Over the past 20 years or so, the chilled foods industry has been using two target pasteurisation processes for products such as chilled soups, sauces, ready meals and cooked meats to assure safety. These processes separate chilled foods into two generic categories: short shelf life products and long shelf life products (>10 days). Short shelf life products are pasteurised at 70°C for 2 minutes, whilst long life products are treated at 90°C for 10 minutes. These processes ensure product safety and aim to achieve a 6 log reduction in the food pathogen likely to be of most concern to these products, namely Listeria monocytogenes and Clostridium botulinum. As an option to achieving these target pasteurisation treatments, chilled foods can be formulated to recommended parameters in terms of pH and aw to prevent growth of these pathogens should they be present. This document looks at these two sets of controls and provides a decision tree to help manufacturers decide which controls apply to their food products.

In addition, it is recognised that there are other microorganisms which may be capable of surviving the target pasteurisation temperatures and growing in the food products during chilled storage, for example, psychrotrophic strains of Bacillus and Clostridium. This white paper describes the survival and growth characteristics of relevant bacterial species in order to understand their potential effect on product quality and shelf life of chilled pasteurised food products. In addition recent data obtained on a Campden BRI member-funded project is presented see www.campdenbri.co.uk/research/shelf-life-chilled-foods.php

Shelf-life categories

Over the past 30 years there has been continued attention given to the safety of chilled food products. There are various guidelines available to ensure the safe manufacture of chilled foods and these typically consider the microbiological risks based on the duration of their shelf life. There are 2 main categories to consider with respect to shelf life: short shelf life, i.e. <10 days and long shelf life, i.e. >10 days.

(i) Short shelf life foods <10 days

The minimum heat process currently recommended to assure safety from Listeria monocytogenes (Lm) in pasteurised chilled foods with a shelf life of more than 5 days is 70°C for 2 minutes (or a time/temperature that give equivalent lethality). Where this is not achieved then the Food Business Operator (FBO) has to demonstrate the potential or not for Lm to grow in the food during its shelf life. If a food meets one of these criteria then it is not necessary to assess the growth potential of Lm as it is considered unlikely to be able to grow.