Shelf Life Testing using Descriptive Sensory Profiling
Monitoring Product Change using Trained Sensory Panels
This testing method allows attributes that develop at different stages of a product's shelf life to be identified and compared. Testing may be done in ‘real time' (see our ‘milk in a can' example below) or in a single session using samples collected at pre-determined stages throughout the anticipated shelf life of the product.
Product samples are scored according to particular attributes identified and agreed on by panellists. For example, when testing coffee they might individually come up with words like ‘bitter' ‘harsh' and ‘sharp', but agree that they all describe the same sensory attribute. Because Descriptive Sensory Profiling enables panellists to quantify what they mean by particular words, it's a particularly accurate way of rating sensory attributes.
Certain attributes may be quite pronounced early on in a product's life, while others may develop during the shelf life of that product. Descriptive Sensory Profiling means that all attributes that arise and/or vary during shelf life can be identified. This stage of testing often paves the way for a later consumer testing phase, to establish absolutely the point in a product's shelf life at which it has deteriorated to such an extent that the change is detectable by consumers.
Sensory Dimensions used both Descriptive Sensory Profiling and consumer testing when asked to test the shelf life of a proposed new product: ‘milk in a can'. Designed to increase the sales of semi-skimmed milk to young adults, the ‘can' was a white plastic container with an aluminium ring pull lid. It was designed to be sold from chiller cabinets with other ‘food to go'. Supermarkets interested in the milk had requested a shelf life of at least five days in a chiller cabinet.
Storage trials were set up in a cabinet where the temperature was maintained at 5º under fluorescent light levels typical of chiller cabinet conditions. 12 trained sensory panellists evaluated the milk every day for 6 days using Descriptive Sensory Profiling. The various attributes they assigned to the milk are shown in the graph below. After 3 days of storage the panel noticed a sharp increase in ‘oxidised' and a reduction in ‘fresh' flavour, which made the milk unpleasant to drink. By Day 5 the oxidised aftertaste was so pronounced the milk was undrinkable.
Subsequent consumer tests found that while the milk was well liked by most consumers at Day 2, at Day 3 a majority (56%) found it unacceptable. With a shelf life of only two days, the milk can sadly fell short of the target shelf life the supermarkets wanted.
After investigation, the reason for the oxidised aftertaste was found to be a chemical reaction in the milk caused by light permeating the plastic container. Although alternative containers might have been an option, the project had by this time become too costly – reaching the end of its own shelf life.