What is food expiry date?

[niharika]

I need to do some innovative project in my college.I am planning to compare microbial content of foods with different expiry dates.In order to write principle for that experiment, I need to understand what exactly is the expiry date.Most of the foods will be fine even after expiry date.Why??What is the basis for calculating expiry date?Is there any difference between expiry date and other forms of it like best before..etc..If there are any aspects of this experiment, please do mention them.Thanks in advance.

[michel123456]

I am afraid you are going into trouble.

As far as I know, expiry date is a matter of marketing, of industrial interests & even of politics, not only a matter of science.

 

For example the expiry date of fresh dairy products in my country is 4 days, not because fresh milk gets bad in 4 days in the refrigerator, it can stand 10 days or more, but because with an expiry date of 10 days the local market would be infested with low cost fresh milk coming by trucks from Germany, Holland, Belgium or Austria. This would destroy the flourishing local dairy companies that sell milk over price.

[insane_alien]

expiry date is almost never a calculated value.

 

what typically happens is they take a sample of the product (preferably from several batches) and to stability testing. They'll store the product in a variety of conditions and test the quality at set intervals. They'll take the average and put in a safety factor (15% is bandied about a lot) and then whap it on the packaging.

 

so for milk, they'll take maybe 100 bottles, store twenty each in different conditions and then take one bottle from each location every day and test it for 20 days.

 

but then then a michel says, sometimes it's government mandated regardless of reality and sometimes companies will just guess.

 

I wouldn't really call expiry dates calculated, more vague rule of thumb guideline that applies in certain circumstances.

 

I can take any product and make it expire long before the expiry date says it should and i can keep it fresh long after the expiry date says it should have turned to mush.

 

If you can come up with a way to accurately predict expiry dates then many many companies will be willing to pay you lots and lots of money.

[niharika]

ohh!!!Is it so??its too bad :unsure:there should be some reason for which the product stays fresh before expiry date!!

 

If this is true, all different foods manufactured in different conditions should have different expiry dates.Will it be like that?

[insane_alien]

well of course there are reasons that food expires. bacterial growth, degradation of chemicals within the food etc. The whole problem is that there are so many variables that affect the shelf life that it is almost impossible to predict. In order to get a truly accurate picture you'd have to spend millions on stability trials. and even then, it would be impossible to reduce the data you get from those trials down to something so simple as 'this product will expire in x days'

 

and yes, different foods manufactured in different conditions will have different expiry dates. and even the same foods manufactured in the same conditions can and will have different (exact) expiry dates.

 

and then there is storage. the temperature and humidity can have a massive impact upon how soon a food will become rancid.

 

for a college project you'll probably want to reduce this to one or two variables and a few types of food(as you are probably limited in time you should pick something with a short shelf life).

 

when a food will expire is the million dollar question among food manufacturers.

[michel123456]

Expiry date is not the date when a product becomes bad for consumption. On some products it is mentioned "best before ...", which means "if you want to get full [proteins,vitamins,etc.] of this product, consume it before..."

 

It is important for medecines. In most case, if you take some medecine (a pill of some sort) after the expiry date, that does not mean you will become sick, but that the dose of the active product will be reduced.

[insane_alien]

Expiry date is not the date when a product becomes bad for consumption. On some products it is mentioned "best before ...", which means "if you want to get full [proteins,vitamins,etc.] of this product, consume it before..."

 

It is important for medecines. In most case, if you take some medecine (a pill of some sort) after the expiry date, that does not mean you will become sick, but that the dose of the active product will be reduced.

 

Ah, yeah, probably wasn't clear in my posts that I was using expiry as date after which it is 'not fresh'. sorry.

 

medicines are easier than foods as it is typically one or two chemicals(active ingredient and an inert filler usually) in a very well sealed package and with plenty of quality control at the manufacturing end. It removes a great deal of the variables found in foods which are more complex and have less rigorous standards.

[niharika]

Thanks for giving many details

I would like to ask one more thing.What should be the title of experiment??

I already thought of two titles, but our sir rejected them.He is very particular about terms and their meanings in title.one is "study of types of micro organisms in expired food and fresh food".My sir told me that it is not possible to study all types of bacteria as it is very short term project.So he asked me to change "study of types", then again I went with another title."differentiation of microbial content of expired food and fresh food". Sir again said that their wont be anything called as expired or fresh food.He asked me to use term "expiry date". So can anyone suggest me some title?

 

If possible please provide me with articles related to expiry dates or give me some website names or books and authors names.

[StringJunky]

It's also called 'shelf life':

 

http://en.wikipedia.org/wiki/Shelf_life

 

Here's a source of a few links you might find useful

 

http://ec.europa.eu/food/food/biosafety/salmonella/microbio_en.htm

[niharika]

Thank you soooo much!!source is wonderful.

[visionsen]

We learn everyday l thought expiry dates and best before are the same but now l know better.

[granpa]

http://consumerist.com/2008/12/cheat-sheet-for-sketchy-food-expiration-codes.html