Shelf  Life Assessment

by Prof Chris Griffith

Shelf- life  assessment is an important but often undervalued/underestimated  task that food producers must undertake.  When questioned as to why a product has been given a particular shelf life auditors will sometimes hear “ because this retailer requires it “ or “ because a rival product has this shelf life “ .

The shelf –life of a product can be defined as the time during which it remains safe and desirable to eat. Thus both pathogens and spoilage organisms need to be considered.  As pathogens are considered the assessment of the shelf-life, along with supporting data, need to be considered and incorporated into the HACCP plan. The Codex approach to HACCP, which is universally adopted, and forms the basis of SANS10330:2007, is divided into 12 logic steps or stages. Stage 2 requires the producer to describe the product  and  this should be a complete description of the product covering such details as pH, Aw etc as well as  how it is processed and packaged. Also included should be its shelf- life under the prescribed conditions of storage and the latter are best covered by printed instructions on the packaging. In turn this links closely with codex stage 3 which requires the producer to identify the intended use of the product including, the likely consumers and any reasonable expected consumer abuse (known as RECA for short). It is known that some consumers may retain food beyond their shelf life and this can have very serious consequences. The rise in cases of Listeriosis in Europe has been linked to older (and hence more vulnerable) people keeping and then using food beyond its shelf life. It has prompted the UK Food Standards Agency to launch an advertising campaign specifically aimed at urging older people not to keep or use food passed its shelf life.   This emphasises the need for care in how producers decide upon their food’s shelf life.   Shelf life in relation to spoilage is also important –no producer wants to upset consumer’s because of deteriorating product quality  before the marked shelf life has ended. For both pathogen and spoilage control the product’s shelf life needs to be carefully considered in relation to “how” the product is to be stored. Care is also needed in how the shelf life is communicated to the consumer with terms such as use by, best before and sell by all having slightly different meanings and usage.

A  manufactured product’s shelf- life is best considered at the design or concept stage in new product development (NPD). The assignment of shelf life can have  a major impact on the new product’s success –if it is too short then manufacturing costs can be high (usually lowering the profit margin) if it is too long then there are potential risks for safety and quality and in turn dissatisfied  consumers who will then not buy the product again. The shelf life therefore needs to be decided in a systematic and scientific way and if necessary aspects of the product formulation (eg pH, processing, sugar content, packaging requirements etc) can be changed before it is launched.

A detailed description of how shelf life testing should be undertaken is beyond the scope of this short article and will also vary with type of product and even producer. However in general terms shelf-life can be decided by using three different approaches namely: shelf life trials, challenge testing and predictive microbiology. Each approach has its own uses and limitations but the first two will require access to microbiological facilities and testing. The third approach uses mathematical models to predict the likely growth or survival of a range of organisms in the product and even allows for what if scenarios to be assessed eg how would the shelf life change if the temperature of storage was increased or decreased by say 3°C. However it must be remembered these results are predictions only and give a cheap, useful initial idea of shelf life but would require validation .  Many of the equations are based on growth in liquid media –which would not necessarily accurately reflect growth in/on solid foods.

Shelf life determinations are unique to that product and usually cannot be extrapolated to other “similar sounding” products . Assigning a product’s correct shelf life can be key to its  commercial success and should NOT be based on unsubstantiated  requests from retailers OR what a competitor is giving their product .

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