262 Chilled foods should then be confirmed by a scientific approach outlined in Section 10.4. Once the shelf-life has been determined there are a number of factors which will affect shelf-life as described below. These also need to be considered at the product development stage to ensure that they are under control during routine production of the product 10.2.2 Raw materials The raw materials used in the preparation of a product will influence the biochemistry and microbiology of the finished product. In order to achieve a consistent shelf-life, the quality of the raw materials needs to be standardised and the attributes most likely to affect product shelf-life should be laid down in specifications. Variations in the quality of raw ingredients can lead to variations in the final product which may affect product shelf-life. Variations in raw material can occur for a number of reasons: natural variation, variety change, a hange of supplier, seasonal availability or pre-processing applied to raw materials. The manufacture of coleslaw provides an example of where shelf-life can be influenced by the seasonal availability of freshly harvested cabbage which has a low yeast count, whereas cabbage from cold storage has a higher yeast count. Use of cabbage from cold stores results in coleslaw with a markedly shorter shelf-life owing to the higher starting levels of yeast introduced via the If an ingredient for a raw product does not meet an agreed specification, e.g for levels of microorganisms, it is still possible to use the ingredient for a different purpose, e.g. to be added to a product before cooking, provided there is no compromise to food safety. The likely consequences of using higher levels of organisms can be evaluated using predictive models(Section 10.3). Tolerance limits for those ingredients that exert a key preservative effect in the final product, such as the percentage of salt, need to be established during the development of the product or in challenge testing(see Section 10.6) and be stated in the product process and formulation specifications. Any variability in the levels of these ingredients due to inaccuracy in weighing ingredients during routine production will affect the shelf-life achieved. Ingredients which are crucial to product safety or stability during the assigned shelf-life should be identified using product hazard analysis(Leaper 1997) and the levels of these ngredients must be controlled during routine production. For example,for chilled MAP foods a salt level of 3.5% in the aqueous phase can be a key controlling factor for these foods and the salt level must be monitored for each batch of product manufactured(Betts 1996) Product formulation can be used to overcome natural variability of critical factors in raw materials and thereby reduce the variation of the final product. The pH is one of the most important factors affecting the degree of heat processing required to achieve sterilisation. In tomatoes there is a variability of acidity between cultivars. Product formulation can be used to overcome this variability either by blending high and low acidity cultivars or by the addition ofshould then be confirmed by a scientific approach outlined in Section 10.4. Once the shelf-life has been determined there are a number of factors which will affect shelf-life as described below. These also need to be considered at the product development stage to ensure that they are under control during routine production of the product. 10.2.2 Raw materials The raw materials used in the preparation of a product will influence the biochemistry and microbiology of the finished product. In order to achieve a consistent shelf-life, the quality of the raw materials needs to be standardised and the attributes most likely to affect product shelf-life should be laid down in specifications. Variations in the quality of raw ingredients can lead to variations in the final product which may affect product shelf-life. Variations in raw material can occur for a number of reasons: natural variation, variety change, a change of supplier, seasonal availability or pre-processing applied to raw materials. The manufacture of coleslaw provides an example of where shelf-life can be influenced by the seasonal availability of freshly harvested cabbage which has a low yeast count, whereas cabbage from cold storage has a higher yeast count. Use of cabbage from cold stores results in coleslaw with a markedly shorter shelf-life owing to the higher starting levels of yeast introduced via the raw ingredients. If an ingredient for a raw product does not meet an agreed specification, e.g. for levels of microorganisms, it is still possible to use the ingredient for a different purpose, e.g. to be added to a product before cooking, provided there is no compromise to food safety. The likely consequences of using higher levels of organisms can be evaluated using predictive models (Section 10.3). Tolerance limits for those ingredients that exert a key preservative effect in the final product, such as the percentage of salt, need to be established during the development of the product or in challenge testing (see Section 10.6) and be stated in the product process and formulation specifications. Any variability in the levels of these ingredients due to inaccuracy in weighing ingredients during routine production will affect the shelf-life achieved. Ingredients which are crucial to product safety or stability during the assigned shelf-life should be identified using product hazard analysis (Leaper 1997) and the levels of these ingredients must be controlled during routine production. For example, for chilled MAP foods a salt level of 3.5% in the aqueous phase can be a key controlling factor for these foods and the salt level must be monitored for each batch of product manufactured (Betts 1996). Product formulation can be used to overcome natural variability of critical factors in raw materials and thereby reduce the variation of the final product. The pH is one of the most important factors affecting the degree of heat processing required to achieve sterilisation. In tomatoes there is a variability of acidity between cultivars. Product formulation can be used to overcome this variability either by blending high and low acidity cultivars or by the addition of 262 Chilled foods