Adaptation error: occurs when we are subjected for a long time to a same stimulus. This leads to a decrease of sensitivity towards a stimulation. For example, when we enter an environment with a characteristic odour, after some time we no longer perceive it. People who have the habit of eating salty foods feel the need to increase gradually the amount of salt to sense the same intensity of the stimulus.

Increase or decrease error: occurs when two stimuli interact with each other providing a greater (or lesser) total intensity than the two single stimuli. For example, a fresh water solution is perceived sweeter if consumed in the presence of the smell of vanilla (increase between the senses). Similarly, sugar in coffee reduces the bitter intensity of caffeine (decrease in taste).

Threshold error: it is due to the different threshold of perception (sensitivity) that individuals have, so that two people with very different sensitivity can associate a different intensity to the same stimulus.

Pathological errors: occur when the subject has temporary or permanent physiological deficits, that make him/her unable to perceive some smells (anosmia), some flavours (ageusia), some colours (colour blindness) or other sensory stimuli.

Error of expectation: derives from previous knowledge that the judge may have about the product under evaluation. For example, a trained cheese judge, will tend to “seek” a pungent note (propionic or acetic) in cheeses that have large holes (such as Emmenthaler cheese) as these two elements, the presence of holes and the pungent note, are often related to the production process.

Stimulus error: occurs when the judge is influenced by irrelevant details that “suggest” differences between the products. We all know the example of a group of sommeliers who were asked to describe a white wine sample which was artificially coloured red. The sommeliers were tricked by the colour and perceived the characteristic notes and flavours of red wines that cannot possibly be found in white wines.

Logic error: occurs when the judge uses a logical process for the evaluation of a product. For example, two samples that are coded with the production date or with a percentage value will suggest the judge to evaluate them based on this information. For the same reason, it is not a good idea for judges to know too many details of the samples, the project goals, or why the analysis is being performed.

Contrast and convergence error: these two errors occur when samples that have strong differences are evaluated together. Let’s make an example with cars. It would not make sense to ask the judges to compare a Ferrari F40 sports car with a Fiat 500 city car. Yes, they are both beautiful, they share the Italian origin and the fact that they are, in their respective category, iconic and easily recognisable items. But the evaluation of the two would be meaningless, because the two are so different (for specifications, price, etc.) that any comparison would be of no use. This is a contrast error. On the other hand, if we added an ugly, unpopular, unsuccessful medium car to the samples, i.e. the Fiat Duna, it would probably have a convergent effect for the Ferrari and the 500, showing more common traits to the latter two cars than there should be by nature.

Halo effect: it is caused by the overlapping of attributes and characteristics of the sample. For example, if we need to evaluate the crunchiness of an apple, the wrinkled appearance of its peel will inevitably affect our evaluation. Or if the apple is particularly appreciated, some of its specific attributes (eg acidity, vegetable aroma, etc.) will also be judged “positively”.

Tendency towards central value: it generally occurs with inexperienced judges who tend not to use the extreme values of a scale (too low, too high).

Presentation error: occurs because the samples are evaluated differently according to their tasting order. For example, the first sample generally obtains higher values ​​than the others, while the evaluation of the last is inevitably influenced (both psychologically and physiologically) by the first. This is why, unless there are other needs, the sensory analysis requires to randomise the samples’ sequence of presentation.

Carry-over effect: occurs during the evaluation of samples with very intense stimuli when it’s impossible to completely “reset” the stimulus before moving on to the next sample. This is the case, for instance, with spicy foods. The flavour is persistent and it will be inevitably perceived during the following evaluations.

Proximity error: occurs when two distinct attributes are evaluated in the same way (with the same intensity) because of the similarities or the mental associations that can arise between their meanings. For instance, the attributes “tender” and “juicy” in reference to a steak can be evaluated in a similar way despite being two completely different characteristics.

Mutual influence: occurs when a judge is influenced by the response of another judge, or by the judgment of the panel leader. Sensory analysis involves the use of a statistically representative number of judges during the evaluation of the products. Judges should work independently and separately otherwise the “statistical power” of the final result will be inevitably affected.

Lack of motivation: occurs when the judge attends the sessions without the right motivation. It is the most dangerous error as it transforms the judge’s precious judgment into a trivial random number similar to that of a dice roll, invalidating all the efforts made by the panel leader and the rest of the project team to perform a correct sensory analysis.