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Sensory test: a case study
Sensory tests involve measuring the characteristics of a product through the sense organs. Specifically, smell and taste are used as real “tools” for measuring the sensory attributes of the tested product.
Sensory analysis can be applied to any product or service whose use passes through the sense organs and that has an interaction with the person: from food, to perfumes, from cosmetics to fabrics. Obviously, foods and drinks, especially those strongly characterized and with a high hedonistic content, have always been subject to organoleptic evaluation and therefore historically they are the first and most important products to which sensory analysis is aimed.
Sensory assessors are those who are able to make these measurements: they are appropriately selected and then specifically trained people who must be able to recognize without problems some fundamental flavors such as bitter, acid, savory, etc. and perceive their presence at very low threshold values.
It is not easy to be selected as sensory assessors: candidates must be non-smokers with a particularly sensitive palate that will be specifically “educated” during training, they must not suffer from rhinitis, they must not be color blind. Furthermore, they must not suffer from allergies or intolerances and, of course, they must not have any food prejudices.
The candidate assessors first undergo a training course with a Sensory Sciences expert, to learn to recognize the specific characteristics of foods and measure their perceived intensity. Only after this first screening, a “panel” of sensory judges comes out. The panel is always coordinated and guided by the laboratory manager, the “panel leader”.
The preliminary meeting
Each sensory test opens with a preliminary meeting in which the panel leader meets the assessors selected for that test and proceeds to a specific training phase in which the panel leader – together with the assessors – establishes the descriptors, that is a series of attributes that will make up the product sensory evaluation sheet.
The training, which can include one or more sessions, is specific for each product that the assessors are called to evaluate: for example, in the case of coffee, training will be carried out on mandatory parameters such as bitterness, acidity, astringency, foam, to which other parameters can be added such as color intensity, body, toasting, licorice or chocolate flavor; for a sensory test on cheese, the training will focus on flavor, the smell of hay, rennet, cooked milk.
To “train” the palate of the assessors, the panel leader lets them try some classic references for the product, for example caffeine for the evaluation of bitterness. The references are proposed in the pure state and at very low concentrations to evaluate the sensitivity of the assessors and their “threshold” values.
In the booth
Once the preliminary phase is over, it is time for the test and the assessors, generally 8 -10, enter their booths in the sensory laboratory. These are single booths equipped with sinks and computers. The booths are all white and can be illuminated with white light or red light.
The products, always distinguished by different codes, are tasted in rotation and with repetitions and the assessors must express their evaluation using a numerical scale; the data are collected with programs specifically designed for sensory tests and statistically analyzed by the panel leader.
The evaluation expressed by the sensory assessors is never a personal “taste” evaluation, but a real measurement made with a scientific method. A good panel of assessors, such as a group of well-calibrated thermometers, will come to give the same numerical evaluation to the agreed descriptors for the tested product.
Sensory test and product shelf life
The term shelf-life indicates the commercial life of the product, i.e. the time between production and sale in which it is necessary that the quality of the product remains intact. In this period, changes inevitably take place in the organoleptic characteristics of the food which lead to a progressive decay of its quality, without however compromising its health and hygiene safety. The main factors influencing the shelf life of a product are the storage temperature and the packaging.
Sensory tests are particularly useful in evaluating the shelf-life of a product: you can “measure” how certain characteristics change over time such as the friability of a biscuit in relation to packaging or for example the degree of oxidation over time of a mixture of coffee, revealed by the appearance of the “wet cardboard” flavor. This helps companies to evaluate the correct shelf-life of the product.