What is food expiry date?

[lalithaniharika]

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.

[JackBean]

there is difference between expiry date and best before. Best before should be for food, which may quickly go bad, such as meat, dairy products etc. Expiry is for food, which should last for like 2 years or so.

[lalithaniharika]

I am asking about exact theory behind calculation of expiry date.On what factors do they give expiry date?How accurate is it?

[JackBean]

I'm sorry, I cannot help you with that since I'm not into food chemistry.

[ChesneMD]

It, as once explained to me by in simplest terms by a professor, is the date at which it would take bacteria, fungi, etc to defile the product, which leads to expiration. For instance, canned food lasts longer because of the intense nature of the method - anaerobic bacteria, however, can negate this, as previously seen in Botulism.

But the science behind it is very accurate, up to the point of which we know what we're dealing with; we are still learning. But that should be enough for your answer, I hope. It is based on the microbes, etc. And of course, I should mention, the accuracy is also determined on average usage, or in some cases no usage and simply how long it takes bacteria to make home regardless (bearing in mind I am vastly simplifying the exact process).

*Edit - I replied to this, unknowingly, late, but as a result of a previous post briefly recent, which seems to have been deleted after I posted. I apologize.

[michimichi]

expiry dates can be determined through stability testing.
the sample will be incubated at different temperatures(low temp, room temp, high temp)at a certain time duration.samples will be tested monthly (for example) to test its quality if it still meets the standards (like the sensory evaluation as well as the pH, moisture,microbes).most of the time the duration for the test is also 2 yrs or depends.There is a formula for the calculation for the expiry dates but of course that will be based on the results you will gather from the stability test /study but unfortunately i dont have the formula.
Sometimes the expiry dates exceeds to the expected date of expiry.
Bur of course it also depends on what kind of food is it and how was the preparation.
Dried food or desiccated foods are obviously last longer.