[Jimbee (OP)]

Can coffee or tea ever really go bad? I mean in dry form or as the beverages? Because, in HS I once used a container of 10-year-old teabags. And the cup of tea they made tasted just fine. I know if I keep a prepared pot of coffee or tea laying around couple of days, there never seems to be a problem with it. Unless I add cream. Cream of course can always go bad, and usually in a day of course, if left out.

I know I learned, also around HS, liquid medicines like Pepto Bismol never go bad. They lose their potency, but they never go bad. Because they have nothing in them that food poisoning microorganisms would be interested in. Tea and coffee are foods, of course. But they work differently, I've noticed. I know they have 40 year old Scotches and hundred year old wines. But those two go bad too. Just after, oh I don't know, maybe 500 years, maybe a thousand.

[chris]

Different foodstuffs rot at different rates.

Dried materials - like tea and coffee - will deteriorate more slowly, but they will still perish. Volatiles in the material will slowly be lost; also, ongoing chemical reactions between the entities they contain will change the flavour and palatability over time.

Wine, for example, continues to evolve in the bottle. The thousands of molecules in the liquid react to produce new species. This alters the character of the beverage over time. This is why some wines have a short "bottle age" while others "age well".

Medicines are similar. Some are very stable molecules that will last forever. Others are more fragile, and or mixtures that may react or decay, potentially affecting potency.

[Petrochemicals]

Go bad is a bit ambiguous, i thinnk the tea bags in the compost would be considered as bad. Tea looses its pernache, as does coffee which is why people who are cofficianadoes are well known for grinding their own beans.

Depending on the conditions im sure coffee and tea could be infested with fungus, parasites etc if not stored correctly. Similarly flour can be infected with mites or go stale.

[paul cotter]

In the absence of microbiologic contamination rancidity is a problem in long term storage. This happens when oxygen adds to double bonds in unsaturated fatty acids. Vacuum packing should address this problem.

[diverjohn]

Coffee suppliers suggest keeping roasted coffee beans in dark cool storage as oxygen and sunlight will cause degradation.
As for fungus, I believe coffee was roasted either to kill the fungus or at least hide the taste of mold, or it was roasted before shipping so the mold wouldn?t find nutrients and moisture.