ok, genuinely interesting, but from a guy that makes food for a living do you believe we should adhere to the dates on food packaging? Chilled foods I would probably consider high risk, should I eat my sealed unopened potato salad that is 5 days past it's use by date or bin it?
I believe you can eat foods after the dates on the packaging, but common sense should be applied. microbiological risks cannot always be seen immediately, and food can be 'off' before a visible change in it. We make and sell frozen and chilled foods. The frozen foods have 18 months shelf life and will remain safe to eat for potentially years after, though the quality may deteriorate, and this depends as much on the quality of the freezer as the foods. Chilled foods we make have 8 to 10 nights life, and microbiologically will typically become unsafe after 11 or 12 nights. sometimes this will be visible as moulds, or notifiable as a smell. On some drier chilled foods however they will be unsafe to eat, but exhibit no signs after 20 to 30 days. increased water content generally promotes visible signs, while drier food often maintain apprarance for longer. this is only a rough guide though.
PH, available water, salt and sugar contents greatly effect the safety and preservation of foods. water content of less than 14%, PH of less than 4.2/3.8 and high sugar / salt contents will prevent microbiological growth and preserve foods. hence well packaged crisps, nuts, jams, pickles and sauces (as examples) can often be shelf stable for years.
Salads, inc. potato salad etc. generally have shorter shelf lives as they are usually not heat processed prior to leaving the factory - they are classed as ready to eat and will have micro contents of 10^3 or 10^4. Heat processed foods will leave the factory with a lower micro content, typically 10^2. Inevitably lower micro contents generally mean foods will last longer. Additionally as mentioned, salads are classed as ready to eat. you eat them without further heat processing in the home and are relying on the micro state from the factopry to be low. Other foods, such as ready meals, pasties etc, which will generally start with a lower micro content are classed as ready to cook - you heat them as per validated instructions in the home which further heat processes the food and makes it safe to eat - provided micro toxins have not built up through previous micro growth, such as botulism. Hence ready meals etc. often have longer shelf lives than salads, inc. your potato salad. I would not eat a potato salad which is 5 days out of date.
Botulism killed by heat processing, but leaves toxins which will make you very ill, by contrast e coli is killed, but leaves no toxins. hence e coli (and Listeria) is (usually) an issue in ready to eat salads, meats, etc. not foods cooked properly in the customers home.
long answer - Apologies.. hope it makes sense.