How to determine product microbiological shelf–life
The length of time for which any particular food can be kept will depend on the nature of the food itself, and the preservation treatments to which it has been subjected. The type of packaging used to contain the food will also have an inherent effect. It is up to the manufacturer of the food to determine and assign the shelf life of the food they produce, keeping in mind the requirements of relevant legislation, such as the Food Safety Act 1990 and Regulation (EC) No 178/2002 (the ‘General Food Law Regulation’). These measures, in essence, require that a food must be both of the nature, substance and quality expected by the consumer, and also not injurious to health for any reason. Thus, it is illegal to sell food which has deteriorated during storage to be unfit for health reasons, or if its quality has deteriorated beyond that which would be normally acceptable. Food manufacturers go to great lengths to ensure that this does not happen.
The assignment of shelf-life is very important. If it is too short then manufacturing costs may be high and profit margins low. Also, there might be significant wastage of perfectly good product, disposed of in the belief that it is no longer fit for consumption. If it is too long then there is the potential for food quality to become poor or unacceptable, or for the growth of food pathogens to occur - and the product will not meet the requirements of food safety legislation. It is therefore important to assign the shelf-life in a systematic and scientific manner, taking all relevant factors into consideration.
Evaluation of shelf life is also important when products are reformulated; for example, minor changes in product reformulation can have a major impact on growth of microorganisms, or on product texture and stability. Any product formulation change should trigger a re-evaluation of the product's shelf life.
In determining the shelf-life of a particular food, the first pre-requisite is to know what particular characteristic of the food is going to be the limiting factor of its shelf-life. Determining that biscuits have a microbiological shelf life of several years is of no interest, if they are going to become soft and not of edible quality after 3 months. Sometimes, there may be more than one factor that needs to be assessed. For example, the shelf-life of chilled, raw meat pies might be limited by micro-organism levels, but there may also be a quality issue with rancidity development, or with water or fat migration from the meat into pastry, affecting quality.
The food processor or manufacturer should have enough knowledge of their product to be able to determine what factor is going to limit the product's shelf-life, and the approximate time for which the product will remain fit for eating (i.e. days, months or years). To fix a more precise time could require one or more of the following: