Hi Poet,
This is an excellent discussion. Understanding the true shelf life of a product goes far beyond reading the "expiration" date on the package. I studied food preservation technology some years ago, which led into an interest in the process of expiration dating products. There are some excellent books (written for industry) on the process of choosing expiration dates for various products. Whe time when a product becomes unsafe or ineffective is not necessarily the only factor that goes into the printed "expiration" date. In fact for many types of products, the expected useful life is a minor or even insignificant factor in the choice of expiration date.
Some examples:
FOOD:
Perception of freshness. The desire that food be perceived as "fresh" is a major concern of food producers. It might well be that Twinkies (given what they're made of) could remain fresh and moist well into the next decade. But nobody likes feeling as though the food they are eating could be surplus from the Korean War. So food producers generally stick to one or two year expiration dates, even where the food (like soy milk) could be good for longer.
The germination rate of seeds will vary with the seed, and is extremely dependent on moisture and oxygen concentration. Seeds which will remain viable for decades in the complete absence of moisture may spoil within several years in the presence of small amounts of water vapor.
Canned goods will never be unsafe to eat, although since they are packed in water the food product will eventually macerate.
STERILE MEDICAL SUPPIES:
Package integrity. A sterile item (like a lancet or catheter), or even sterile canned or packaged water, will never become "unsterile" just by sitting on the shelf. Louis Pasteur proved that in the 1860's. But companies worry about how long packages will hold up under continuous jostling and handling in storerooms. If your package is sitting on the shelf undisturbed, you needn't worry.
PHARMACEUTICALS:
Liability control: Every unconsumed pill is a potential legal liability. Companies don't want a large pool of their products floating around the world for years and years like little ticking time bombs. By setting short expiration dates, companies' insurance costs go down, because at any given time there will be a much smaller pool of drugs that could get the company into trouble.
Pharmaceuticals require careful individual research, because you have to know the particular chemical characterisitcs of the drug you are using. For example penicillin, ampicillin, amoxicillin (and other beta-lactam antibiotics) generally lose strength slowly while sitting on the shelf. (See also references below.) As the army found out, they won't lose much strength even 10 years past their expiration dates. Even then, it would be safe to simply double the doses to compensate for the loss of strength.
On the other hand, tetracyclene (a broad-spectrum antibiotic) degrades during storage into a compound that can cause Fanconi's syndrome, a form of kidney damage, and shouldn't be used after their expiration date. (Source: Dispensatory of the United States, 1960 Ed.)
Furthermore, for many modern patent drugs, shelf-life information is not available at all, because nobody cared to find out. The company that sells the drug has proven that it is stable for the 2 years that it wishes to stamp on the bottle, and that's all they need to know.
Here are a few excellent resources on shelf-stability of drugs:
"Stability of Essential Drugs in Tropical Climates"
"Drug Stability in Tropical Climates (spreadsheet)" See http://medicineproject.wikispaces.com/ for full references.
I want to start a thread intended to gather information on the shelf life and/or expiration dates of various items. This also includes techniques or methods of storage and shelf life extension, such as storage conditions and use of additives.
Examples of items I would like to see us gather information on, and receive information on:
IMPORTANT: Because people may decide to rely on this information in an unforeseeable future, If you want to post in this thread PLEASE make sure to cite credit sources, like scientific studies, etc. If it is your own personal experience, please give as much details as possible. Avoid hearsay anecdoes like: "my neighbor/grandmother/cousin says this" unless you actually sit down to interview your neighbor for details.
DISCLAIMER: Obviously something can still be unsafe even if the shelfe life or expiration date hasn't been reached yet - such as milk left on the counter or in an unreliable refrigerator. Tests and results obtained by one person or with one batch of products do not necessarily guarantee your own results will be the same. Abide by manufacturer's guidelines, and use caution and common sense. Check with an expert if you are not sure.
Helpful Resources
Shelf Life (Wikipedia article)
http://en.wikipedia.org/wiki/Shelf_life
Many Medicines Are Potent Years Past Expiration Dates (March 28, 2000)
"Fifteen years ago, the U.S. military decided to find out. Sitting on a $1 billion stockpile of drugs and facing the daunting process of destroying and replacing its supply every two to three years, the military began a testing program to see if it could extend the life of its inventory.
"The testing, conducted by the U.S. Food and Drug Administration, ultimately covered more than 100 drugs, prescription and over-the-counter. The results, never before reported, show that about 90% of them were safe and effective far past their far past their original expiration date, at least one for 15 years past it...
"One medicine the FDA has endorsed for extensions is ciprofloxacin hydrochloride tablets, an antibiotic marketed by Bayer as Cipro. One batch had an expiration date of March 1989. More than 9 1/2 years later, the FDA found the tablets still good; it then extended some of them for 18 more months and others for 24 more months."
Original Source: http://online.wsj.com/article/SB954201508530067326.html
Copy Source: http://articles.mercola.com/sites/articles/archive/2000/04/02/drug-expiration-part-one.aspx
Poet