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Why Does Coffee Go Stale?

bad tasting coffee

I just opened a brand new bag of decaf that I've had hanging around for about a month.  Of course, it tasted like coffee that was roasted a month ago.  No surprise there.  I buy decaf in case I want to brew a pot after work and don't want to be up all night.  The problem is that I don't do that often enough to go through a bag before it gets stale.  This started me wondering what exactly it is that causes coffee to go stale, and if there's anything that can prevent it or at least slow it down.  


After some casual reading and sipping stale decaf, the consensus seems to be that Oxygen is to blame.  

"Just as iron is oxidized to form rust, stale coffee is what you get when roasted beans (or grounds) have been oxidized from exposure to oxygen; the more intense the exposure, the more quickly oxidized and stale your coffee will become. Other factors such as heat and moisture can also make oxidation occur. In your mug: rancid, bitter coffee for which no brewing technique on earth can undo the damage."   -

The Test

So if I can keep my roasted whole beans oxygen free, they'll last longer?  Sounds like a simple enough theory to test.  I ordered some oxygen absorbers and 4oz glass glass jars from Amazon.  The plan is pretty simple.  I'll split a 12oz bag of beans into 4 jars, and put an oxygen absorber in 3 of them.  Then, over the course of a month...

  • Week 1:  Let the beans age for a week before beginning.
  • Week 2:  Open jar 1 and compare against control jar.
  • Week 3:  Open jar 2 and compare against control jar and jar 1.
  • Week 4: Open jar 3 and compare against control jar and jars 1 and 2.

Each week I'll do a blind tasting and compare the new jar against the control and the previous jars.  If I can correctly rank them by age, then I can conclude that keeping the beans oxygen free will in fact keep them fresher longer.  And if THAT's the case, I might end up just repackaging all my beans like this from now on.  It was only $12 for a pack of 50 oxygen absorbers, which only ends up being about $1 per bag of coffee.  Pretty cheap if the last scoop of a bag could taste as fresh as the first scoop.  Expecially for decaf, which I like to have available but don't use that often.

I'll post updates over the next few weeks with the results!

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