May 27, 2015

Coffee Storage – Cool, Dark, Dry

Still one of the most common questions asked in this industry

“Should I store my coffee beans in the fridge?”

The answers received vary from “of course” to, “never ever” and everyone seems to have some justification as to why their own answer is correct. Often the reason is a tad illogical, like, “great aunt dotty said I should” or, “I’ve always done it this way” but mostly people just don’t stop to think about why they choose the storage method they use.

The 20% of oxygen in the air around us is the enemy of a coffee bean. Oxygen will stale a coffee bean faster than just about any other poor storage method. Keeping your coffee in a half empty tin will trap a lot of air in the container, and the oxygen will continue to oxidise the coffee. This is made worse each time you remove the lid, as the volume of air is replaced with more oxygen and the cycle continues.
Water not only brings out the aroma of coffee by valorising the volatile oils; it also does a great job of staling coffee beans. Keep them dry until you need to use them to get the very best out of the bean.
Direct sunlight is bad, but even indirect sunlight can help speed the staling process. Most commercial coffee hoppers are tinted to get a compromise between keeping the light out and still being able to see how much coffee is in there.
Good packaging that acts as a barrier to light and oxygen will keep coffee at its best until it’s opened.  Obviously the inside of the packaging also needs to be food safe too. Mostly the industry uses three layer foil bags to protect coffee; the outside layer and inside layers are mostly low density polyethylene (LDPE) or polypropylene (PP) with the foil in the middle acting as an air barrier. We use bio degradable cornstarch with foil in the middle, but it acts the same. A small amount of air will be trapped in the bag when packing but if well sealed, the oxygen is “consumed” by the beans and staling stops after a few days. Some roasters use nitrogen flushing to help remove more of the air. For the most part it makes little difference and might only really become a benefit for long term storage. I would rather purchase fresh coffee more often than to store it.
Coffee people often refer to the wine industry for guidance; the wine guys have been tweaking the beverage science a lot longer than most of the coffee industry, and quite often their ideas work well with coffee too.
There is a product in the wine industry called Wine Save. It’s simply a can of argon gas that you squirt into an open bottle of wine, keep it upright and cap it again to stop oxidisation.   Argon gas is inert, tasteless, odourless and heavier than air, so squirting some into a wine bottle will leave a layer sitting on top and provide a barrier between the wine and oxygen. At $0.35 an application, it might work on a bag of coffee beans or in the hopper of your grinder too; let me know if you try it!
Keeping coffee in a normal fridge will cool it too much and when opened in a warm room, it will suck all the humidity from the air and absorb the condensation that forms on the cold beans. Coffee is hygroscopic and will attract and hold water at a fast rate. Keep your milk in a 4 degree fridge, not your coffee. There is a more recent move to keeping coffee in wine refrigerators, which has some merit if you set them on the higher scale. Wine is often stored in the 12°C – 20°C range; if you stored coffee at 20°C, the differential between the fridge and the ambient temperature in the room would be low and condensation would be minimal. This could help in very hot and humid climates. but obviously has some running costs and storage space considerations too.
A late night whacky thought of mine with zero scientific research to back it up went something like this … A fresh roasted coffee bean gives off carbon dioxide; carbon dioxide is heavier than air. If you filled a hopper with a kilo of beans and left the lid on it, the oxygen in the hopper would mostly convert to carbon dioxide and because CO2 is heavier than air, the slight positive pressure of the beans degassing would provide a similar inert gas barrier to Argon and Nitrogen flushing. This has the potential of being better than tipping the hopper full of beans back into the bag at night, as less disturbance would mean less oxygen contact. The few trials I did of this method seemed to work well on nearly full hoppers of recently roasted coffee. So undisturbed beans might keep OK in the hopper, which really goes against what I expected when I first tested it.
My own personal answer to coffee bean storage is “cool, dark, dry, somewhere like your pantry” and for the most part that’s enough to keep most coffee beans happy for short periods of time. I think the real punch line is, order fresh coffee more often, store as little as possible, worry much less and enjoy far more.
About the Author
Andy Freeman owns and runs
Fresh roasted coffee, green beans and Australia’s biggest coffee forum

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