Coffee chemistry from an expert

in Storing Coffee

The following great information is from long-time guest John Hayes.  Just when you think you know everything, somebody with a particular background can show you how much more there is to learn.
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I’m a chemist.  I’m a senior, graduating this spring and moving on to grad school, hopefully, and I can tell you that storing coffee in any kind of plastic container is a bad idea because plastic is porous. While it might not let water in and out to the naked eye, at the molecular level, it does allow a very slow dissipation of atmospheric oxygen in and out.



Most of the reason coffee goes “bad” is because it goes rancid, that is, the naturally-occurring unsaturated fatty acids in the coffee oxidize, which is caused by reaction with oxygen, especially in the presence of light. So, believe it or not, if you were to put some coffee in a plastic bag or container and leave it on your windowsill, it would probably taste pretty different after a week. After a while, it’s just going to taste sour and disgusting because humans are built to detect rancid things.  It’s a sign that something is too aged to eat in nature.

If you don’t clean your coffeemaker and notice that it smells like, well, smells bad, you’re smelling rancid coffee, the reason people need to use soap and water on everything coffee comes into contact with (coffeemaker parts), as you properly state on the site. Soap will remove these fatty acids.

For storage, what I did was get a glass jar from Wal-Mart, the kind that clamps the lid down onto the jar and has a rubber seal, and then I put that in a dark corner in my kitchen. This alone makes one heck of a difference. My dad used a fairly robust Tupperware container for his coffee for the longest time, and I converted him to these things and he loves them. With these glass jars, the coffee will stay brand new for at least two weeks. After a month, there is a slight loss in freshness since no seal is perfect, but it’s still very tolerable.

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Thank you, John, great contribution.

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