue of the roast level by serving the samples in red light may help.

Ultimately, tasters must be trained away from this error.

Did you know?

In 2012, Brazil produced more green coffee than the next five largest producers combined.

Halo ef ect

Sometimes the rating of one characteristic can influence the rating of another characteristic, even when they are completely unrelated. The most serious transgression is when a taster is asked to rate the intensity of a characteristic and their liking for the product. Their subjective response will almost always influence the other ratings, just as you’d expect it to: the more a sample is liked, the higher the scores will be. This happens whether the taster’s preference is asked as the first or last question. This is why sensory tests should either be preference-based or descriptive-based, but never both.

Dumping ef ect

When asked to rate specific characteristics, tasters are limited by the choices given to them. If some other flavor is present but there’s no place to rate it, it may distract them to the point of changing the intensity of one of the options that is presented to them. Thus, they dump the experience incorrectly on an available trait. This is best avoided by having proper prior knowledge of a product and including all the relative characteristics on the score sheet.

Unfortunately, for sensorially complex foods like coffee, there may simply be too many characteristics in the experience that putting them all on a score sheet is impractical. In fact, asking tasters to rate too many characteristics seems to produce the opposite effect, causing tasters to become inhibited and underrate characteristics. 

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