I found about 10 bags of various beans from a trip to Costa Rica in 2004. Bags are dated 2004. None say they are roasted. Got them tour of Cafe Britt. We stopped grinding long ago.... What are the odds
A) this is dangerous to brew B) tastes good enough to bother to grind and brew them?
Been in their original box in a dark pantry air-conditioned home
Raw green coffee has a shelf life of about one year. Roasted beans last from a few days up to a year depending on how packaged; ground coffee even less than that. (source)
Based on that, the probability of B is practically zero, so I wouldn't risk finding out about A! (Seriously though, if the beans are at all mouldy, don't use them.)
The coffee will not taste good, it's been standing around for way too long. If you tried to brew it, it would taste like cardboard, wood and maybe ash. Roasted coffee tastes best a few days and up to a few weeks after roasting, then the taste starts degrading.
There might actually be some mold and bacteria in those coffee bags if they haven't been vacuum sealed.
If it's green coffee and you have a roaster go ahead and roast them. They will probably still taste cardboard-y but with temperatures of above 200°C during roasting you won't have to worry about bacteria. If it's roasted coffee, I'd just throw it away. If you're really emotionally attached to it, you might try to brew it once and taste a little. The chances of you dying or having severe reactions to it is fairly low if you don't drink it in large quantities.
Coffee is not like whiskey or wine, it won't be better with age, quite the opposite actually, so it's not going to be good. If it's moldy or smells rotten I wouldn't try it but if you want to you can brew a little bit to see what it tastes like.
