title_body: How does moisture occur inside Trader Joe’s coffee cans?
upvoted_answer: Are you sure it is water? If you bought a dark roast, there is a distinct possibility that there is a bit of oil in the coffee. 
  Another possibility is a minor machine malfunction during the roasting process. With large scale coffee roasters, a small amount of water is sprayed directly into the drum just before dumping to "quench" the coffee and speed the cooling process. Almost all of this water evaporates immediately under normal circumstances. As a technician in the coffee industry, I have seen a couple issues that caused more water to go into the beans than intended, and the whole batch had to be thrown out. 
  Hopefully it ends up being oil. In either case, as long as the coffee isn't moldy or foul smelling, it should be just fine.