title_body: Is it safe to brew old coffee?
upvoted_answer: If it's refrigerated, it'll last for at least a week, as long as you didn't pre-dairy it.
    Unrefrigerated, I wouldn't trust it for more than a day. Coffee is a crappy growth medium        and it should start out the next best thing to sterile, but, even covered, its going to start to get moldy.
    Obviously if you add dairy, then you're dealing with that dairy shelf-life, and that isn't very long at all.
  
  
  First, is your idea of going bad that it has a funny taste and is not as fresh as it once was, or is it that it actually tastes as though it is spoiled? Yes, coffee can go stale when it comes to taste, but it won’t actually be spoiled or dangerous to drink.
  
  Once your coffee is opened and introduced to oxygen, the shelf life timer begins to tick. Storing coffee in hot, humid, or sunlight areas will only make matters worse. The best way to keep your coffee fresh is to store it in a container that is air tight and will remain cool – but not in the refrigerator.
  
  Do you typically buy your coffee ground for you? With a far greater surface area of coffee coming in contact with the oxygen, those grounds are going to stale much quicker than whole beans will. I highly recommend investing in a hand or electric grinder to experience the fresh taste and aroma of beans you’ve ground yourself.
  
  When coffee goes bad, it can become bitter and even rancid. Every bean will react differently to oxidation. If you start to notice your expertly roasted beans losing quality and general yumminess, it may be time to buy some fresh beans. Don’t know how to find amazing, fresh coffee? I wrote a guide on that.
  
  No matter what you do, you will not be able to get that fresh flavor back once it has left the bean. The most important thing to do is keep it locked up tight. However, if you are a true coffee lover, it may not sit around long enough to even think about going bad. Just remember this rule of thumb: about two weeks after roast the coffee will start decaying.
  
  I would close this question as "Too broad" but then.
  
  Sourced from http://www.coffeebrewguides.com/ and https://cooking.stackexchange.com/